TITLE:    Bacterial ectoenzymes in marine waters: activity ratios and
          temperature responses in three oceanographic provinces
        
AUTHOR:   James R Christian and David M Karl

JOURNAL:  Limnology and Oceanography 

DATE:     1995


ABSTRACT: 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.  In
this study, 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 the role of
DOM in global carbon and nitrogen fluxes.