AmpG is required for Bla_Xc beta-lactamase expression in Xanthomonas campestris pv. campestris str. 17

The chromosomal ampR_Xc-bla_Xc module is essential for the β-lactam resistance of Xanthomonas campestris pv. campestris. Bla_Xc β-lactamase is expressed at a high basal level in the absence of an inducer and its expression can be further induced by β-lactam. In enterobacteria, ampG encodes an inner membrane facilitator involved in the recycling of murein degradation compounds. An isogenic ampG mutant (XcampG) of X. campestris pv. campestris str. 17 (Xc17) was constructed to investigate the link between murein recycling and bla_Xc expression. Our data demonstrate that (1) XcampG is susceptible to β-lactam antibiotics; (2) AmpG_Xc is essential for expression of bla_Xc; (3) AmpGs of Xc17, Stenotrophomonas maltophilia KJ (SmKJ) and Escherichia coli DH5α can complement the defect of XcampG; (4) overexpression of AmpG_Xc significantly increased bla_Xc expression; and (5) AmpG_Xc from Xc17 is able to restore β-lactamase induction of the ampN_Xc-ampG_Xc double mutant of SmKJ. In Xc17, ampG_Xc can be expressed from the promoter residing in the intergenic region of ampN_Xc-ampG_Xc and the expression is independent of β-lactam induction. AmpN, which is required for β-lactamases induction in SmKJ, is not required for the β-lactam antibiotic resistance of Xc17.