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

The influence of the quality of organic matter on the hydrolysis of polymers by marine bacteria was investigated in microcosms containing aggregates created in rolling tanks. Two types of microcosms were analysed: microcosms type M1 from unaltered seawater and microcosms type M2 from phytoplankton cultures. Kinetics of aminopeptidase, �-glucosidase and �-glucosidase were measured in the ambient water and the aggregates in the two types of microcosms. Bacteria attached to aggregates expressed enzymes with Km values higher than those of the bacteria in the ambient water for the three hydrolytic activities analysed in both types of microcosms. Attached bacteria showed higher rates of polymer hydrolysis than free-living bacteria only in microcosms M2 created from freshly produced phytoplanktonic material, while free-living bacteria were more active than attached bacteria in the microcosms M1 containing unaltered seawater. The ratio Vmax/Km, which describes the ability of enzymes to compete at low substrate concentration, shows that free-living bacteria are more efficient at dealing with low substrate concentrations in microcosms derived from natural seawater, where the liquid phase 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 attached and free-living bacteria are significantly influenced by the quality of the aggregates and the consequences of this influence are discussed.