Abstract
Bacillus mycoides is a sporogenic Gram-positive soil bacillus of the B. cereus group. This bacillus, which forms hyphal colonies, is composed of cells connected in filaments that make up bundles and turn clock- or counterclockwise depending on the strain. A thick peptidoglycan wall gives the rod cells of these bacilli strength and shape. One approach used to study peptidoglycan neoformation in Gram positives exploits the binding properties of antibiotics such as vancomycin and ramoplanin to nascent peptidoglycan, whose localization in the cell is monitored by means of a fluorescent tag. When we treated B. mycoides strains with BODIPY-vancomycin, we found the expected accumulation of fluorescence at the midcell septa and localization along the cell sidewall in small foci distributed quite uniformly. Intense fluorescence was also observed at the poles of many cells, more clearly visible at the outer edges of the cell chains. The unusual abundance of peptidoglycan intermediates at the cell poles after cell separation suggests that the construction process of this structure is different from that of B. subtilis, in which the free poles are rarely reactive to vancomycin.
Highlights
The thick cell wall of Gram-positive bacilli contains several layers of peptidoglycan (PG), a unique giant polymer of glycan strands made of alternating N-acetylglucosamine and N-acetylmuramic acid, cross-linked by peptide bridges (Vollmer et al 2008)
The minimal inhibitory concentration of Van-BDP (MIC) on B. mycoides cells was found at 2 lg/ml, while the concentration of unlabeled vancomycin required to interrupt growth was lower, that is approx. 0.2 lg/ml
Vancomycin, the so-called last-resort drug for antibioticresistant infections, is a useful tool for detecting new PG location sites in the bacterial cell wall (Daniel and Errington 2003; Tiyanont et al 2006). This antibiotic binds to the C-terminal D-Ala-D-Ala residues present in the pentapeptide of lipid II-linked disaccharides, the PG precursors, and in the un-crosslinked peptides of nascent peptidoglycan (Vollmer et al 2008)
Summary
The thick cell wall of Gram-positive bacilli contains several layers of peptidoglycan (PG), a unique giant polymer of glycan strands made of alternating N-acetylglucosamine and N-acetylmuramic acid, cross-linked by peptide bridges (Vollmer et al 2008). The PG precursors and the pentapeptides of the nascent glycan chains expose a free D-Ala-D-Ala group bound by the antibiotic vancomycin. When linked to different fluorochromes, vancomycin can be used to label, and visually detect, the spatial pattern of new PG localization within the cell. This approach has been used to detect the sites of cell wall neoformation in B. subtilis (Daniel and Errington 2003; Tiyanont et al 2006), though no such information is available for the numerous bacilli with a similar cell shape that constitute the B. cereus group (Guinebretiere et al 2008). B. mycoides was first studied by the Russian naturalist Gause (1939), who investigated the genesis of the typical colonies of these soil bacilli, whose growth on agar plates forms an attractive rhizoidal shape
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