Complementation of growth defect in an ampC deletion mutant of Escherichia coli

Abstract β-Lactamase genes of class-A ( Rtem ) and class-C ( ampC ) were placed under control of an inducible tac -promoter and expressed in Escherichia coli . Expression of RTEM had no observable effect on the growth properties of E. coli strains HB101 ( ampC ⁺) or MI1443 (Δ ampC ). E. coli MI1443 exhibited a decline in growth rate at mid-exponential phase which could be delayed by expression of AmpC at early-exponential phase. AmpC expression otherwise inhibited growth, particularly during the transition into exponential phase where growth was prevented altogether. We suggest that the AmpC β-lactamase, but not RTEM, may have an additional cellular function as a peptidoglycan hydrolase.