- Volume 149, Issue 8, 2003
Volume 149, Issue 8, 2003
- Review
-
-
-
Growth in sulfidic mineral environments: metal resistance mechanisms in acidophilic micro-organisms
More LessAcidophilic micro-organisms inhabit some of the most metal-rich environments known, including both natural and man-made ecosystems, and as such are ideal model systems for study of microbial metal resistance. Although metal resistance systems have been studied in neutrophilic micro-organisms, it is only in recent years that attention has been placed on metal resistance in acidophiles. The five metal resistance mechanisms identified in neutrophiles are also present in acidophiles, in some cases utilizing homologous proteins, but in many cases the degree of resistance is greater in acidophiles. This review summarizes the knowledge of acidophile metal resistance and presents preliminary in silico studies on a few known metal resistance systems in the sequenced acidophile genomes.
-
-
- Microbiology Comment
-
- Cell And Developmental Biology
-
-
-
Control of growth, secondary metabolism and sporulation in Streptomyces venezuelae ISP5230 by jadW 1, a member of the afsA family of γ-butyrolactone regulatory genes
More LessThree new genes (jadW 1, jadW 2 and jadW 3) were isolated from a region of the Streptomyces venezuelae ISP5230 chromosome at the left-hand end of the jad cluster for jadomycin B (JdB) biosynthesis. The deduced amino acid sequence of jadW 1 showed strong similarity to gene products associated in several streptomycetes with γ-butyrolactone autoregulators controlling morphological differentiation and secondary metabolism. Examination of JadW1 for conserved domains detected a repeat sequence characteristic of proteins in the AfsA regulatory family. Insertional inactivation of jadW 1 reduced the growth rate of S. venezuelae cultures in aerated liquid media containing complex nitrogen sources and altered growth morphology in minimal medium. It also affected sporulation on agar media. Cultures of jadW 1-disrupted mutants grown under conditions supporting biosynthesis of JdB or chloramphenicol by the wild-type strain failed to produce either of the antibiotics. Complementing the disrupted strain by transformation with pJV435, containing a cloned copy of the gene, improved sporulation and restored antibiotic biosynthesis in transformants to titres close to those of the wild-type similarly transformed with pJV435 as a control. The results are consistent with a role for jadW 1 in regulating morphological and metabolic differentiation. Further sequence analysis of jadR 2, which functions with jadR 1 in stress-induced activation of JdB biosynthesis, indicated that this gene encodes a γ-butyrolactone receptor homologue. The growth-rate-sensitive phenotype of the jadW 1-disrupted mutant, and the proximity of jadW 1 to jadR 2 indicate that this region of the jad gene cluster contains a regulatory mechanism incorporating γ-butyrolactone signalling and sensitivity to environmental stress.
-
-
-
-
DNA ligase IV from a basidiomycete, Coprinus cinereus, and its expression during meiosis
DNA ligase IV is thought to be involved in DNA double-strand break repair and DNA non-homologous end-joining pathways, but these mechanisms are still unclear. To investigate the roles of DNA ligase IV from a biologically functional viewpoint, the authors studied its relationship to meiosis in a basidiomycete, Coprinus cinereus, which shows a highly synchronous meiotic cell cycle. The C. cinereus cDNA homologue of DNA ligase IV (CcLIG4) was successfully cloned. The 3·2 kb clone including the ORF encoded a predicted product of 1025 amino acid residues with a molecular mass of 117 kDa. A specific inserted sequence composed of 95 amino acids rich in aspartic acid and glutamic acid could be detected between tandem BRCT domains. The inserted sequence had no sequence identity with other eukaryotic counterparts of DNA ligase IV or with another aspartic acid and glutamic acid rich sequence inserted in C. cinereus proliferating cell nuclear antigen (CcPCNA), although the length and the percentages of aspartic and glutamic acids were similar. In addition, the recombinant CcLIG4 protein not only showed ATP-dependent ligase activity, but also used (dT)16/poly(dA) and (dT)16/poly(rA) as substrates, and had double-strand ligation activity, like human DNA ligase IV. Northern hybridization analysis and in situ hybridization indicated that CcLIG4 was expressed not only at the pre-meiotic S phase but also at meiotic prophase I. Intense signals were observed in leptotene and zygotene. Based on these observations, the possible role(s) of C. cinereus DNA ligase IV during meiosis are discussed.
-
- Biochemistry And Molecular Biology
-
-
-
Bacterial ceramides and sphingophospholipids induce apoptosis of human leukaemic cells
The genus Sphingobacterium, whose members are Gram-negative non-fermentative rods, possesses ceramides and related sphingophospholipids (SPLs) with isoheptadecasphinganine and 2-hydroxy or non-hydroxy isopentadecanoic acid. This paper reports evidence that ceramides isolated from Sphingobacterium spiritivorum ATCC 33861 induce endonucleolytic DNA cleavage in human myeloid leukaemia HL-60 cells in vitro, which is the primary characteristic biochemical marker for apoptosis or programmed cell death. Ceramides and SPLs also induced DNA fragmentation and caspase-3 activation, followed by changes in morphology, such as alterations in the size of nuclei and cells, and cell cycle shortening. Apoptotic activity correlated with the ceramide structure. Ceramide with a 2-hydroxy fatty acid showed stronger apoptotic activity than ceramide with a non-hydroxy fatty acid. Furthermore, the major five SPLs (ceramide phosphorylethanolamine-1 and -2, ceramide phosphorylinositol-1 and -2, and ceramide phosphorylmannose-1) showed apoptosis-inducing activity in HL-60 cells, indicating that the ceramide moiety of the SPLs plays a crucial role as the intracellular second messenger but that their hydrophilicity is less important in this regard. The hydrophilic part of SPLs may play a role in other cellular response systems. The involvement of Fas antigen was implicated in the apoptotic event since Fas antigen expression was observed after 3 or 4 h stimulation of HL-60 cells with bacterial ceramides. However, a time-course study for caspase-3 activation indicated maximal activity at 1 h after stimulation with bacterial ceramides, suggesting that two (or possibly more) mechanisms of signal transduction, Fas-dependent and Fas-independent, may be involved. Fas antigen expression and caspase-3 activation by five kinds of SPLs were observed after 3 or 4 h. These results indicate that there is a difference in the response of HL-60 cells to bacterial ceramides and SPLs.
-
-
-
-
Metal-responsive elements in Pleurotus ostreatus laccase gene promoters
More LessFungal laccase gene transcription is strongly induced by copper ions; notably, some laccase promoters contain multiple putative metal-responsive elements (MREs). Previously, it has been demonstrated that the Pleurotus ostreatus laccase genes poxc and poxa1b are transcriptionally induced by copper, and several putative MREs were found in the promoter regions of these genes, which extend for about 400 nt upstream of the start codon (ATG). Identification of MRE sequences, which are protected by protein binding in the poxc and poxa1b promoter regions, has been achieved by footprinting analyses. Electromobility shift assays led to the evaluation of the ability of the identified MREs to bind protein(s), and the role of specific nucleotides of these elements in complex formation has also been analysed. The formation of complexes between analysed MREs and fungal proteins requires the absence of metal ions. Proteins extracted from fungus grown in copper-depleted medium are able to form complexes with MREs, whilst proteins extracted from fungus grown in copper-containing medium are able to form complexes only in the presence of a metal chelator. Moreover, copper-depleted proteins are unable to form complexes when copper or zinc ions are added. UV-cross-linking analyses led to the determination of the molecular masses of the MRE-binding proteins. In the poxa1b promoter, a GC-rich region, homologous to the core binding site for transcription factor Sp1, decreases the binding affinity of the adjacent MRE, affecting its interactions with fungal protein factors.
-
-
-
Carbon-source-dependent nitrogen regulation in Escherichia coli is mediated through glutamine-dependent GlnB signalling
More LessThe PII signal transduction proteins GlnB and GlnK are uridylylated/deuridylylated in response to the intracellular glutamine level, the primary signal of the cellular nitrogen status. Furthermore, GlnB was shown to be allosterically regulated by 2-oxoglutarate, and thus GlnB was suggested to integrate signals of the cellular carbon and nitrogen status. Receptors of GlnB signal transduction in Escherichia coli are the NtrB/NtrC two-component system and GlnE, an enzyme which adenylylates/deadenylylates glutamine synthetase. In this study, the authors investigated the effect of different carbon sources on the expression of the NtrC-dependent genes glnA and glnK and on the uridylylation status of GlnB and GlnK. With glutamine as nitrogen source, high levels of glnA and glnK expression were obtained when glucose was used as carbon source, but expression was strongly decreased when the cells were grown with poor carbon sources or when cAMP was present. This response correlated with the uridylylation status of GlnB, suggesting that the carbon/cAMP effect was mediated through GlnB uridylylation, a conclusion that was confirmed by mutants of the PII signalling pathway. When glutamine was replaced by low concentrations of ammonium as nitrogen source, neither glnAglnK expression nor GlnB uridylylation responded to the carbon source or to cAMP. Furthermore, glutamine synthetase could be rapidly adenylylated in vivo by the external addition of glutamine; however, this occurred only when cells were grown in the presence of cAMP, not in its absence. Together, these results suggest that poor carbon sources, through cAMP signalling, favour glutamine uptake. The cellular glutamine signal is then transduced by uridylyltransferase and GlnB to modulate NtrC-dependent gene expression.
-
-
-
Overexpression of the polynucleotide phosphorylase gene (pnp) of Streptomyces antibioticus affects mRNA stability and poly(A) tail length but not ppGpp levels
More LessThe pnp gene, encoding the enzyme polynucleotide phosphorylase (PNPase), was overexpressed in the actinomycin producer Streptomyces antibioticus. Integration of pIJ8600, bearing the thiostrepton-inducible tipA promoter, and its derivatives containing pnp into the S. antibioticus chromosome dramatically increased the growth rate of the resulting strains as compared with the parent strain. Thiostrepton induction of a strain containing pJSE340, bearing pnp with a 5′-flanking region containing an endogenous promoter, led to a 2·5–3 fold increase in PNPase activity levels, compared with controls. Induction of a strain containing pJSE343, with only the pnp ORF and some 3′-flanking sequence, led to lower levels of PNPase activity and a different pattern of pnp expression compared with pJSE340. Induction of pnp from pJSE340 resulted in a decrease in the chemical half-life of bulk mRNA and a decrease in poly(A) tail length as compared to RNAs from controls. Actinomycin production decreased in strains overexpressing pnp as compared with controls but it was not possible to attribute this decrease specifically to the increase in PNPase levels. Overexpression of pnp had no effect on ppGpp levels in the relevant strains. It was observed that the 3′-tails associated with RNAs from S. antibioticus are heteropolymeric. The authors argue that those tails are synthesized by PNPase rather than by a poly(A) polymerase similar to that found in Escherichia coli and that PNPase may be the sole RNA 3′-polynucleotide polymerase in streptomycetes.
-
-
-
CloN2, a novel acyltransferase involved in the attachment of the pyrrole-2-carboxyl moiety to the deoxysugar of clorobiocin
More LessThe aminocoumarin antibiotic clorobiocin contains a 5-methylpyrrole-2-carboxylic acid unit, attached via an ester bond to the 3-OH group of the deoxysugar moiety. To investigate candidate genes responsible for the formation of this ester bond, a gene inactivation experiment was carried out in the clorobiocin producer Streptomyces roseochromogenes var. oscitans DS 12.976. An in-frame deletion was created in the coding sequence of the gene cloN2. The production of secondary metabolites in the wild-type and in the cloN2 mutant was analysed. The wild-type showed clorobiocin as the main product, whereas the cloN2 mutant accumulated a new aminocoumarin derivative, novclobiocin 104, lacking the pyrrole moiety at the 3-OH of the deoxysugar. In addition, free pyrrole-2-carboxylic acid accumulated in the culture extract of the cloN2 mutant. The structures of the metabolites were confirmed by NMR and LC-MS analysis. Clorobiocin production was successfully restored in the cloN2 mutant by introducing a replicative plasmid containing the cloN2 sequence. These results prove an involvement of cloN2 in the formation of the ester bond between the pyrrole moiety and the deoxysugar in clorobiocin biosynthesis. Furthermore, they indicate that the C-methylation at position 5 of the pyrrole moiety occurs after the attachment of pyrrole-2-carboxylic acid unit to the deoxysugar moiety.
-
-
-
Optimization of signal peptide SP310 for heterologous protein production in Lactococcus lactis
More LessThe authors have previously reported the identification of novel signal peptides (SPs) from Lactococcus lactis using transposon insertion. Of these, SP310 caused the highest level of secretion. However, the levels were lower than those obtained using the signal peptide from Usp45 (SPUSP), the major secreted lactococcal protein. In this study, site-directed mutagenesis of signal peptide SP310 was used to investigate the effect of amino acid alterations on lactococcal secretion and to improve secretion efficiency. Several mutated SPs caused higher secretion. This increase in secretion was due to modifications in the cleavage region. In fermenter experiments, the signal peptide SP310mut2 resulted in an extracellular Staphylococcus aureus nuclease (Nuc) yield which was 45 % higher than that with the natural SP310. Surprisingly, increasing the hydrophobicity of the hydrophobic core or increasing the number of positively charged amino acids in the N-terminal region of SP310 decreased secretion. High extracellular yields of Nuc resulted from more efficient secretion, as strains with less efficient SPs accumulated more intracellular SP-Nuc precursor.
-
-
-
Role of GlnB and GlnK in ammonium control of both nitrogenase systems in the phototrophic bacterium Rhodobacter capsulatus
In most bacteria, nitrogen metabolism is tightly regulated and PII proteins play a pivotal role in the regulatory processes. Rhodobacter capsulatus possesses two genes (glnB and glnK) encoding PII-like proteins. The glnB gene forms part of a glnB–glnA operon and the glnK gene is located immediately upstream of amtB, encoding a (methyl-) ammonium transporter. Expression of glnK is activated by NtrC under nitrogen-limiting conditions. The synthesis and activity of the molybdenum and iron nitrogenases of R. capsulatus are regulated by ammonium on at least three levels, including the transcriptional activation of nifA1, nifA2 and anfA by NtrC, the regulation of NifA and AnfA activity by two different NtrC-independent mechanisms, and the post-translational control of the activity of both nitrogenases by reversible ADP-ribosylation of NifH and AnfH as well as by ADP-ribosylation independent switch-off. Mutational analysis revealed that both PII-like proteins are involved in the ammonium regulation of the two nitrogenase systems. A mutation in glnB results in the constitutive expression of nifA and anfA. In addition, the post-translational ammonium inhibition of NifA activity is completely abolished in a glnB–glnK double mutant. However, AnfA activity was still suppressed by ammonium in the glnB–glnK double mutant. Furthermore, the PII-like proteins are involved in ammonium control of nitrogenase activity via ADP-ribosylation and the switch-off response. Remarkably, in the glnB–glnK double mutant, all three levels of the ammonium regulation of the molybdenum (but not of the alternative) nitrogenase are completely circumvented, resulting in the synthesis of active molybdenum nitrogenase even in the presence of high concentrations of ammonium.
-
-
-
A specific role of the Saccharopolyspora erythraea thioesterase II gene in the function of modular polyketide synthases
Bacterial modular polyketide synthase (PKS) genes are commonly associated with another gene that encodes a thioesterase II (TEII) believed to remove aberrantly loaded substrates from the PKS. Co-expression of the Saccharopolyspora erythraea ery-ORF5 TEII and eryA genes encoding 6-deoxyerythronolide B synthase (DEBS) in Streptomyces hosts eliminated or significantly lowered production of 8,8′-deoxyoleandolide [15-nor-6-deoxyerythronolide B (15-nor-6dEB)], which arises from an acetate instead of a propionate starter unit. Disruption of the TEII gene in an industrial Sac. erythraea strain caused a notable amount of 15-norerythromycins to be produced by utilization of an acetate instead of a propionate starter unit and also resulted in moderately lowered production of erythromycin compared with the amount produced by the parental strain. A similar behaviour of the TEII gene was observed in Escherichia coli strains that produce 6dEB and 15-methyl-6dEB. Direct biochemical analysis showed that the ery-ORF5 TEII enzyme favours hydrolysis of acetyl groups bound to the loading acyl carrier protein domain (ACPL) of DEBS. These results point to a clear role of the TEII enzyme, i.e. removal of a specific type of acyl group from the ACPL domain of the DEBS1 loading module.
-
-
-
Cloning and functional expression of dipeptidyl peptidase IV from the ruminal bacterium Prevotella albensis M384T
More LessRuminal bacteria of the genus Prevotella play a crucial role in peptide breakdown in the rumen, a component of protein catabolism that leads to the inefficient use of dietary protein by ruminant animals. This is the first report of the cloning of a peptidase gene from a ruminal bacterium. Part of the dipeptidyl peptidase type IV (DPP-IV) gene from Prevotella albensis M384T was cloned using degenerate primers designed from conserved regions found within other known DPP-IV sequences. Flanking regions were determined by genomic walking. The DPP-IV gene was expressed in Escherichia coli. The cloned enzyme required a free N terminus and catalysed the removal of X-Pro dipeptide from proline-containing oligopeptides, where proline was the second residue from the N terminus. It was inhibited by serine protease inhibitors and the substrate analogue for mammalian DPP-IV, diprotin A. The properties of the cloned enzyme were similar to those of the native form in P. albensis and, in general, DPP-IVs from other organisms. The enzyme contained a conserved motif which is associated with the S9 class of prolyl oligopeptidases. The DPP-IV gene appeared not to be part of a contiguous operon. Regions with similarity to other putative promoters of Prevotella spp. were also identified. Construction of a phylogenetic tree demonstrated that the DPP-IV of P. albensis clusters with other DPP-IVs found in bacteria of the Cytophaga–Flexibacter–Bacteroidaceae (CFB) phylum, which are more closely related to eukaryotic DPP-IVs than the DPP-IV-like enzyme (PepX) of the lactic acid bacteria.
-
-
-
Dynamic FtsZ polymerization is sensitive to the GTP to GDP ratio and can be maintained at steady state using a GTP-regeneration system
More LessIn vitro polymerization of the essential bacterial cell division protein FtsZ, in the presence of GTP, is rapid and transient due to its efficient binding and hydrolysis of GTP. In contrast, the in vivo polymeric FtsZ structure which drives cell division – the Z-ring – is present in cells for extended periods of time whilst undergoing constant turnover of FtsZ. It is demonstrated that dynamic polymerization of Escherichia coli FtsZ in vitro is sensitive to the ratio of GTP to GDP concentration. Increase of GDP concentration in the presence of a constant GTP concentration reduces both the duration of FtsZ polymerization and the initial light-scattering maximum which occurs upon addition of GTP. It is also demonstrated that by use of a GTP-regeneration system, polymers of FtsZ can be maintained in a steady state for up to 85 min, while preserving their dynamic properties. The authors therefore present the use of a GTP-regeneration system for FtsZ polymerization as an assay more representative of the in vivo situation, where FtsZ polymers are subject to a constant, relatively high GTP to GDP ratio.
-
-
-
fur-independent regulation of the Pasteurella multocida hbpA gene encoding a haemin-binding protein
Treatment of bacterial cultures with chelating agents such as 2,2′-dipyridyl (DPD) induces expression of iron-regulated genes. It is known that in the γ-Proteobacteria, the Fur protein is the major regulator of genes encoding haem- or haemoglobin-binding proteins. Electrophoretic analysis of outer-membrane proteins of the γ-proteobacterium Pasteurella multocida has revealed the induction of two proteins of 60 and 40 kDa in DPD-treated cultures in both wild-type and fur-defective strains. These two proteins have the same N-terminal amino acid sequence, which identifies this protein as the product of the PM0592 ORF. Analysis of the sequence of this ORF, which encodes a protein of 60 kDa, revealed the presence of a hexanucleotide (AAAAAA) at which a programmed translational frameshift can occur giving rise to a 40 kDa protein. Analyses conducted in Escherichia coli, using the complete PM0592 ORF and a derivative truncated at the hexanucleotide position, have shown that both polypeptides bind haemin. For this reason, the PM0592 ORF product has been designated HbpA (for haemin-binding protein). Expression studies using both RT-PCR and lacZ fusions, as well as electrophoretic profiles of outer-membrane protein composition, have demonstrated that the hbpA gene is negatively regulated by iron, manganese and haemin through a fur-independent pathway. Despite the fact that serum of mice infected with P. multocida contained antibodies that reacted with both the 60 and 40 kDa products of the hbpA gene, these proteins did not offer protection when used in immunization assays against this micro-organism.
-
- Biodiversity And Evolution
-
-
-
Comparative gene genealogical analyses of strains of serotype AD identify recombination in populations of serotypes A and D in the human pathogenic yeast Cryptococcus neoformans
More LessCryptococcus neoformans is a major pathogen of humans throughout the world. Using commercial monoclonal antibodies to capsular epitopes, strains of C. neoformans manifest five serotypes: A, B, C, D and AD. Previous studies demonstrated significant divergence among serotypes A, B, C and D, which are typically haploid. In contrast, most strains of serotype AD are diploid or aneuploid and result from recent hybridization between strains of serotypes A and D. Whether serotypes A, B, C and D represent strictly asexual lineages is not known. Using comparative genealogical analyses of two genes, the authors investigated whether recombination occurred among strains within serotypes A and D. For each of 14 serotype AD strains, a portion (642 bp) of the orotidine monophosphate pyrophosphorylase (URA5) gene was cloned and sequenced. Each of these 14 strains contained two different alleles and sequences for both alleles were obtained. The URA5 gene genealogy was compared to that derived from the laccase (LAC) gene, which was reported recently for the same 14 strains. For both genes, each of the 14 serotype AD strains contained two phylogenetically distinct alleles: one allele was highly similar to those from serotype A strains and the other to alleles from serotype D strains. However, within both the serotype A allelic group and the serotype D allelic group, there was significant incongruence between genealogies derived from URA5 and LAC. The results suggest recombination in natural populations of both serotypes A and D.
-
-
- Environmental Microbiology
-
-
-
pGIL01, a linear tectiviral plasmid prophage originating from Bacillus thuringiensis serovar israelensis
More LessBacillus thuringiensis serovar israelensis harbours, in addition to several circular plasmids, a small linear molecule of about 15 kb. Sequence analysis of this molecule, named pGIL01, showed the presence of at least 30 ORFs, five of which displayed similarity with proteins involved in phage systems: a B-type family DNA polymerase, a LexA-like repressor, two potential muramidases and a DNA-packaging protein (distantly related to the P9 protein of the tectiviral phage PRD1). Experimental evidence confirmed that pGIL01 indeed corresponds to the linear prophage of a temperate phage. This bacteriophage, named GIL01, produces small turbid plaques and is sensitive to organic solvents, which suggests the presence of lipid components in its capsid. Experiments using proteases and exonucleases also revealed that proteins are linked to the genomes of both pGIL01 prophage and GIL01 phage at their 5′ extremities. Altogether, these features are reminiscent of those of phages found in the Tectiviridae family, and more specifically of those of PRD1, a broad-host-range phage of Gram-negative bacteria. Dot-blot hybridization, PFGE, PCR and RFLP analyses also showed the presence of pGIL01 variants in the Bacillus cereus group.
-
-
- Genes And Genomes
-
-
-
Identification and functional expression of ctaA, a P-type ATPase gene involved in copper trafficking in Trametes versicolor
More LessHere the identification and characterization of a gene encoding a copper-trafficking enzyme, ctaA (copper-transporting ATPase), from the basidiomycete Trametes versicolor are described. This P-type copper ATPase gene has two alleles, differing primarily in the length of the second, unusually long intron, and encodes a 983 aa protein with 40 % sequence identity to yeast Ccc2p. Overexpression of ctaA in yeast grown in the presence of copper led to a 15-fold increase in laccase yields, while overexpression of ctaA and tahA, a previously identified copper homeostasis gene of T. versicolor, was additive, leading to a 20-fold increase in laccase production. In T. versicolor, overexpression of ctaA and tahA led to an eightfold increase in laccase expression, and a cotransformant still expressed laccase at 3000 μM copper when hardly any laccase activity is detected in the wild-type strain. Apparently, at low to moderate levels of copper tahA and ctaA overexpression disturbs the normal hierarchy of copper distribution, resulting in more being directed to the Golgi, while with high copper amounts that normally switch on the copper detoxification processes, tahA and ctaA gene products seem to out-compete the metallothionein copper chaperones, meaning laccase is still supplied with copper. These results may lead to a better understanding of copper trafficking and the hierarchy of copper distribution in the cell, and possibly be useful for constructing laccase-overproducing strains for biotechnological purposes.
-
-
-
-
Identification and study of a Candida albicans protein homologous to Saccharomyces cerevisiae Ssr1p, an internal cell-wall protein
After screening of a Candida albicans genome database, the product of an ORF (IPF 3054) that has 62 % homology with Saccharomyces cerevisiae Ssr1p, an internal cell-wall protein, was identified and named CaSsr1p. The deduced amino acid sequence shows that CaSsr1p contains an N-terminal hydrophobic signal peptide, is rich in Ser and Thr amino acids and has a potential glycosylphosphatidylinositol-attachment signal. CaSsr1p is released following degradation of isolated cell walls by zymolyase (mainly a 1,3-β-glucanase) and therefore seems to be covalently linked to the β-glucan of the cell walls. Both disruption and overexpression of the CaSSR1 gene caused an increased sensitivity to calcofluor white, Congo red and zymolyase digestion. These results suggest that CaSsr1p has a structural role associated with the cell-wall β-glucan.
-
-
-
Two different thymidylate kinase gene homologues, including one that has catalytic activity, are encoded in the onion yellows phytoplasma genome
Thymidylate kinase (TMK) catalyses the phosphorylation of dTMP to form dTDP in both the de novo and salvage pathways of dTTP synthesis in both prokaryotes and eukaryotes. Two homologues of bacterial thymidylate kinase genes were identified in a genomic library of the onion yellows (OY) phytoplasma, a plant pathogen that inhabits both plant phloem and the organs of insects. Southern blotting analysis suggested that the OY genome contained one copy of the tmk-b gene and multiple copies of the tmk-a gene. Sequencing of PCR products generated by amplification of tmk-a enabled identification of three other copies of tmk-a, although the ORF in each of these was interrupted by point mutations. The proteins, TMK-a and TMK-b, encoded by the two intact genes contained conserved motifs for catalytic activity. Both proteins were overexpressed as fusion proteins with a polyhistidine tag in Escherichia coli and purified, and TMK-b was shown to have thymidylate kinase activity. This is believed to be the first report of the catalytic activity of a phytoplasmal protein, and the OY phytoplasma is the first bacterial species to be found to have two intact homologues of tmk in its genome.
-
-
-
Nitrogen fixation genetics and regulation in a Pseudomonas stutzeri strain associated with rice
More LessThe Pseudomonas stutzeri strain A1501 (formerly known as Alcaligenes faecalis) fixes nitrogen under microaerobic conditions in the free-living state and colonizes rice endophytically. The authors characterized a region in strain A1501, corresponding to most of the nif genes and the rnf genes, involved in electron transport to nitrogenase in Rhodobacter capsulatus. The region contained three groups of genes arranged in the same order as in Azotobacter vinelandii: (1) nifB fdx ORF3 nifQ ORF5 ORF6; (2) nifLA-rnfABCDGEF-nifY2/nafY; (3) ORF13 ORF12-nifHDK-nifTY ORF1 ORF2-nifEN. Unlike in A. vinelandii, where these genes are not contiguous on the chromosome, but broken into two regions of the genome, the genes characterized here in P. stutzeri are contiguous and present on a 30 kb region in the genome of this organism. Insertion mutagenesis confirmed that most of the nif and the rnf genes in A1501 were essential for nitrogen fixation. Using lacZ fusions it was found that nif and rnf gene expression was under the control of ntrBC, nifLA and rpoN and that the rnf gene products were involved in the regulation of the nitrogen fixation process.
-
- Pathogens And Pathogenicity
-
-
-
Cord factor trehalose 6,6′-dimycolate (TDM) mediates trafficking events during mycobacterial infection of murine macrophages
More LessThe persistence of tuberculosis within pulmonary granulomatous lesions is a complex phenomenon, with bacterial survival occurring in a focal region of high immune activity. In part, the survival of the organism may be linked to the ability of the surface glycolipid trehalose 6,6′-dimycolate (TDM; cord factor) to inhibit fusion events between phospholipid vesicles inside the host macrophage. At the same time, TDM contributes to macrophage activation and a cascade of events required for initiation and maintenance of granulomatous responses. This allows increased sequestration of organisms and further survival and persistence within host tissues. Bacterial viability, macrophage cytokine and chemokine response, and intracellular trafficking were investigated in Mycobacterium tuberculosis from which TDM had been removed. Removal of surface lipids led to enhanced trafficking of organisms to acidic compartments; reconstitution of delipidated organisms with either pure TDM or the petroleum ether extract containing crude surface lipids restored normal responses. Use of TDM-coated polystyrene beads demonstrated that TDM can mediate intracellular trafficking events, as well as influence macrophage production of pro-inflammatory molecules. Thus, the presence of TDM may be an important determinant for successful infection and survival of M. tuberculosis within macrophages.
-
-
-
-
The Mycobacterium avium subsp. paratuberculosis 35 kDa protein plays a role in invasion of bovine epithelial cells
More LessMycobacterium avium subsp. paratuberculosis (M. paratuberculosis) enters intestinal epithelial cells of cattle and other ruminants via a mechanism that remains to be fully elucidated. This study showed that a gene encoding the M. paratuberculosis 35 kDa major membrane protein (MMP) is expressed at a higher level in low-oxygen and high-osmolarity conditions that are similar to the environment of the intestine. In addition, cattle with Johne's disease produced antibodies against MMP, suggesting that the protein is present during infection. The gene encoding MMP was cloned and expressed as a fusion protein with the maltose-binding protein (MBP–MMP) in Escherichia coli. Rabbit antisera were raised against a M. paratuberculosis whole-cell sonicate and MMP-specific antibodies were purified from these sera by affinity chromatography. MMP was localized to the surface of M. paratuberculosis by immunoelectron microscopy and by immunoblot analysis of fractionated protein lysates. Both anti-MMP antibodies and MBP–MMP protein inhibited M. paratuberculosis invasion of cultured Madin–Darby bovine kidney cells by 30 %. In similar invasion experiments with M. paratuberculosis incubated in low oxygen tension, these antibodies and protein decreased invasion by 60 %. Collectively, these data show that the 35 kDa MMP is a surface exposed protein that plays a role in invasion of epithelial cells. The authors suggest that the MMP is a virulence factor of M. paratuberculosis that may be important in the initiation of infection in vivo.
-
-
-
Yeast two-hybrid system survey of interactions between LEE-encoded proteins of enteropathogenic Escherichia coli
More LessMany Gram-negative pathogens employ a specific secretion pathway, termed type III secretion, to deliver virulence effector proteins directly to the membranes and cytosol of host eukaryotic cells. Subsequent functions of many effector proteins delivered in this manner result in subversion of host-signalling pathways to facilitate bacterial entry, survival and dissemination to neighbouring cells and tissues. Whereas the secreted components of type III secretion systems (TTSSs) from different pathogens are structurally and functionally diverse, the structural components and the secretion apparatus itself are largely conserved. TTSSs are large macromolecular assemblies built through interactions between protein components of hundreds of individual subunits. The goal of this project was to screen, using the standard yeast two-hybrid system, pair-wise interactions between components of the enteropathogenic Escherichia coli TTSS. To this end 37 of the 41 genes encoded by the LEE pathogenicity island were cloned into both yeast two-hybrid system vectors and all possible permutations of interacting protein pairs were screened for. This paper reports the identification of 22 novel interactions, including interactions between inner-membrane structural TTSS proteins; between the type III secreted translocator protein EspD and structural TTSS proteins; between established and putative chaperones and their cognate secreted proteins; and between proteins of undefined function.
-
-
-
An extracellular zinc metalloprotease gene of Burkholderia cepacia
More LessBurkholderia cepacia produces at least one extracellular zinc metalloprotease that may be involved in virulence. A B. cepacia zinc metalloprotease gene was cloned using a Burkholderia pseudomallei zinc metalloprotease gene as a probe. The predicted amino acid sequences of these B. cepacia and a B. pseudomallei extracellular zinc metalloproteases indicate that they are similar to the thermolysin-like family of metalloproteases (M4 family of metalloendopeptidases) and they are likely to be secreted via the general secretory pathway. zmpA isogenic mutants were constructed in B. cepacia genomovar III strains Pc715j and K56-2 by insertional inactivation of the zmpA genes. The zmpA mutants produced less protease than the parent strains. The B. cepacia strain K56-2 zmpA mutant was significantly less virulent than its parent strain in a chronic respiratory infection model; however, there was no difference between the virulence of B. cepacia strain Pc715j and a Pc715j zmpA mutant. The results indicate that this extracellular zinc metalloprotease may play a greater role in virulence in some strains of B. cepacia.
-
-
-
Alteration of DNA adenine methylase (Dam) activity in Pasteurella multocida causes increased spontaneous mutation frequency and attenuation in mice
Pasteurella multocida is one of the primary bacterial pathogens associated with bovine respiratory disease (BRD) complex. Relatively few virulence factors of P. multocida have been characterized, and there is a need for improved vaccines for prevention of BRD. In other Gram-negative species, DNA adenine methylase (Dam) regulates the expression of virulence genes, and appropriate expression of Dam is required for virulence. In this study, the authors cloned and sequenced the P. multocida A1 dam gene and demonstrated that it is able to restore Dam function in an Escherichia coli dam mutant. When P. multocida dam was placed under the control of a constitutively expressed promoter on a plasmid, it caused an increased spontaneous mutation rate in P. multocida. In addition, the plasmid-mediated alteration of Dam production in P. multocida caused it to be highly attenuated in mice. These findings indicate that appropriate expression of Dam is required for virulence of P. multocida, which is believed to be the first report that Dam is required for virulence of a species in the Pasteurellaceae. Therefore, Dam may function as a virulence gene regulator in the Pasteurellaceae, similar to previously reported findings from other Gram-negative species.
-
-
-
Mutation of lasA and lasB reduces Pseudomonas aeruginosa invasion of epithelial cells
Pseudomonas aeruginosa is an opportunistic bacterial pathogen implicated in a variety of devastating conditions. Its flexibility as a pathogen is attributed to a myriad of virulence factors and regulatory elements that respond to prevailing environmental conditions. ExoS and ExoT are type III secreted effector proteins, regulated by the transcriptional activator ExsA, that can inhibit invasion of epithelial cells by cytotoxic strains of P. aeruginosa. This study sought to understand why invasive strains, which can secrete both ExoS and ExoT, still invade epithelial cells. The results showed that LasA and elastase (LasB), which are regulated by the Las and Rhl quorum-sensing systems, modulated P. aeruginosa invasion. Mutation of lasA and/or lasB reduced P. aeruginosa invasion, which was not fully restored by extracellularly added LasB, P. aeruginosa conditioned medium containing LasA and LasB, or EGTA pretreatment of cells. This indicated that protease effects on invasion involved factors additional to tight junction disruption and subsequent alterations to cell polarity. Upon mutation of lasA and/or lasB, steady-state levels of ExoS and ExoT were increased in culture medium of P. aeruginosa grown under conditions stimulatory for these toxins. The increase in ExoS was significantly correlated with reduced invasion. In vitro experiments showed that purified LasB degraded recombinant ExoS. Taken together, these studies suggest a mechanism by which invasive strains can synthesize inhibitors of invasion, ExoS and ExoT, yet still invade epithelial cells. By this mechanism, LasA and LasB decrease the levels of the toxins directly or indirectly, and thus reduce inhibition of invasion.
-
- Physiology
-
-
-
Physiological role of S-formylglutathione hydrolase in C1 metabolism of the methylotrophic yeast Candida boidinii
More LessThe methylotrophic yeast Candida boidinii exhibits S-formylglutathione hydrolase activity (FGH, EC 3.1.2.12), which is involved in the glutathione-dependent formaldehyde oxidation pathway during growth on methanol as the sole carbon source. The structural gene, FGH1, was cloned from C. boidinii, and its predicted amino acid sequence showed more than 60 % similarity to those of FGHs from Paracoccus denitrificans and Saccharomyces cerevisiae, and human esterase D. FGH from C. boidinii contained a C-terminal tripeptide, SKL, which is a type I peroxisome-targeting signal, and a bimodal distribution of FGH between peroxisomes and the cytosol was demonstrated. The FGH1 gene was disrupted in the C. boidinii genome by one-step gene disruption. The fgh1Δ strain was still able to grow on methanol as a carbon source under methanol-limited chemostat conditions with low dilution rates (D<0·05 h−1), conditions under which a strain with disruption of the gene for formaldehyde dehydrogenase (another enzyme involved in the formaldehyde oxidation pathway) could not survive. These results suggested that FGH is not essential but necessary for optimal growth on methanol. This is believed to be the first report of detailed analyses of the FGH1 gene in a methylotrophic yeast strain.
-
-
-
-
rhlA is required for the production of a novel biosurfactant promoting swarming motility in Pseudomonas aeruginosa: 3-(3-hydroxyalkanoyloxy)alkanoic acids (HAAs), the precursors of rhamnolipids
More LessPseudomonas aeruginosa produces extracellular glycolipids composed of l-rhamnose and 3-hydroxyalkanoic acid called rhamnolipids. Although these compounds are usually regarded as biosurfactants or haemolysins, their exact physiological function is not well understood. Rhamnolipids are synthesized by a rhamnosyltransferase, encoded by the rhlAB operon, which catalyses the transfer of TDP-l-rhamnose to 3-(3-hydroxyalkanoyloxy)alkanoic acid (HAA) moieties of various lengths. RhlB is the catalytic protein of the rhamnosyltransferase. rhlA is indispensable for rhamnolipid synthesis, but its function is unknown. Using a liquid chromatography/mass spectrometry method, the production of extracellular HAAs by P. aeruginosa was detected previously and it was demonstrated that they are the actual precursors of rhamnolipid biosynthesis. In this report, evidence is presented indicating that rhlA is required for production of HAAs and that these HAAs display potent surface-active properties. P. aeruginosa can colonize surfaces by swarming motility, a form of organized translocation requiring the production of wetting agents. Using rhlA and rhlB mutants it was observed that swarming requires the expression of the rhlA gene but does not necessitate rhamnolipid production, as HAAs act as surfactants. Finally, it was shown that the use of ammonium instead of nitrate as source of nitrogen and an excess of available iron both decrease rhlA expression and swarming motility.
-
-
-
Effect of EDTA on Salmonella enterica serovar Typhimurium involves a component not assignable to lipopolysaccharide release
More LessThe effect of EDTA on Salmonella enterica serovar Typhimurium was studied in different growth phases with cells grown with or without Ca2+ and Mg2+ supplementation. EDTA affected the outer membrane much more strongly in the early exponential phase than in the mid- or late exponential phase, as indicated by uptake of 1-N-phenylnaphthylamine (a nonpolar hydrophobic probe, M r 219), and detergent (SDS) susceptibility. This effect was, however, not paralleled by LPS release (determined by measuring LPS-specific fatty acids or 14C-labelled LPS in cell-free supernatants, per a standardized cell density), which remained unchanged as a function of the growth curve. The conclusion from these results is that in the early exponential phase the effect of EDTA in S. enterica involves a component that is independent of LPS release.
-
-
-
l-Serine, d- and l-proline and alanine as respiratory substrates of Helicobacter pylori: correlation between in vitro and in vivo amino acid levels
Helicobacter pylori whole cells showed high rates of oxygen uptake with l-serine and l-proline as respiratory substrates, and somewhat lower rates with d-alanine and d-proline. These respiratory activities were inhibited by rotenone and antimycin A at low concentrations. Since pyruvate was produced from l-serine and d- and l-alanine in whole cells, the respiratory activities with these amino acids as substrates occurred via pyruvate. Whole cells showed 2,6-dichlorophenolindophenol (DCIP)-reducing activities with d- and l-proline and d-alanine as substrates, suggesting that hydrogen removed from these amino acids also participated in oxygen uptake by the whole cells. High amounts of l-proline, d- and l-alanine, and l-serine were present in H. pylori cells, and these amino acids also predominated in samples of human gastric juice. H. pylori seems to utilize d- and l-proline, d-alanine and l-serine as important energy sources in its habitat of the mucous layer of the stomach.
-
-
-
Cholic acid accumulation and its diminution by short-chain fatty acids in bifidobacteria
More LessCholic acid (CA) transport was investigated in nine intestinal Bifidobacterium strains. Upon energization with glucose, all of the bifidobacteria accumulated CA. The driving force behind CA accumulation was found to be the transmembrane proton gradient (ΔpH, alkaline interior). The levels of accumulated CA generally coincided with the theoretical values, which were calculated by the Henderson–Hasselbalch equation using the measured internal pH values of the bifidobacteria, and a pK a value of 6·4 for CA. These results suggest that the mechanism of CA accumulation is based on the diffusion of a hydrophobic weak acid across the bacterial cell membrane, and its dissociation according to the ΔpH value. A mixture of short-chain fatty acids (acetate, propionate and butyrate) at the appropriate colonic concentration (117 mM in total) reduced CA accumulation in Bifidobacterium breve JCM 1192T. These short-chain fatty acids, which are weak acids, reduced the ΔpH, thereby decreasing CA accumulation in a dose-dependent manner. The bifidobacteria did not alter or modify the CA molecule. The probiotic potential of CA accumulation in vivo is discussed in relation to human bile acid metabolism.
-
-
-
Phenotypic characterization of overexpression or deletion of the Escherichia coli crcA, cspE and crcB genes
More LessThe authors have previously shown that overexpression of the Escherichia coli K-12 crcA, cspE and crcB genes protects the chromosome from decondensation by camphor. In this study they examine the phenotypic consequences of deleting or overexpressing crcA, cspE and crcB. Overexpressing crcA, cspE and crcB increases supercoiling levels of plasmids in wild-type cells and in temperature-sensitive (Ts) gyrase mutants, suppresses the sensitivity of gyrase and topoisomerase IV (topo IV) Ts mutants to nalidixic acid, makes gyrase and topo IV Ts mutants more resistant to camphor and corrects the nucleoid morphology defects in topo IV Ts mutants. Overexpression of crcA, cspE and crcB results in a slight (2·2-fold) activation of the rcsA gene. Deleting crcA, cspE and crcB is not lethal to cells but results in an increase in sensitivity to camphor. Deletion of crcA, cspE and crcB exacerbates the nucleoid morphology defects of the topo IV Ts mutants. When the individual crcA, cspE or crcB genes were tested for their effects on camphor resistance and regulation of rcsA, cspE alone conferred 10-fold camphor resistance and 1·7-fold activation of rcsA. These activities were augmented when crcB was overexpressed with cspE (100-fold camphor resistance and 2·1-fold induction of rcsA).
-
-
-
Glucose uptake in germinating Aspergillus nidulans conidia: involvement of the creA and sorA genes
More Lessd-Glucose uptake in germinating wild-type Aspergillus nidulans conidia is an energy-requiring process mediated by at least two transport systems of differing affinities for glucose: a low-affinity system (K m∼1·4 mM) and a high-affinity system (K m∼16 μM). The low-affinity system is inducible by glucose; the high-affinity system is subject to glucose repression effected by the carbon catabolite repressor CreA and is absent in sorA3 mutant conidia, which exhibit resistance to l-sorbose toxicity. An intermediate-affinity system (K m∼400 μM) is present in sorA3 conidia germinating in derepressing conditions. creA derepressed mutants show enhanced sensitivity to l-sorbose. The high-affinity uptake system appears to be responsible for the uptake of this toxic sugar.
-
- Plant-Microbe Interactions
-
-
-
Novel bacteria degrading N-acylhomoserine lactones and their use as quenchers of quorum-sensing-regulated functions of plant-pathogenic bacteria
Bacteria degrading the quorum-sensing (QS) signal molecule N-hexanoylhomoserine lactone were isolated from a tobacco rhizosphere. Twenty-five isolates degrading this homoserine lactone fell into six groups according to their genomic REP-PCR and rrs PCR-RFLP profiles. Representative strains from each group were identified as members of the genera Pseudomonas, Comamonas, Variovorax and Rhodococcus. All these isolates degraded N-acylhomoserine lactones other than the hexanoic acid derivative, albeit with different specificity and kinetics. One of these isolates, Rhodococcus erythropolis strain W2, was used to quench QS-regulated functions of other microbes. In vitro, W2 strongly interfered with violacein production by Chromobacterium violaceum, and transfer of pathogenicity in Agrobacterium tumefaciens. In planta, R. erythropolis W2 markedly reduced the pathogenicity of Pectobacterium carotovorum subsp. carotovorum in potato tubers. These series of results reveal the diversity of the QS-interfering bacteria in the rhizosphere and demonstrate the validity of targeting QS signal molecules to control pathogens with natural bacterial isolates.
-
-
Volumes and issues
-
Volume 170 (2024)
-
Volume 169 (2023)
-
Volume 168 (2022)
-
Volume 167 (2021)
-
Volume 166 (2020)
-
Volume 165 (2019)
-
Volume 164 (2018)
-
Volume 163 (2017)
-
Volume 162 (2016)
-
Volume 161 (2015)
-
Volume 160 (2014)
-
Volume 159 (2013)
-
Volume 158 (2012)
-
Volume 157 (2011)
-
Volume 156 (2010)
-
Volume 155 (2009)
-
Volume 154 (2008)
-
Volume 153 (2007)
-
Volume 152 (2006)
-
Volume 151 (2005)
-
Volume 150 (2004)
-
Volume 149 (2003)
-
Volume 148 (2002)
-
Volume 147 (2001)
-
Volume 146 (2000)
-
Volume 145 (1999)
-
Volume 144 (1998)
-
Volume 143 (1997)
-
Volume 142 (1996)
-
Volume 141 (1995)
-
Volume 140 (1994)
-
Volume 139 (1993)
-
Volume 138 (1992)
-
Volume 137 (1991)
-
Volume 136 (1990)
-
Volume 135 (1989)
-
Volume 134 (1988)
-
Volume 133 (1987)
-
Volume 132 (1986)
-
Volume 131 (1985)
-
Volume 130 (1984)
-
Volume 129 (1983)
-
Volume 128 (1982)
-
Volume 127 (1981)
-
Volume 126 (1981)
-
Volume 125 (1981)
-
Volume 124 (1981)
-
Volume 123 (1981)
-
Volume 122 (1981)
-
Volume 121 (1980)
-
Volume 120 (1980)
-
Volume 119 (1980)
-
Volume 118 (1980)
-
Volume 117 (1980)
-
Volume 116 (1980)
-
Volume 115 (1979)
-
Volume 114 (1979)
-
Volume 113 (1979)
-
Volume 112 (1979)
-
Volume 111 (1979)
-
Volume 110 (1979)
-
Volume 109 (1978)
-
Volume 108 (1978)
-
Volume 107 (1978)
-
Volume 106 (1978)
-
Volume 105 (1978)
-
Volume 104 (1978)
-
Volume 103 (1977)
-
Volume 102 (1977)
-
Volume 101 (1977)
-
Volume 100 (1977)
-
Volume 99 (1977)
-
Volume 98 (1977)
-
Volume 97 (1976)
-
Volume 96 (1976)
-
Volume 95 (1976)
-
Volume 94 (1976)
-
Volume 93 (1976)
-
Volume 92 (1976)
-
Volume 91 (1975)
-
Volume 90 (1975)
-
Volume 89 (1975)
-
Volume 88 (1975)
-
Volume 87 (1975)
-
Volume 86 (1975)
-
Volume 85 (1974)
-
Volume 84 (1974)
-
Volume 83 (1974)
-
Volume 82 (1974)
-
Volume 81 (1974)
-
Volume 80 (1974)
-
Volume 79 (1973)
-
Volume 78 (1973)
-
Volume 77 (1973)
-
Volume 76 (1973)
-
Volume 75 (1973)
-
Volume 74 (1973)
-
Volume 73 (1972)
-
Volume 72 (1972)
-
Volume 71 (1972)
-
Volume 70 (1972)
-
Volume 69 (1971)
-
Volume 68 (1971)
-
Volume 67 (1971)
-
Volume 66 (1971)
-
Volume 65 (1971)
-
Volume 64 (1970)
-
Volume 63 (1970)
-
Volume 62 (1970)
-
Volume 61 (1970)
-
Volume 60 (1970)
-
Volume 59 (1969)
-
Volume 58 (1969)
-
Volume 57 (1969)
-
Volume 56 (1969)
-
Volume 55 (1969)
-
Volume 54 (1968)
-
Volume 53 (1968)
-
Volume 52 (1968)
-
Volume 51 (1968)
-
Volume 50 (1968)
-
Volume 49 (1967)
-
Volume 48 (1967)
-
Volume 47 (1967)
-
Volume 46 (1967)
-
Volume 45 (1966)
-
Volume 44 (1966)
-
Volume 43 (1966)
-
Volume 42 (1966)
-
Volume 41 (1965)
-
Volume 40 (1965)
-
Volume 39 (1965)
-
Volume 38 (1965)
-
Volume 37 (1964)
-
Volume 36 (1964)
-
Volume 35 (1964)
-
Volume 34 (1964)
-
Volume 33 (1963)
-
Volume 32 (1963)
-
Volume 31 (1963)
-
Volume 30 (1963)
-
Volume 29 (1962)
-
Volume 28 (1962)
-
Volume 27 (1962)
-
Volume 26 (1961)
-
Volume 25 (1961)
-
Volume 24 (1961)
-
Volume 23 (1960)
-
Volume 22 (1960)
-
Volume 21 (1959)
-
Volume 20 (1959)
-
Volume 19 (1958)
-
Volume 18 (1958)
-
Volume 17 (1957)
-
Volume 16 (1957)
-
Volume 15 (1956)
-
Volume 14 (1956)
-
Volume 13 (1955)
-
Volume 12 (1955)
-
Volume 11 (1954)
-
Volume 10 (1954)
-
Volume 9 (1953)
-
Volume 8 (1953)
-
Volume 7 (1952)
-
Volume 6 (1952)
-
Volume 5 (1951)
-
Volume 4 (1950)
-
Volume 3 (1949)
-
Volume 2 (1948)
-
Volume 1 (1947)