Influence of hypoxia on bacteremia in the Dungeness crab, Cancer magister.

We examined the possibility that decreased environmental oxygen can elevate the levels of indigenous bacteria in the hemolymph of Cancer magister. Crabs were exposed to air-saturated and hypoxic (50% air-saturation) water for 3 days and levels of culturable bacteria in hemolymph were measured every 24 h as the total number of colony-forming units (CFU) per milliliter of hemolymph. Bacteremia increased after 24 h of exposure to hypoxia and persisted for 72 h, whereas crabs exposed to normoxia had no measurable change in number of culturable bacteria. The predominant persistent bacteria in the hemolymph was isolated and identified by DNA sequence-based methods as Psychrobacter cibarus. Crabs were injected with P. cibarus or with buffered saline as a control after 3 h of hypoxia. Levels of culturable bacteria were significantly higher in hypoxic crabs than in normoxic ones (about 2500 versus 1000 CFU ml(-1) 80 min post-injection, respectively), and circulating levels of oxygen were significantly reduced in infected animals compared to uninfected ones after 48 h in hypoxia and after 72 h in air-saturated water post-injection. These data demonstrate that P. cibarius is present in Dungeness crabs, that environmental hypoxia can dramatically elevate levels of persistent bacteria, and that hypoxia in the presence of hemolymph bacteria may ultimately reduce immune and respiratory ability.