BACTERIAL ECTOENZYMES IN MARINE WATERS - ACTIVITY RATIOS AND TEMPERATURE RESPONSES IN 3 OCEANOGRAPHIC PROVINCES

Ectoenzymatic hydrolysis is a crucial first step in bacterial utilizat ion of polymeric dissolved organic matter (DOM), Variation in the rela tive activities of different enzymes can indicate seasonal and geograp hic variation in the mode of bacterioplankton nutrition. We found that relative activities of leucine aminopeptidase and beta-glucosidase in seawater varied significantly among three oceanic regions: the subtro pical North Pacific, the equatorial Pacific, and the Southern Ocean. T he temperature responses of these enzymes also vary significantly amon g these three regions, suggesting distinct bacterial phenotypes with d istinct isozymes, Our results suggest a latitudinal trend in bacterial carbon and nitrogen utilization, with significant synthesis of cell c onstituents from glucose and ammonium in equatorial waters but little such de novo synthesis in Antarctic waters. The observed patterns have important implications for the parameterization of secondary producti on and nutrient regeneration in global production models and for under standing the role of DOM in global carbon and nitrogen fluxes.