Bacterial decomposition of marine aggregates and its biogeochemical significance

Bacteria play an integral role in shaping the ocean's biogeochemistry. It is now generally agreed that bacteria constitute a large, active component of the ocean's biology and that a significant fraction of the organic carbon produced in the ocean is utilized to support their growth. Since bacteria are restricted to the uptake of small molecules, it follows that much of the organic carbon flux is through the dissolved pool. How organic carbon enters this pool is the subject of much of the research presented here. Specifically, the role of bacterial hydrolytic ectoenzymes in mediating the phase transition of organic matter from particulate to dissolved is examined and the consequences are discussed.;Marine snow aggregates were shown to harbor high levels of hydrolytic ectoenzyme activities, up to three orders of magnitude higher than in the bulk sea water. The hydrolysis rates were in excess of the uptake rates of bacteria resulting in most the hydrolysis products entering the dissolved organic carbon pool. Not all enzymes assayed were enriched to the same degree. Protease and phosphatase occurred at much higher levels than ;The role of bacterial hydrolytic ectoenzymes in carbon fluxes during a phytoplankton bloom was examined in a mesocosm. Despite the absence of metazoan grazers (which are thought to be critical in making organic matter available to bacteria through their feeding activities), 40-65% of the organic carbon produced during the bloom was utilized by the bacteria. This was apparently due to the high levels of hydrolytic ectoenzymes expressed by the bacteria. It is also suggested that the hydrolytic ectoenzyme activities of bacteria attached to diatoms reduced diatom aggregation thereby prolonging the bloom.;It is concluded that much the shaping of the ocean's biogeochemistry by bacteria is through the expression of hydrolytic ectoenzymes and their role in changing the chemical composition and size spectrum of organic matter in the ocean.