Affiliation:
1. Fachbereich Biologie, Molecular Microbiology,
2. Fachbereich Chemie, Bioorganic and Organic Chemistry, University of Constance, 78457 Constance, Germany
Abstract
ABSTRACT
We identified a pathway in
Bacillus subtilis
that is used for recovery of
N
-acetylglucosamine (GlcNAc)-
N
-acetylmuramic acid (MurNAc) peptides (muropeptides) derived from the peptidoglycan of the cell wall. This pathway is encoded by a cluster of six genes, the first three of which are orthologs of
Escherichia coli
genes involved in
N
-acetylmuramic acid dissimilation and encode a MurNAc-6-phosphate etherase (MurQ), a MurNAc-6-phosphate-specific transcriptional regulator (MurR), and a MurNAc-specific phosphotransferase system (MurP). Here we characterized two other genes of this cluster. The first gene was shown to encode a cell wall-associated β-
N
-acetylglucosaminidase (NagZ, formerly YbbD) that cleaves the terminal nonreducing
N
-acetylglucosamine of muropeptides and also accepts chromogenic or fluorogenic β-
N
-acetylglucosaminides. The second gene was shown to encode an amidase (AmiE, formerly YbbE) that hydrolyzes the
N
-acetylmuramyl-
l
-Ala bond of MurNAc peptides but not this bond of muropeptides. Hence, AmiE requires NagZ, and in conjunction these enzymes liberate MurNAc by sequential hydrolysis of muropeptides. NagZ expression was induced at late exponential phase, and it was 6-fold higher in stationary phase. NagZ is noncovalently associated with lysozyme-degradable particulate material and can be released from it with salt. A
nagZ
mutant accumulates muropeptides in the spent medium and displays a lytic phenotype in late stationary phase. The evidence for a muropeptide catabolic pathway presented here is the first evidence for cell wall recovery in a Gram-positive organism, and this pathway is distinct from the cell wall recycling pathway of
E. coli
and other Gram-negative bacteria.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology