Patterns of extracellular enzyme activities among pelagic marine microbial communities: implications for cycling of dissolved organic carbon

The potential for pelagic microbial communities to hydrolyze high molecular weight substrates and therefore to initiate remineralization of high-molecular-weight dissolved organic carbon (DOC) was assessed at 8 different stations spanning a range of locations. Six structurally diverse polysaccharides were used to investigate activities and structural specificities of a related class of microbial extracellular enzymes, the polysaccharide hydrolases. Three high-latitude (57 to 79degreesN) stations showed similar rates and patterns of enzyme activity, with only 3 of 6 polysaccharides hydrolyzed. Hydrolysis at the other stations (39degreesS to 29degreesN) showed a variety of patterns, in which 2 to 5 of the polysaccharides were hydrolyzed. One of the polysaccharides, fucoidan, was not hydrolyzed at any station, while only laminarin was hydrolyzed at every station. A limited ability of microbial communities in some locations to hydrolyze high-molecular-weight substrates could help explain the persistence of a fraction of DOC in the ocean, Potential hydrolysis rates showed no correlation with factors such as environmental temperature or total cell numbers. Denaturing gradient gel electrophoresis analysis of community 16S rDNA indicated that the microbial communities at these locations were diverse, consistent with the diversity in patterns of enzyme activities.