Kinetic modulation of bacterial hydrolases by microbial community structure in coastal waters

In this study, we hypothesized that shifts in the kinetic parameters of extracellular hydrolytic enzymes may occur as a consequence of seasonal environmental disturbances and would reflect the level of adaptation of the bacterial community to the organic matter of the ecosystem. We measured the activities of enzymes that play a key role in the bacterial growth (leucine aminopeptidase, β- and α-glucosidases) in surface coastal waters of the Eastern Cantabrian Sea and determined their kinetic parameters by computing kinetic models of distinct complexity. Our results revealed the existence of two clearly distinct enzymatic systems operating at different substrate concentrations: a high-affinity system prevailing at low substrate concentrations and a low-affinity system characteristic of high substrate concentrations. These findings could be the result of distinct functional bacterial assemblages growing concurrently under sharp gradients of high-molecular-weight compounds. We constructed an ecological network based on contemporaneous and time-delayed correlations to explore the associations between the kinetic parameters and the environmental variables. The analysis revealed that the recurring phytoplankton blooms registered throughout the seasonal cycle trigger the wax and wane of those members of the bacterial community able to synthesize and secrete specific enzymes.his work has been supported by projects EFICIENCIA (CTM2006-08023) and CAMBIO (CTM2010-19308), co-financed by Ministry of Science and Innovation of the Spanish Government and European FEDER founds, the Basque Government (Grant to Research Group IT1657-22) and by the UPV/EHU (Grant to Research Group GIU10/17). Naiara Abad was supported by a scholarship from the Basque Government and currently by the grant Margarita Salas from the European Union—NextGenerationEU through the UPV/EHU. Zuriñe Baña and Ainhoa Uranga were financed by scholarships from the UPV/EHU