Ecological Aspects of Enzymatic Activity in Marine Sediments

The supply of organic material is a key factor determining the structure and activity of benthic microbial communities. The overwhelming portion of the organic matter entering the sediment via sedimentation is particulate organic carbon, which has to be extracellularly decomposed by enzymes prior to incorporation into microbial cells. The enzymatic hydrolysis of higher-molecular-weight material is considered to be the rate-limiting step in the process of organic matter oxidation in sediments (Billen, 1982; Meyer-Reil, 1987b). The decomposition processes are controlled by microbial (exclusively bacterial?) enzymes which degrade polymeric compounds extracellularly, and their oligomeric products become available substrates for uptake by microbial cells. If the hydrolysis products are not taken up directly, they are fed into the pool of dissolved substrates in sediments. Through microbial attack on particles, refractory organic carbon becomes more easily assimilable for higher trophic levels (Meyer-Reil, 1983).