Use of perfused cores for evaluating extracellular enzyme activity in stream-bed sediments

Abstract

β-Glucosidase activity was investigated in stream-bed sediments using 4-methylumbelliferyl-β-d-glucopyranoside (MUF-β-Glc) as a model substrate. In a perfused core technique, water containing MUF-β-Glc was perfused up through sediment cores. β-glucosidase activity quantified from the release of fluorescent MUF in water discharge from the cores. At low rates of perfusion, maximum β-glucosidase activity (Vmax) in perfused sediments was similar to that in suspended (unperfused) sediments. Substrate affinity(Km)was higher in the suspended sediments.VmaxandKmboth increased when the perfusion rate was raised, although naturally-low substrate concentrations could mean that variability in perfusion rates has little effect on enzyme activity in the field. Vmax was uninfluenced by whether ground or stream water was perfused through the sediments, but Km was higher in cores perfused with groundwater. Increasing concentrations of glucose in the perfusion water resulted in a progressive inhibition of β-glucosidase activity. Although natural concentrations of glucose were low, the high turnover of enzymatically-released glucose probably means that β-glucosidase activity could be regulated by product concentration.