Adaptative responses of E. coli to marine environmental stresses: a modelling approach based on viability and dormancy concepts

In an attempt to synthesize conceptual and experimental information on the behaviour of enteric bacteria in seawater, a mathematical model has been developed. This model is based on changes in intracellular metabolisable components depending on physiological responses of the cell when subjected to nutrient starvation, salinity stress and solar radiation. Following a strategy which takes into account short- and mid-term physiological adaptation and reversal processes, the cells can develop in different states: culturable (B₁), viable and definitively nonculturable (B₂), and reversibly dormant (B₃) cells. Model parameters were deduced either from original microcosm experiments, from literature data or calibration procedures. Validation of the model was performed through specific data on the patterns of change in culturable cell abundances when Escherichia coli populations were subjected to separate or simultaneous experimental stresses. It was shown that model simulations fit these data satisfactorily. Simulation results clearly show the effectiveness of the antistress response and the importance of dormancy which confers higher resistance properties. The model also makes it possible to test the effect of the different stresses, and the role of pre-adaptation with regard to the dynamics of the different cellular states.