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Journal of Bacteriology, August 2009, p. 5094-5107, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00505-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

LytM-Domain Factors Are Required for Daughter Cell Separation and Rapid Ampicillin-Induced Lysis in Escherichia coli{triangledown}

Tsuyoshi Uehara,{dagger} Thuy Dinh,{dagger} and Thomas G. Bernhardt*

Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, Massachusetts 02115

Received 12 April 2009/ Accepted 3 June 2009

Bacterial cytokinesis is coupled to the localized synthesis of new peptidoglycan (PG) at the division site. This newly generated septal PG is initially shared by the daughter cells. In Escherichia coli and other gram-negative bacteria, it is split shortly after it is made to promote daughter cell separation and allow outer membrane constriction to closely follow that of the inner membrane. We have discovered that the LytM (lysostaphin)-domain containing factors of E. coli (EnvC, NlpD, YgeR, and YebA) are absolutely required for septal PG splitting and daughter cell separation. Mutants lacking all LytM factors form long cell chains with septa containing a layer of unsplit PG. Consistent with these factors playing a direct role in septal PG splitting, both EnvC-mCherry and NlpD-mCherry fusions were found to be specifically recruited to the division site. We also uncovered a role for the LytM-domain factors in the process of β-lactam-induced cell lysis. Compared to wild-type cells, mutants lacking LytM-domain factors were delayed in the onset of cell lysis after treatment with ampicillin. Moreover, rather than lysing from midcell lesions like wild-type cells, LytM– cells appeared to lyse through a gradual loss of cell shape and integrity. Overall, the phenotypes of mutants lacking LytM-domain factors bear a striking resemblance to those of mutants defective for the N-acetylmuramyl-L-alanine amidases: AmiA, AmiB, and AmiC. E. coli thus appears to rely on two distinct sets of putative PG hydrolases to promote proper cell division.

* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, Harvard Medical School, Armenise Building, Rm. 302A, 200 Longwood Ave., Boston, MA 02115. Phone: (617) 432-6971. Fax: (617) 738-7664. E-mail: thomas_bernhardt{at}hms.harvard.edu

{triangledown} Published ahead of print on 12 June 2009.

{dagger} T.U. and T.D. contributed equally to this study.

Journal of Bacteriology, August 2009, p. 5094-5107, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00505-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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