- Volume 157, Issue 11, 2011
Volume 157, Issue 11, 2011
- Physiology and Biochemistry
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VisG is essential for biosynthesis of virginiamycin S, a streptogramin type B antibiotic, as a provider of the nonproteinogenic amino acid phenylglycine
More LessA streptogramin type B antibiotic, virginiamycin S (VS), is produced by Streptomyces virginiae, together with a streptogramin type A antibiotic, virginiamycin M1 (VM), as its synergistic counterpart. VS is a cyclic hexadepsipeptide containing a nonproteinogenic amino acid, l-phenylglycine (l-pheGly), in its core structure. We have identified, in the left-hand extremity of the virginiamycin supercluster, two genes that direct VS biosynthesis with l-pheGly incorporation. Transcriptional analysis revealed that visF, encoding a nonribosomal peptide synthetase, and visG, encoding a protein with homology to a hydroxyphenylacetyl-CoA dioxygenase, are under the transcriptional regulation of virginiae butanolide (VB), a small diffusing signalling molecule that governs virginiamycin production. Gene deletion of visG resulted in complete loss of VS production without any changes in VM production, suggesting that visG is required for VS biosynthesis. The abolished VS production in the visG disruptant was fully recovered either by the external addition of pheGly or by gene complementation, which indicates that VisG is involved in VS biosynthesis as the provider of an l-pheGly molecule. A feeding experiment with l-pheGly analogues suggested that VisF, which is responsible for the last condensation step, has high substrate specificity toward l-pheGly.
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Bacillus subtilis Fur represses one of two paralogous haem-degrading monooxygenases
More LessIdentification of genes regulated by the ferric uptake regulator (Fur) protein has provided insights into the diverse mechanisms of adaptation to iron limitation. In the soil bacterium Bacillus subtilis, Fur senses iron sufficiency and represses genes that enable iron uptake, including biosynthetic and transport genes for the siderophore bacillibactin and uptake systems for siderophores produced by other organisms. We here demonstrate that Fur regulates hmoA (formerly yetG), which encodes a haem monooxygenase. HmoA is the first characterized member of a divergent group of putative monooxygenases that cluster separately from the well-characterized IsdG family. B. subtilis also encodes an IsdG family protein designated HmoB (formerly YhgC). Unlike hmoA, hmoB is constitutively expressed and not under Fur control. HmoA and HmoB both bind haemin in vitro with approximately 1 : 1 stoichiometry and degrade haemin in the presence of an electron donor. Mutational and spectroscopic analyses indicate that HmoA and HmoB have distinct active site architectures and interact differently with haem. We further show that B. subtilis can use haem as an iron source, but that this ability is independent of HmoA and HmoB.
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Lipidomics of Candida albicans biofilms reveals phase-dependent production of phospholipid molecular classes and role for lipid rafts in biofilm formation
Candida albicans-associated bloodstream infections are linked to the ability of this yeast to form biofilms. In this study, we used lipidomics to compare the lipid profiles of C. albicans biofilms and planktonic cells, in early and mature developmental phases. Our results showed that significant differences exist in lipid composition in both developmental phases. Biofilms contained higher levels of phospholipid and sphingolipids than planktonic cells (nmol per g biomass, P<0.05 for all comparisons). In the early phase, levels of lipid in most classes were significantly higher in biofilms compared to planktonic cells (P≤0.05). The ratio of phosphatidylcholine to phosphatidylethanolamine was lower in biofilms compared to planktonic cells in both early (1.17 vs 2.52, P≤0.001) and late (2.34 vs 3.81, P≤0.001) developmental phases. The unsaturation index of phospholipids decreased with time, with this effect being particularly strong for biofilms. Inhibition of the biosynthetic pathway for sphingolipid [mannosyl diinositolphosphoryl ceramide, M(IP)2C] by myriocin or aureobasidin A, and disruption of the gene encoding inositolphosphotransferase (Ipt1p), abrogated the ability of C. albicans to form biofilms. The differences in lipid profiles between biofilms and planktonic Candida cells may have important implications for the biology and antifungal resistance of biofilms.
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The glgB-encoded glycogen branching enzyme is essential for glycogen accumulation in Corynebacterium glutamicum
Corynebacterium glutamicum transiently accumulates glycogen as carbon capacitor during the early exponential growth phase in media containing carbohydrates. In some bacteria glycogen is synthesized by the consecutive action of ADP-glucose pyrophosphorylase (GlgC), glycogen synthase (GlgA) and glycogen branching enzyme (GlgB). GlgC and GlgA of C. glutamicum have been shown to be necessary for glycogen accumulation in this organism. However, although cg1381 has been annotated as the putative C. glutamicum glgB gene, cg1381 and its gene product have not been characterized and their role in transient glycogen accumulation has not yet been investigated. We show here that the cg1381 gene product of C. glutamicum catalyses the formation of α-1,6-glycosidic bonds in polysaccharides and thus represents a glycogen branching enzyme. RT-PCR experiments revealed glgB to be co-transcribed with glgE, probably encoding a maltosyltransferase. Promoter activity assays with the glgE promoter region revealed carbon-source-dependent expression of the glgEB operon. Characterization of the growth and glycogen content of glgB-deficient and glgB-overexpressing strains showed that the glycogen branching enzyme GlgB is essential for glycogen formation in C. glutamicum. Taken together these results suggest that an interplay of the enzymes GlgC, GlgA and GlgB is not essential for growth, but is required for synthesis of the transient carbon capacitor glycogen in C. glutamicum.
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