Role of the phosphatase PhoX in the phosphorus metabolism of the marine bacterium Ruegeria pomeroyi DSS-3.

Marine microbes are adapted to surviving in a variable phosphorus (P) environment. This adaptation frequently involves the presence of periplasmic or cell membrane-associated enzymes that enable them access to alternative sources of P when phosphate is depleted. In a recent study we identified the phosphatase PhoX as an enzyme that may be essential in mediating organic P acquisition in the ocean. Here we have investigated the role of this enzyme in the utilization of different P sources, using as a model the marine bacterium Ruegeria pomeroyi DSS-3. Although our previous study had demonstrated that PhoX accounts for more than 90% of the alkaline phosphatase (APase) activity in R. pomeroyi, a PhoX mutant strain was able to grow on monophosphate esters at the same rate as the wild type. Nevertheless, further APase kinetic analyses with both strains demonstrated that the Km of the wild-type strain was an order of magnitude lower than the mutant strain, indicating that PhoX is crucial for the use of these substrates at low concentrations, typically found in seawater. We also showed that PhoX is required for efficient hydrolysation of nucleotides like ADP and ATP.