Responses of enteric bacteria to environmental stresses in seawater

The effects of different environmental factors (nutrient deprivation, hyper osmotic shock, exposure to light) on enteric bacteria which have been trans ferred into the marine environment, have been studied experimentally (micro cosms) by considering demographic, physiological and genetic responses in E scherichia coli or Salmonella typhimurium populations. Short-term experimen ts (less than or equal to 48 h) showed that nutrient deprivation induced li mited changes in measured bacteriological variables, but when combined with hyperosmotic shock, it results in an energy charge decrease and inactivati on of membrane transport. Light exposure mainly affects the colony-forming capacity of bacterial populations. Combining different stress factors confi rmed the rapid appearance of a viable, but nonculturable state (VBNC) in po pulations of E. coli and S. typhimurium. It has been shown that cellular fo rms other than those previously described in the literature can be generate d following incubation in seawater. It was also established that pre-adapta tion phenomena may occur, leading to better survival (e.g. pre-incubation i n seawater in darkness enhanced survival under light exposure). An explanat ion concerning these phenomena can be found by looking at the rpoS gene whi ch controls the expression of numerous genes and can trigger a general anti -stress response under different adverse conditions. Although the results p rovide better comprehension of the fate of enteric bacteria in the marine e nvironment, they also raise numerous questions related to fundamental and a pplied problems, given in the conclusion of this paper. (C) Elsevier, Paris .