Modification of the Peptidoglycan of Escherichia coli in the Viable But Nonculturable State

Abstract

The aim of this study was to analyse the chemical composition of peptidoglycan and the state of some of the enzymes involved in its metabolism in Escherichia coli KN126 in the viable but nonculturable (VBNC) state which is a survival strategy adopted by bacteria (including those of medical interest) when exposed to environmental stresses. When entering the VBNC state, E. coli cells miniaturised and became coccus-shaped. Analysis of peptidoglycan chemical composition, by separation in HPLC of muropeptides released by muramidase digestion of purified peptidoglycan, indicated a high degree of cross-linking, a threefold increase in unusual DAP-DAP cross-linking, an increase in muropeptides bearing covalently bound lipoprotein, and a shortening of the average length of glycan strands in comparison with dividing cells. Analysis of penicillin-binding proteins (PBPs), enzymes involved in the terminal stage of peptidoglycan assembly showed the disappearance of high-molecular-weight PBPs 1A, 1B, 2, and 3 in VBNC cells. Finally, VBNC cells displayed an autolytic capability which was far higher than that of exponentially growing cells. It is suggested that part of these alterations of peptidoglycan may be connected with the VBNC state.

Characterization of the dapA - nlpB Genetic Locus Involved in Regulation of Swarming Motility, Cell Envelope Architecture, Hemolysin Production, and Cell Attachment Ability in Serratia marcescens

“…After removal of the signal sequence, N-acyltransferase acylates the ␣ amino group of the cysteine with a long-chain fatty acid to yield the mature lipoprotein (15,32). In E. coli, the N terminus of a major membrane lipoprotein, Lpp, has been shown to be situated in the outer membrane, with its C terminus linked to DAP (39). In conjunction with this and other studies of E. coli NlpB Ec , we speculated that NlpB Sm might also be connected to the outer membrane through its N terminus, with its C-terminal domain extended to peptidoglycan through a direct linkage to DAP.…”

Bacterial Growth and Cell Division: a Mycobacterial Perspective

“…E. coli, which can also enter a state of nonreplication, has been shown to rapidly modify its PG, making it more highly cross-linked with DAP-DAP bonds and less hydrolyzable by enzymes that typically break it down (158,320,(413)(414)(415). Similarly, Enterococcus faecalis nonreplicating cells are twice as resistant to mechanical disruption as vegetative or stationary-phase cells and have a higher percentage of crosslinked PG (383), with more DAP-DAP cross-links and shortened glycan strands (382), and are O acetylated, which inhibits chicken egg white lysozyme (212). Considering the changes seen in the mycobacterial cell wall, as well as in the PGs of other bacteria when grown under hypoxic conditions, it may be that Rpf is required to degrade specific types of PG that arise under specific nutrient-limiting conditions.…”

Peptidoglycan Hydrolases of Escherichia coli

“…Some kind of triggering is necessary to promote the breakdown of the barrier and the attack of PG by the autolysins (90). This is brought about by submitting harvested cells to osmotic shocks or by treating them with highsalt concentrations, sucrose, trichloroacetic acid (TCA), EGTA, EDTA, or chaotropic agents (90,108,139,239). These treatments disorganize the cell envelope and lead to high rates of extensive cell lysis, with over 60 to 80% PG breakdown, as visualized by the disappearance of the PG material over the whole cell surface (141).…”