Rapid β-lactam-induced lysis requires successful assembly of the cell division machinery

Abstract

␤-lactam antibiotics inhibit penicillin binding proteins (PBPs) involved in peptidoglycan synthesis. Although inhibition of peptidoglycan biosynthesis is generally thought to induce cell lysis, the pattern and mechanism of cell lysis can vary substantially. ␤-lactams that inhibit FtsI, the only division specific PBP, block cell division and result in growth as filaments. These filaments ultimately lyse through a poorly understood mechanism. Here we find that one such ␤-lactam, cephalexin, can, under certain conditions, lead instead to rapid lysis at nascent division sites through a process that requires the complete and ordered assembly of the divisome, the essential machinery involved in cell division. We propose that this assembly process (in which the localization of cell wall hydrolases depends on properly targeted FtsN, which in turn depends on the presence of FtsI) ensures that the biosynthetic machinery to form new septa is in place before the machinery to degrade septated daughter cells is enabled. ␤-lactams that target FtsI subvert this mechanism by inhibiting FtsI without perturbing the normal assembly of the cell division machinery and the consequent activation of cell wall hydrolases. One seemingly paradoxical implication of our results is that ␤-lactam therapy may be improved by promoting active cell division.amidase ͉ cell wall hydrolase ͉ ftsN ͉ penicillin-binding proteins ͉ peptidoglycan

The role of the hok/sok locus in bacterial response to stressful growth conditions

“…However, in SS996 host strains, these growing SS996 cells become more susceptible to antibiotic killing in ampicillin-selective media due to the fact that ampicillin and other β-lactam antibiotics kill only dividing cells [26]. This increased susceptibility to ampicillin was By enhancing the survival of the host cells in these unfavourable circumstances/growth conditions, the hok/sok locus would subsequently enhance the propagation of the resistance elements carried on the plasmid.…”

A Fail-Safe Mechanism in the Septal Ring Assembly Pathway Generated by the Sequential Recruitment of Cell Separation Amidases and Their Activators

“…While treatment with relatively low levels of the FtsI-specific ␤-lactam cephalexin (10 g/ml) inhibits division, treatment with higher levels (50 g/ml) or with less-specific ␤-lactams like ampicillin results in rapid cell lysis from lesions that emanate from septa (14, 22, 40, 41, 53, 57, 60). Previous studies indicate that this rapid lysis is dependent upon all of the essential cell division proteins, including FtsN, as well as the LytM factors and the amidases (14,60). AmiA appeared to be the most important amidase for rapid lysis (14), suggesting that miscoordinated AmiA activation at the septum by EnvC may be the primary lytic determinant.…”

“…Curiously, an AmiB Ϫ AmiC Ϫ double mutant does not have a strong cell separation phenotype (14), suggesting that amidase localization is dispensable for cell separation. This indicates that AmiA can largely facilitate cell separation on its own even though it does not specifically accumulate at the division site.…”

“…The periplasmic PG amidases, AmiA, AmiB, and AmiC ( Fig. 1), are required to split this shared septal PG to shape the new poles and allow constriction of the outer membrane to closely follow that of the inner membrane (14,35,49,60). Amidases are PG hydrolases that break peptide cross-links in the PG meshwork by cleaving bonds that link stem peptides to the N-acetylmuramic acid component of the glycan strands.…”

Regulation of cell size in response to nutrient availability by fatty acid biosynthesis in Escherichia coli

“…Cells were grown into early exponential phase and transferred onto agarose pads for phase-contrast imaging on an inverted Nikon TE2000-E microscope. Details of the imaging acquisition were described previously (76). Computational analysis of single-cell size is implemented in MATLAB.…”