Regulation of microbial enzymatic degradation of organic matter in deep-sea sediments

The enzymatic response of a natural deep-sea microbial community to input of organic matter was investigated by substrate enrichment experiments. Sediments from the BIOTRANS area at 47"N 20°W in the NE Atlantic (4500 m depth) were supplied with particulate and dissolved organic matter from stenhzed net plankton and incubated under in situ pressure and temperature. Changes in the potential hydrolytic activities of the extracellular enzymes aand P-glucosidase, chitobiase, lipase and aminopeptidase were observed over a 15 d incubation period. Direct microscopic counts and phospholipid concentrations were used as measures of microbial biomass. Induction of enzyme production proportional to the supply of organic matter was found for enzymes degrading structural polysaccharides (P-glucosidase, chitobiase), while aminopeptidase activity was Inhibited and no clear effect was found for enzymes degrading storage compounds (a-glucosidase and lipase). Particulate organic matter induced higher enzyme production than equivalent amounts of dissolved organic matter. Only a slight increase in microbial biomass was observed until the end of the experiment after 15 d indicating that changes in enzyme activity were not due to bacterial growth. The observations give evidence that the production of enzymes in natural mixed microbial communities is directly regulated by the supply of appropriate food.