Ethanol tolerance in Escherichia coli DH5-Alpha developed by serial exposure to sublethal doses is conferred to wild strains by horizontal gene transfer

Abstract

Microorganisms evolve novel mechanisms and pathways to mitigate various stresses. These are developed by the accumulation of beneficial mutations over many generations. Such adaptations are often transferred from mutant microorganisms that develop it intrinsically to wild ones through horizontal gene transfer (HGT). It allows the latter to acquire favourable traits without having to employ resources to natively evolve. We ascertained this in Escherichia coli by first developing tolerance to ethanol, a potent disinfectant, by laboratory evolution and then transmitting it to the wild strain by HGT. Naturally, wild type E. coli cannot survive beyond 35% v/v ethanol in LB media. By serially increasing the concentration of ethanol by 5% v/v and selecting the surviving colonies, we were able to impose an artificial selection pressure. This in vitro microevolution increased the ethanol tolerance in our mutant to 75% v/v. To test if this tolerance could be transferred to the wild strain through HGT, we meticulously exposed the ancestral wild E. coli to the newly tolerant mutants to facilitate the exchange of genetic material. After our exposure, the unadapted wild type E. coli acquired tolerance up to 55% v/v through transformation and 45% v/v through transduction. The baseline tolerance of 35% v/v remained unchanged after conjugation. While our results are still preliminary, they provide interesting insights into the role horizontal gene transfer in developing resistance to bacteriocidal stressors.