EFFECT OF SIMULATED MICROGRAVITY AND SHEAR-STRESS ON MICROCIN B17 PRODUCTION BY ESCHERICHIA-COLI AND ON ITS EXCRETION INTO THE MEDIUM

Production of the antibacterial polypeptide microcin B17 (MccB17) by E scherichia coli ZK650 was inhibited by simulated microgravity. The sit e of MccB17 accumulation was found to be different, depending on wheth er the organism was grown in shaking Basks or in rotating bioreactors designed to establish a simulated microgravity environment, In flasks, the accumulation was cellular, but in the reactors, virtually all the microcin was found in the medium, The change from a cellular site to an extracellular one was apparently not a function of gravity, since e xtracellular production occurred in these bioreactors, irrespective of whether they were operated in the simulated microgravity or normal gr avity mode, More probably, excretion is due to the much lower degree o f shear stress in the bioreactors, Addition of even a single glass bea d to the 50-ml medium volume in the bioreactor created enough shear to change the site of MccB17 accumulation from the medium to the cells.