- Volume 139, Issue 10, 1993
Volume 139, Issue 10, 1993
- Physiology And Growth
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Proteolysis and orientation in Dictyostelium slugs
More LessSUMMARY: It has been long known that the migrating slugs of the cellular slime moulds are highly sensitive to their environment and orient towards light and in temperature and chemical gradients. There is considerable evidence from past work that these orientations are governed by NH3 which affects the rate of movement of cells within the slug with such precision that orientation to the external stimuli is achieved. In order to test this hypothesis further, various ways to alter the internal NH3 concentration were devised. Substances that either increased or decreased proteolysis were applied to one side of the tip of a slug, thereby affecting its orientation. Some of the treatments strongly support the role of internally produced NH3 in orientation, and all the treatments produce results that are consistent with the hypothesis.
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Protection by sterols against the cytotoxicity of syringomycin in the yeast Saccharomyces cereuisiae
More LessSUMMARY: A brief exposure (ca 20 min) of the yeast Saccharomyces cerevisiae to the phytotoxin syringomycin was sufficient to kill the cell. The protective effect of sterols against this cytotoxicity of syringomycin was investigated. Syringomycin was much more toxic to growing cells than to stationary-phase cells. The cytotoxicity of syringomycin was reduced in an environment containing sterols. Cytotoxicity of syringomycin at 3 fig ml-1 (ca 2.5 μm) was completely abolished by the simultaneous presence of 10 μM-cholesterol in the medium. Cholesterol acetate had no protective effect. Ergosterol, sitosterol and stigmasterol also protected against syringomycin, but they were less effective than cholesterol. The protective effect of sterols against the action of syringomycin is consistent with our hypothesis that membrane ergosterol is a critical component for syringomycin-binding as suggested by recent genetic studies.
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Growth-phase-dependent expression of the lipolytic system of Acinetobacter calcoaceticus BD413: cloning of a gene encoding one of the esterases
More LessSUMMARY: Acinetobacter calcoaceticus BD413, when grown in batch culture in nutrient broth, produces both extracellular lipase activity and cell-bound esterase activity during and after the transition between exponential growth and the stationary phase. From a library of A. calcoaceticus DNA in Escherichia coli, plasmids were isolated that enabled E. coli to grow on media with tributyrin as the sole carbon source. Assays with model substrates classified the product of the cloned gene as an esterase. Via deletion analysis, the esterase gene was mapped on a 1.8 kbp chromosomal DNA fragment. This fragment was sequenced and found to contain one open reading frame, termed estA, which encodes a protein of 40.0 kDa. The amino acid sequence of this protein shows homology to a number of lipolytic enzymes, most notably to esterases. Deletion of estA only partially abolished cell-bound esterase activity in A. calcoaceticus, indicating that BD413 forms at least two esterases. Both esterases show the same temporal regulation of expression. β-Galactosidase activity was measured in strains in which a promoterless lacZ gene was inserted into estA. Induction of lacZ expression in these strains also occurred at the end of exponential growth in batch cultures, indicating that production of the esterase is regulated at the genetic level.
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Formation of melanin pigment by a mutant of Bacillus thuringiensis H-14
More LessSUMMARY: A mutant of Bacillus thuringiensis H-14 produced a dark brown pigment during sporulation. Production of the pigment depended on the nutritional properties of the growth medium. The pigment was identified as melanin, based on chemical tests and its infra-red spectrum. Incorporation of L-tyrosine in the culture medium enhanced the level of melanin production, and L-3,4-dihydroxyphenylalanine (L-DOPA) was detected in the culture broth during the late-exponential phase of growth. This indicates that the pathway of melanin synthesis is from L-tyrosine, via L-DOPA, to melanin.
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A halophilic thermophilic bacterium isolated from a coastal hot spring in Lutao, Taiwan
More LessSUMMARY: A heterotrophic, moderately thermophilic bacterial strain, designated strain T501, was isolated from a hot spring on the coast of Lutao, Taiwan. This bacterial strain was a strictly aerobic, Gram-negative rod, normally 0.6-0.7 m in diameter and 4-10 m in length, and motility was achieved by one to several lateral flagella. Its minimum and maximum growth temperatures were approximately 30 and 60 C, respectively, with an optimal temperature at about 50 C. The G + C ratio of its DNA was 38.1 mol%. Strain T501 tolerated a pH range from 6 to 9. It was halophilic, growing optimally in about 2% (w/v) salt, and Na+ was indispensable unless Mg2+ or Ca2+ were available. The addition of either cation to Na--sufficient media significantly enhanced growth. Halophilic heterotrophic bacteria capable of aerobic growth over a temperature range of 40-55 C have not been reported previously.
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- Systematics
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Helicobacter canis sp. nov., a new species from dogs: an integrated study of phenotype and genotype
SUMMARY: A group of Campylobacter-like organisms (CLOs) were isolated from the faeces of diarrhoeic or healthy dogs, constituting 4% of all CLOs from this source. Since they formed a unique DNA homology group within the genus Helicobacter, and exhibited distinctive phenotypic properties, they were collectively termed the HC group. A polyphasic taxonomic analysis was made of this group. The phenotype of four dog isolates and a single human isolate was unique and could be distinguished bacteriologically from other helicobacters. Electron microscopic ultrastructure revealed defining characteristics of Helicobacter. The 16S rRNA gene of the nominated type strain NCTC 12739T was sequenced, and its analysis delineated the group as a new species of Helicobacter. This conclusion was supported by relative DNA homology and whole-cell protein electrophoretic patterns. We therefore propose the name Helicobacter canis sp. nov. for this group. The species most closely related to H. canis sp. nov. were H. cinaedi, ‘Flexispira rappini’ and H. fennelliae. A species-specific recombinant DNA probe was cloned from NCTC 12739T for use in routine laboratory identification and epidemiological studies. The faecal source, bile tolerance and lack of urease activity of H. canis sp. nov. suggest that this new Helicobacter species colonizes the lower bowel rather than the stomach.
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- Genome Analysis
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“Analysis of the Anaplasma mavginale genome by pulsed-field electrophoresis”
More LessSUMMARY: Anaplasma marginale is a rickettsial parasite of bovine erythrocytes causing world-wide economic losses in livestock production. Despite its importance, little is known about this rickettsia at a molecular level because it has not been cultured in vitro, and there is no small-animal model. Although several genes have been cloned and sequenced, the gross genome structure of the organism has not yet been well characterized. We separated intact bovine erythrocytes from leucocytes, and determined the genome size of A. marginale by use of restriction endonuclease cleavage and pulsed-field gel electrophoresis (PFGE). A value of 56 mol% G + C was obtained for this genome by spectral analysis. Undigested A. marginale DNA failed to migrate under several different electrophoretic conditions, indicating a circular genome. Digestions of intact A. marginale DNA were performed using restriction endonucleases NotI, SfiI and PacI. Complete digestion with SfiI resulted in 12 distinct bands ranging in size from 14 to 170 kbp. Total size determined by addition of SfiI-digested fragments was approximately 1200 kbp. PacI cleaved the A. marginale genome from three different isolates into just three fragments, of 598, 557 and 97 kbp. Incomplete digestion produced a band measuring 1250 kbp. These results indicate that A. marginale has a circular genome between 1200 and 1260 kbp, with a G + C content of 56 mol%.
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Variation in the size of the ospA-containing linear plasmid, but not the linear chromosome, among the three Borrelia species associated with Lyme disease
More LessSUMMARY: The aetiological agents of Lyme disease form a phylogenetically heterogeneous group, composed of three species, Borrelia burgdorferi, Borrelia garinii, and group VS461. We have compared the sizes of the linear plasmid that carries the genes encoding the major outer-surface proteins OspA and OspB as well as the size and structure of the chromosome among the Lyme disease spirochaetes. We have found differences in the sizes of the ospA-containing plasmids, but not the linear chromosomes among the three species. The ospA-containing plasmid size of 50 kb in B. burgdorferi isolates is significantly smaller than the size of 55 kb in B. garinii isolates and 56 kb in group VS461 isolates. The chromosome was found to be linear in all three Borrelia species, but not significantly different in size.
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