Genetic typing of Pseudomonas aeruginosa isolated from the open ocean has revealed that marine strains form unique clusters. To clarify whether this genetic variation reflects differences in pattern of culturability and survival, a marine strain was compared with a freshwater strain and a clinical strain in microcosms with different levels of NaCl (0 to 7% [w/v]), pH (4.0 to 9.0) and temperature (-20, 0, 4, 25 and 37°C) in both artificial seawater (ASW) and distilled water (DW). The viable but non-culturable (VBNC) state of P. aeruginosa was also monitored. The marine strain 1200 grew better at high NaCl and pH, whereas the freshwater strain 1030 did better at 0 to 3% NaCl and a pH of less than 7.0. The clinical strain 1564 grew best at neutral pH and 0% NaCl. No significant differences were observed among the strains in culturability at different temperatures. Like other bacteria, P. aeruginosa enters a VBNC state under stressful conditions. The marine P. aeruginosa isolate exhibits a unique pattern of culturability and survival which demonstrates a physiological adaptation to the ocean environment.