Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not

Stress, including that caused by ethanol, has been shown to induce or promo te secondary metabolism in a number of microbial systems. Rotating-wall bio reactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether t he poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. W e found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, ad dition of various concentrations of ethanol to such bioreactors (or to shak en flasks) failed to increase microcin B17 production. Ethanol stress merel y decreased production and, at higher concentrations, inhibited growth. Int erestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.