COMPLEMENTATION OF GROWTH DEFECT IN AN AMPC DELETION MUTANT OF ESCHERICHIA-COLI

beta-Lactamase genes of class-A (Rtem) and class-C (ampC) were placed under control of an inducible tac-promoter and expressed in Escherichi a coli. Expression of RTEM had no observable effect on the growth prop erties of E. coli strains HB101 (ampC(+)) or MI1443 (Delta ampC). E. c oli MI1443 exhibited a decline in growth rate at mid-exponential phase which could be delayed by expression of AmpC at early-exponential pha se. AmpC expression otherwise inhibited growth, particularly during th e transition into exponential phase where growth was prevented altoget her. We suggest that the AmpC beta-lactamase, but not RTEM, may have a n additional cellular function as a peptidoglycan hydrolase.