Polysaccharide degradation and utilisation during a spring phytoplankton bloom in the northwestern Adriatic Sea

The northern Adriatic Sea is among the most productive areas within the Mediterranean Sea, mainly because of the important river discharges that characterise the area. During an oceanographic cruise in April 2011, 12 stations located in the western sector of the basin were sampled in order to deepen the current knowledge on polysaccharide utilisation within phytoplankton blooms. The bloom detected in the proximity of the Po river delta was mainly supported by Skeletonema marinoi and several species of Chaetoceros and determined the spatial distribution of total carbohydrates in surface and subsurface waters. The kinetics of four glycolytic exoenzymes were tested (alpha- and beta-glucosidase together with alpha- and beta-galactosidase), and cellulose-degrading and cellobiose-utilising microbes were enumerated. The fastest enzymatic cleavage was performed by alpha-galactosidase in low-chlorophyll areas. The highest abundance of cellulose-degrading microorganisms corresponded to the lowest degradation rates. Relatively slow hydrolysis was compensated by a pronounced affinity of the enzymes for their substrates. This metabolic strategy would minimise energy consumption, by producing few, high-performance enzymes. No evident relationship between phytoplankton assemblages and polysaccharide degradation dynamics was found.