Study of the decomposition of organic polymers in Mediterranean basins through the measurements of microbial enzymatic activities.

Knowledge of the processes involved in the turnover of organic matter is of utmost importance to understand ecosystem functioning. In most of the aquatic ecosystems, microorganisms are major players in the cycling of biogeochemical nutrients (Nitrogen, Phosphorus) and Carbon through their enzymatic activities (leucine aminopeptidase, alkaline phosphatase and beta-glucosidase) on organic polymers (proteins, organic phosphates and polysaccharides, respectively). The small monomers released by decomposition may be used by microbes themselves for their growth. Estimates of the decomposition rates of organic polymers are performed using fluorogenic compounds, analogues to natural substrates, whose hydrolysis rate allow us to obtain information on the potential metabolic activity of the prokaryotic community. This note refers some of the results obtained during recent oceanographic cruises performed in the Tyrrhenian and Ionian Seas, with the aim of evaluating the contribution of the prokaryotic community to organic matter decomposition and the changes in microbial activity patterns during different seasonal conditions. Enzyme measurements revealed significant variations in the rates of hydrolytic activities in relation to space and time, with the highest levels generally found during summer and in upper epipelagic layer; sporadic peaks (hot spots) of enzyme activity are also detected in meso- and bathypelagic layers, due to the presence of different water masses.