Evidence for psychrophiles outnumbering psychrotolerant marine bacteria in the springtime coastal Arctic

During a springtime study of pelagic microbial activities in the coastal Alaskan Arctic (Chukchi Sea, June 1998), a selective serial dilution technique was used to estimate the relative abundance of cold-loving (psychrophilic) and cold-tolerant (psychrotolerant or psychrotrophic) pelagic bacteria at four stations representing different stages of an algal bloom. Psychrophiles were numerically dominant, regardless of the organic nutrient concentration of their source waters (51-101 mu mol L-1 total organic carbon; 2-17 mu mol L-1 total organic nitrogen). At all stations, lower temperature incubations generated significantly higher most probable number (MPN) estimates. Further, these psychrophiles were unable to acclimate to 20 degrees C over the course of a 3-month incubation. Our pelagic experiments are the first of their kind reported from the Western Arctic, where surface waters are dominated by the Pacific Ocean inflow, and suggest that psychrophiles can dominate even in waters only recently subjected to perennially cold conditions, independent of nutrient status or bloom condition.