N-ACETYLGLUCOSAMINE DYNAMICS IN FRESH-WATER ENVIRONMENTS - CONCENTRATION OF AMINO-SUGARS, EXTRACELLULAR ENZYME-ACTIVITIES, AND MICROBIAL UPTAKE

As a first approach to the study of the dynamics of amino sugars in fr eshwater environments, we measured microbial uptake of N-acetylglucosa mine and hydrolysis of 4-MUF-N-acetyl-beta-glucosaminide by extracellu lar enzymes in fishponds, reservoirs, backwaters, and lakes. Amino sug ars were present in all localities and comprised up to several percent of both dissolved and particulate organic matter. Processes involving N-acetylglucosamine (extracellular enzymes, microbial uptake) were al so detected in all localities; their potential rates accounted for app roximately 10-100% of the rates of analogical processes involving gluc ose and were correlated with dissolved organic C and with general micr obial activity. Two types of 4-MUF-beta-N-acetylglucosaminidases (high and low affinity) were distinguished kinetically. The activity of the high-affinity enzyme was tightly correlated with variables coupled to bacterial activity. In fishponds, uptake of N-acetylglucosamine by di atoms and cyanobacteria was detected via autoradiography.