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Galactose Metabolism by Streptococcus mutans. Jacqueline Abranches, 2004.The galK gene, encoding galactokinase of the Leloir pathway, was insertionally inactivated in Streptococcus mutans UA159 . The galK knockout strain displayed only marginal growth on galactose, but growth on glucose or lactose was not affected . In strain UA159, the sugar phosphotransferase system (PTS) for lactose and the PTS for galactose were induced by growth in lactose and galactose, although galactose PTS activity was very low, suggesting that S . mutans does not have a galactose-specific PTS and that the lactose PTS may transport galactose, albeit poorly . To determine if the galactose growth defect of the galK mutant could be overcome by enhancing lactose PTS activity, the gene encoding a putative repressor of the operon for lactose PTS and phospho-ß-galactosidase, lacR, was insertionally inactivated . A galK and lacR mutant still could not grow on galactose, although the strain had constitutively elevated lactose PTS activity . The glucose PTS activity of lacR mutants grown in glucose was lower than in the wild-type strain, revealing an influence of LacR or the lactose PTS on the regulation of the glucose PTS . Mutation of the lacA gene of the tagatose pathway caused impaired growth in lactose and galactose, suggesting that galactose can only be efficiently utilized when both the Leloir and tagatose pathways are functional . A mutation of the permease in the multiple sugar metabolism operon did not affect growth on galactose . Thus, the galactose permease of S . mutans is not present in the gal, lac, or msm operons . Benzoate-Coenzyme A Ligase from Thauera aromatica: an Enzyme Acting in Anaerobic and Aerobic Pathways. Karola Schühle, 2003.In the denitrifying member of the ß-Proteobacteria Thauera aromatica, the anaerobic metabolism of aromatic acids such as benzoate or 2-aminobenzoate is initiated by the formation of the coenzyme A (CoA) thioester, benzoyl-CoA and 2-aminobenzoyl-CoA, respectively . Both aromatic substrates were transformed to the acyl-CoA intermediate by a single CoA ligase (AMP forming) that preferentially acted on benzoate . This benzoate-CoA ligase was purified and characterized as a 57-kDa monomeric protein . Based on Vmax/Km, the specificity constant for 2-aminobenzoate was 15 times lower than that for benzoate; this may be the reason for the slower growth on 2-aminobenzoate . The benzoate-CoA ligase gene was cloned and sequenced and was found not to be part of the gene cluster encoding the general benzoyl-CoA pathway of anaerobic aromatic metabolism . Rather, it was located in a cluster of genes coding for a novel aerobic benzoate oxidation pathway . In line with this finding, the same CoA ligase was induced during aerobic growth with benzoate . A deletion mutant not only was unable to grow anaerobically on benzoate or 2-aminobenzoate, but also aerobic growth on benzoate was affected . This suggests that benzoate induces a single benzoate-CoA ligase . The product of benzoate activation, benzoyl-CoA, then acts as inducer of separate anaerobic or aerobic pathways of benzoyl-CoA, depending on whether oxygen is lacking or present . Diversity and Abundance of Uncultured Cytophaga-Like Bacteria in the Delaware Estuary. David L. Kirchman, 2003.The Cytophaga-Flavobacterium group is known to be abundant in aquatic ecosystems and to have a potentially unique role in the utilization of organic material . However, relatively little is known about the diversity and abundance of uncultured members of this bacterial group, in part because they are underrepresented in clone libraries of 16S rRNA genes . To circumvent a suspected bias in PCR, a primer set was designed to amplify 16S rRNA genes from the Cytophaga-Flavobacterium group and was used to construct a library of these genes from the Delaware Estuary . This library had several novel Cytophaga-like 16S rRNA genes, of which about 40% could be grouped together into two clusters (DE clusters 1 and 2) defined by sequences initially observed only in the Delaware library; the other 16S rRNA genes were classified into an additional four clades containing sequences from other environments . An oligonucleotide probe was designed for the cluster with the most clones (DE cluster 2) and was used in fluorescence in situ hybridization assays . Bacteria in DE cluster 2 accounted for about 10% of the total prokaryotic abundance in the Delaware Estuary and in a depth profile of the Chukchi Sea (Arctic Ocean) . The presence of DE cluster 2 in the Arctic Ocean was confirmed by results from 16S rRNA clone libraries . The contribution of this cluster to the total bacterial biomass is probably larger than is indicated by the abundance of its members, because the average cell volume of bacteria in DE cluster 2 was larger than those of other bacteria and prokaryotes in the Delaware Estuary and Chukchi Sea . DE cluster 2 may be one of the more abundant bacterial groups in the Delaware Estuary and possibly other marine environments .
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