Influence of organic matter quality in the cleavage of polymers by marine bacterial communities

The influence of the quality of organic matter on the hydrolysisof polymers by marine bacteria was investigated in microcosmscontaining aggregates created in rolling tanks. Two types ofmicrocosms were analysed: microcosms type M1 from unalteredseawater and microcosms type M2 from phytoplankton cultures.Kinetics of aminopeptidase, -glucosidase and ß-glucosidasewere measured in the ambient water and the aggregates in thetwo types of microcosms. Bacteria attached to aggregates expressedenzymes with K_m values higher than those of the bacteria inthe ambient water for the three hydrolytic activities analysedin both types of microcosms. Attached bacteria showed higherrates of polymer hydrolysis than free-living bacteria only inmicrocosms M2 created from freshly produced phytoplanktonicmaterial, while free-living bacteria were more active than attachedbacteria in the microcosms M1 containing unaltered seawater.The ratio V_max/K_m, which describes the ability of enzymes tocompete at low substrate concentration, shows that free-livingbacteria are more efficient at dealing with low substrate concentrationsin microcosms derived from natural seawater, where the liquidphase may be depleted of utilizable dissolved organic matter,than in the microcosms derived from phytoplankton cultures.Our data suggest that the hydrolytic activities of both attachedand free-living bacteria are significantly influenced by thequality of the aggregates and the consequences of this influenceare discussed.