Biphasic extracellular proteolytic enzyme activity in benthic water and sediment in the northwestern mediterranean Sea

In this study, we used the fact that bacteria are able to cleave a fluorogenic substrate analog (L-leucine-7-amido-4-methylcoumarin) to determine the maximal ectoproteolytic activities (Vm) and affinities (Km) of natural benthic microbial communities by the multiconcentration kinetic method. This investigation was performed during the winter and summer of 1997 with a set of 36 samples of near-bottom water and sediment collected from a coastal area and an offshore area in the western part of the Gulf of Lions. The existence of biphasic microbial ectoproteolysis was statistically confirmed for both the near-bottom water and the sediment, regardless of the spatial and seasonal conditions. Globally, 72.2% of the entire set of bacterial consortia collected at the water-sediment boundary layer showed biphasic microbial kinetics. A specific estimator of the biphasicity indicated that deep benthic bacterial consortia responded better with episodic nutrient supplies than shallower benthic bacterial consortia responded.