BIOLOGICAL AND CHEMICAL ASPECTS OF DIFFERENCES IN SENSITIVITY OF NATURAL-POPULATIONS OF AQUATIC BACTERIAL COMMUNITIES EXPOSED TO COPPER

Bacterial populations from the main stream of the River Rhine and its plume in the North Sea, the lower course of the rivers Meuse and Scheldt, and various stagnant waters in the Netherlands were exposed to additions of copper in order to analyze differences in sensitivity. Growth rate, measured as thymidine incorporation rate, was generally more sensitive to copper(EC50:25-310 mug. L-1) than extracellular phosphatase activity, measured as hydrolysis of methylumbelliferin phosphate (EC50: 179-3000 mug . l-1). The EC50 value for copper-inhibited growth was correlated with the ambient total copper concentration, but such a correlation was not evident for copper-inhibited enzymatic activity. Differences in capacity of the waters to chelate an addition of 1000 mug . L-1 of copper were estimated by measuring the inhibition of Photobacterium phosphoreum in the Microtox test. The growth rate of bacteria in the upper, middle, and lower courses of the Rhine showed an increasing tolerance to copper, concurrent with increased input of copper and increasing concentrations of suspended matter in the river. It is indicated in this study that part of the differences in sensitivity of bacterial communities is caused by the chemical conditions (i.e., by complexation), but biological differences in tolerance to copper, possibly induced by pollution, were also indicated.