Protective Effect of Glycine Betaine on Survival of Escherichia coli Cells in Marine Environments

Abstract

Under marine conditions, Escherichia coli cells develop extensive structural, metabolic and (to some extent) genetic changes which can be considered as adaptive processes rather than the expression of an irreversible decay. Such adaptation strongly depends on the previous history of growth of the cells and on whether they can regulate internal osmotic pressure when entering the sea. All known osmoregulation mechanisms can help the cells to survive at high osmolarity, but their efficiency depends both on expression of genes responsible for osmoregulation and normal functioning of osmoregulatory mechanisms under marine conditions. The paper presents some experimental evidence on the influence of osmoregulation processes on the survival of E. coli cells in seawater and sediments. This was investigated using strains harboring proP- and proll-lacZ gene or operon fusions. It is shown that the uptake of glycine betaine (GB) and the expression of both proP and proU were weak in seawater. In marine sediments, proP expression was weak, and GB uptake and proU expression were variable, probably depending on the availability of nutrients. In sediment with a high total organic carbon content, GB uptake was very high and proU expression enhanced; cells previously incubated in this sediment showed a higher resistance to decay in seawater. These results confirm that marine deposits can act as reservoirs for enteric pathogens and may give rise to resistant cells.