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J. Bacteriol. doi:10.1128/JB.00415-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Role of peptidoglycan amidases in the development and morphology of the division septum in Escherichia coli

Department of Microbiology and Immunology, University of North Dakota School of Medicine, Grand Forks, North Dakota, USA, 58202-9037; Centro de Biología Molecular ‘Severo Ochoa’ Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Facultad de Ciencias, Madrid, Spain

^* To whom correspondence should be addressed. Email: kyoung{at}medicine.nodak.edu.

	Abstract

Escherichia coli contains multiple peptidoglycan-specific hydrolases but their physiological purposes are poorly understood. Several mutants lacking combinations of hydrolases grow as chains of unseparated cells, indicating that these enzymes help cleave the septum to separate daughter cells after cell division. Here we confirm previous observations that in the absence of two or more amidases thickened and dark bands, which we term septal peptidoglycan rings (SP-rings), appear at division sites in isolated sacculi. The formation of SP-rings depended on active cell division, and they apparently represent a cell division structure that accumulates because septal synthesis and hydrolysis are uncoupled. Even though septal constriction was incomplete, SP-rings exhibited two properties of mature cell poles: they behaved as though composed of inert peptidoglycan and they attracted the IcsA protein. Despite not being separated by a completed peptidoglycan wall, adjacent cells in these chains were often compartmentalized by the inner membrane, indicating that cytokinesis could occur in the absence of invagination of the entire cell envelope. Finally, deletion of PBP 5 from amidase mutants exacerbated the formation of twisted chains, producing numerous cells having septa with abnormal placements and geometries. The results suggest that the amidases are necessary for continued peptidoglycan synthesis during cell division, that their activities help create a septum having the appropriate geometry, and that they may contribute to the development of inert peptidoglycan.

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