NagZ is required for beta-lactamase expression and full pathogenicity in Xanthomonas campestris pv. campestris str. 17

Xanthomonas campestris pv. campestris expresses a chromosomally encoded class A beta-lactamase Bla(xc). Basal expression and induction of bla(xc) require the transcriptional factor AmpR(xc) and the peptidoglycan-monomers permease AmpG(xc). NagZ is a beta-GlcNAcase which cleaves GlcNAc-anhMurNAc peptides (peptidoglycan-monomers) to generate anhMurNAc-peptides. In many bacteria, anhMurNAc-peptides act as activation ligands for AmpR. Nevertheless, the role of NagZ in beta-lactamase induction differs among species. In this paper, we studied the roles of nagZ(xc) in the regulation of bla(xc) and pathogenicity in X. campestris pv. campestris. Our data showed that cells lacking nagZ(xc) dramatically reduced the basal expression and induction of bla(xc), suggesting that anhMurNAc-peptides, products of NagZ(xc), are required for bla(xc) expression regardless of the presence or absence of inducers. Expression of bla(xc) is regulated via an ampG-nagZ-ampR pathway. Pathogenicity assay demonstrated that an ampG(xc) mutant excited more severe symptoms than the wild-type; on the contrary, the nagZ(xc) mutant became less virulent. To our knowledge, this is the first demonstration of a link between the ampG or nagZ defects and the pathogenicity in a plant pathogen. (C) 2014 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.