A new method for measuring polysaccharide hydrolysis rates in marine environments

A new method was used to measure extracellular enzymatic hydrolysis rates of polysaccharides in anoxic sediments of Kiel Bight, Baltic Sea. Two fluorescently-labeled (FLA-) polysaccharides were synthesized and characterized, and their rates of hydrolysis were measured over a sediment depth range of 13 cm. Hydrolysis of both FLA-laminarin (β(1,3)-linked glucose polysaccharide; MW 6000 daltons) and FLA-pullulan (α(1,6)-linked maltotriose groups; MW 200,000) was rapid. For both substrates, hydrolysis was most rapid in surface sediments, and rates decreased with depth. The difference between surface and deep hydrolysis rates was far greater for FLA-laminarin than for FLA-pullulan, and most likely reflected downcore differences in quantities or activities of enzymes. A simple model was used to calculate a lower boundary on potential hydrolysis rates of the two polysaccharides. For FLA-laminarin, potential hydrolysis rates ranged from 11–129 cuts nmol glu cm−3 hr−1, while rates for FLA-pullulan ranged from 17–75 cuts nmol glu cm−3 hr−1. These rates are considerably more rapid than rates previously reported for hydrolysis of MUF-glucose in Kiel Bight sediments, and confirm that at least some types of polysaccharides are rapidly hydrolyzed in sediments. FLA-polysaccharides are stable, sensitive, and unaffected by background fluorescence from dissolved organic matter. The same method could be used to fluorescently label a wide range of polysaccharides, and investigate the effects of specific structural and environmental parameters on extracellular enzymatic hydrolysis rates.