Successive changes in bacterioplankton communities in the river rhine after copper additions

Abstract

The sensitivity of bacterioplankton to copper was analyzed to see whether initial steps in the selection of copper‐tolerant life‐forms in mixed populations of bacteria were accompanied by changes in basic metabolic parameters. Analysis took place by measuring the incorporation of [3H]thymidine and [3H]leucine, and the hydrolysis of leucyl‐β‐naphthylamide over a period of 4 d. In acute toxicity tests the radiochemically determined parameters showed the same sensitivities to copper, whereas in the enzyme test the dose‐response curve had a much lower slope, indicating less sensitivity. Marked differences were observed in the susceptibility of the different processes after prolonged exposure to copper. Incorporation of [3H]thymidine, [3H]leucine, and proteolytic activity changed substantially during exposure to concentrations as low as 2 to 31 μg Cu L−1. Higher copper concentrations (126‐1,000 μg Cu L−1) led in the course of 24 to 48 h to the development of a bacterial community with a higher overall copper tolerance. In winter, these successive events in bacterial populations were observed in the absence of substantial populations of algae or zooplankton. In summer, the metabolic changes in bacterioplankton exposed to copper were strongly affected by the poisoning of other organisms, notably algae, and the subsequent release of organic material. Thus, moderate copper concentrations alter the metabolic profile of bacterial communities, probably as an initial step in the selection of tolerant life‐forms.

Analysis of Structural and Physiological Profiles To Assess the Effects of Cu on Biofilm Microbial Communities

“…These authors did not detect large differences between bacterial communities growing at Cu concentrations ranging from 3 to 87 M. Our results suggest that the complex and organized structure of the biofilm (10,18,30) would not protect the bacterial community in the same way that sediments do, even through the formation of extracellular polymeric substances was found to increase several resistance capacities of each encased organism (24) by reducing the bioavailability of heavy metals (33). Short-and long-term toxicity tests of heavy metals on aquatic biofilms have focused either on the response of the phototrophic compartment (1,2,5,17) or on that of the heterotrophic compartment (34), but toxic effect assessments based on physiological tests (3,19) or studies considering the biofilm as a whole have not investigated the effect of Cu (6,23). Possible interactions between phototrophic and heterotrophic compartments of a biofilm may be disturbed when one compartment is severely affected by a stress factor, e.g., an increase in toxicant concentration.…”