monocytogenes is only slightly impaired when it lacks the activities of Lmo2812 or both Lmo2812 and PBP5 [11, 12]. Reduced growth rates

have also been reported for a S. pneumoniae mutant lacking functional PBP3 [24] and for a double N. gonorrhoeae mutant lacking both PBP3 and PBP4 [28]. On the other hand, no changes in growth rate were observed for E. coli or B. subtilis mutants lacking most or all of their DD-carboxypeptidase activity [27, 29]. However, the loss of Lmo2812 did result in significant changes in morphology. The mutant cells were significantly longer, slightly curved and had bent ends. These CHIR-99021 molecular weight changes were even more pronounced in the double mutant AD07 lacking both Lmo2812 and PBP5. This finding is interesting because we

did not notice any alterations selleckchem in cell shape in a L. monocytogenes mutant lacking PBP5 alone, although the cell wall of the mutant was much thicker than that of the parental strain [11, 12], even though Guinane et al. [15] did describe such changes. The differences between our observations may be due to variation in the strain (EGD versus EGDe) or growth conditions employed [15]. The reason for the prominent morphological changes in strain KD2812 is difficult to pinpoint since there do not seem to be any remarkable changes in the muropeptide structure of the peptidoglycan of this mutant. However, the observed changes in cell morphology implicate the protein in the late stages of peptidoglycan synthesis, presumably in the determination of the availability of pentapeptide substrates. Our finding that Lmo2812 preferentially degrades low-molecular-weight substrates may point to the a role for this protein triclocarban in cell wall turnover. Further Entospletinib price studies are required to

clarify the function of Lmo2812, although, as in the case of extensive studies on the D-alanine carboxypeptidases of E. coli [30] and other bacteria, they may not yield conclusive results. Conclusions The results of this study conclusively show that nine of the ten previously identified putative PBP genes of L. monocytogenes code for proteins that bind β-lactam antibiotics and their labeled or fluorescent derivatives. Eight of these proteins were identified in whole cell extracts, whereas the ninth protein, Lmo2812, was only shown to bind β-lactams following expression in E. coli and subsequent purification by affinity chromatography. The inability to detect Lmo2812 activity in the L. monocytogenes cell may be explained by the low abundance of this protein, whose expression is regulated by the two-component system CesRK [21]. We have also demonstrated that the LMM PBP Lmo2812 is a DD-carboxypeptidase and has no discernible β-lactamase activity. Mutants lacking the protein grow normally, although their cells are often longer and slightly curved. Similar morphological changes were observed in the case of a double mutant lacking two LMM carboxypeptidases: Lmo2812 and Lmo2754.