THE LOSS OF CULTURABILITY BY ESCHERICHIA-COLI-CELLS IN SEAWATER DEPENDS ON AVAILABILITY OF PHOSPHATE IONS AND PHOSPHATE-TRANSPORT SYSTEMS

Using strains with or without the PhoE porin or different components o f the phosphate regulon, we determined that maintenance of the cultura bility of Escherichia coli in seawater depended significantly on the p resence of structures allowing access of phosphate ions to the peripla sm, then to the cytoplasm of cells. Cells totally deprived of the two main phosphate transport systems (Pit, Pst) exhibited the highest loss of culturability. Most of this effect resulted from the loss of the h igh-affinity Pst system, and more specifically that of the periplasmic phosphate-binding protein PhoS. Survival was enhanced in seawater sup plemented with phosphate (0.5 mM), whether or not these structures wer e present. From an ecological point of view, it is assumed that the pr esence of phosphate ions, even at low concentrations, can influence th e behavior of E. coli cells in seawater.