Survival in seawater of Escherichia coli cells grown in marine sediments containing glycine betaine

Considering both the protective effect of glycine betaine (GB) on enteric bacteria grown at high osmolarity and the possible presence of GB in marine sediments, we have analyzed the survival, in nutrient-free seawater, of Escherichia coli cells incubated in sediments supplemented with GB or not supplemented and measured the efficiency of GB uptake systems and the expression of proP and proU genes in both seawater and sediments. We did this by using strains harboring proP-lacZ and proU-lacZ operon or gene fusions. We found that the uptake of GB and the expression of both proP and proU were very weak in seawater. The survival ability of cells in seawater supplemented with GB was a linear function of GB concentration, although the overall protection by the osmolyte was low. In sediments, proP expression was weak and GB uptake and proU expression were variable, possibly depending on the availability of organic nutrients. In a sediment with a high total organic carbon content, GB uptake was very high and proU expression was enhanced; cells previously incubated in this sediment showed a higher resistance to decay in seawater. GB might therefore play a significant role in the long-term maintenance of enteric bacterial cells in some marine sediments.