LIMNOLOGY AND OCEANOGRAPHY, 40, 1042-1049

Bacterial ectoenzymes in marine waters: Activity ratios and temperature responses in three oceanographic provinces

James R. Christian and David M. Karl

School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu 96822

Ectoenzymatic hydrolysis is a crucial first step in bacterial utilization of polymeric dissolved organic matter (DOM). Variation in the relative activities of different enzymes can indicate seasonal and geographic 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 subtropical North Pacific, the equatorial Pacific, and the Southern Ocean. The temperature responses of these enzymes also vary significantly among these three regions, suggesting distinct bacterial phenotypes with distinct isozymes. Our results suggest a latitudinal trend in bacterial carbon and nitrogen utilization, with significant synthesis of cell constituents 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 production and nutrient regeneration in global production models and for understanding the role of DOM in global carbon and nitrogen fluxes.