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Genomic Interrogation of the Dassie Bacillus Reveals It as a Unique RD1 Mutant within the Mycobacterium tuberculosis Complex. Serge Mostowy, 2004.Despite their remarkable genetic homology, members of the Mycobacterium tuberculosis complex express very different phenotypes, most notably in their spectra of clinical presentation . For example, M . tuberculosis is regarded as pathogenic to humans, whereas members having deleted RD1, such as Mycobacterium microti and Mycobacterium bovis BCG, are not . The dassie bacillus, an infrequent variant of the M . tuberculosis complex characterized as being most similar to M . microti, is the causative agent of tuberculosis (TB) in the dassie (Procavia capensis) . Intriguingly, the dassie bacillus is not pathogenic to rabbits or guinea pigs and has never been documented to infect humans . Although it was identified more than a half-century ago, the reasons behind its attenuation are unknown . Because large sequence polymorphisms have presented themselves as the most obvious genomic distinction among members of the M . tuberculosis complex, the DNA content of the dassie bacillus was interrogated by Affymetrix GeneChip to identify regions that are absent from it but present in M . tuberculosis H37Rv . Comparison has led to the identification of nine regions of difference (RD), five of which are shared with M . microti (RDs 3, 7, 8, 9, and 10) . Although the dassie bacillus does not share the other documented deletions in M . microti (RD1mic, RD5mic, MID1, MID2, and MID3), it has endured unique deletions in the regions of RD1, RD5, N-RD25, and Rv3081-Rv3082c (virS) . RD1das, affecting only Rv3874-Rv3877, is the smallest natural deletion of the RD1 region uncovered and points to genes within this region that are likely implicated in virulence . Newfound deletions from the dassie bacillus are discussed in relation to their evolutionary and biological significance . Localization and Functional Analysis of PepI, the Immunity Peptide of Pep5-Producing Staphylococcus epidermidis Strain 5. Anja Hoffmann, 2004.Pep5 is a cationic pore-forming lantibiotic produced by Staphylococcus epidermidis strain 5 . The producer strain protects itself from the lethal action of its own bacteriocin through the 69-amino-acid immunity peptide PepI . The N-terminal segment of PepI contains a 20-amino-acid stretch of apolar residues, whereas the C terminus is very hydrophilic, with a net positive charge . We used green fluorescent protein (GFP)-PepI fusions to obtain information on its localization in vivo . PepI was found to occur outside the cytoplasm and to accumulate at the membrane-cell wall interface . The extracellular localization appeared essential for conferring immunity . We analyzed the functional role of the specific segments by constructing various mutant peptides, which were also fused to GFP . When the hydrophobic N-terminal segment of PepI was disrupted by introducing charged amino acids, the export of PepI was blocked and clones expressing such mutant peptides were Pep5 sensitive . When PepI was successively shortened at the C terminus, in contrast, its export properties remained unchanged whereas its ability to confer immunity was gradually reduced . The results show that the N-terminal part is required for the transport of PepI and that the C-terminal part is important for conferring the immunity phenotype . A concept based on target shielding is proposed for the PepI immunity mechanism . Further Evidence that a Cell Wall Precursor [C55-MurNAc-(Peptide)-GlcNAc] Serves as an Acceptor in a Sorting Reaction. Alexey Ruzin, 2002.Previous studies suggested that a Gly-containing branch of cell wall precursor [C55-MurNAc-(peptide)-GlcNAc], which is often referred to as lipid II, might serve as a nucleophilic acceptor in sortase-catalyzed anchoring of surface proteins in Staphylococcus aureus. To test this hypothesis, we first simplified the procedure for in vitro biosynthesis of Gly-containing lipid II by using branched UDP-MurNAc-hexapeptide isolated from the cytoplasm of Streptomyces spp . Second, we designed a thin-layer chromatography-based assay in which the mobility of branched but not linear lipid II is shifted in the presence of both sortase and LPSTG-containing peptide . These results and those of additional experiments presented in this study further suggest that lipid II indeed serves as a natural substrate in a sorting reaction . Cellulosomes from Mesophilic Bacteria. Roy H. Doi, 2003.
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