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Journal of Bacteriology, August 2002, p. 4233-4239, Vol. 184, No. 15
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.15.4233-4239.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Role of the Murein Precursor UDP-N-Acetylmuramyl-L-Ala--D-Glu- meso-Diaminopimelic Acid-D-Ala-D-Ala in Repression of ß-Lactamase Induction in Cell Division Mutants

Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111

Received 20 March 2002/ Accepted 6 May 2002

Certain ß-lactam antibiotics induce the chromosomal ampC ß-lactamase of many gram-negative bacteria. The natural inducer, though not yet unequivocally identified, is a cell wall breakdown product which enters the cell via the AmpG permease component of the murein recycling pathway. Surprisingly, it has been reported that ß-lactamase is not induced by cefoxitin in the absence of FtsZ, which is required for cell division, or in the absence of penicillin-binding protein 2 (PBP2), which is required for cell elongation. Since these results remain unexplained, we examined an ftsZ mutant and other cell division mutants (ftsA, ftsQ, and ftsI) and a PBP2 mutant for induction of ß-lactamase. In all mutants, ß-lactamase was not induced by cefoxitin, which confirms the initial reports. The murein precursor, UDP-N-acetylmuramyl-L-Ala--D-Glu-meso-diaminopimelic acid-D-Ala-D-Ala (UDP-MurNAc-pentapeptide), has been shown to serve as a corepressor with AmpR to repress ß-lactamase expression in vitro. Our results suggest that ß-lactamase is not induced because the fts mutants contain a greatly increased amount of corepressor which the inducer cannot displace. In the PBP2(Ts) mutant, in addition to accumulation of corepressor, cell wall turnover and recycling were greatly reduced so that little or no inducer was available. Hence, in both cases, a high ratio of repressor to inducer presumably prevents induction.

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