Impact of Metazooplankton Filter Feeding on Escherichia coli under Variable Environmental Conditions

Abstract

The fecal indicator bacterial species <i>Escherichia coli</i> is an important measure of water quality and a leading cause of impaired surface waters. We investigated the impact of the filter-feeding metazooplankton <i>Daphnia magna</i> on the inactivation of <i>E. coli</i> The <i>E. coli</i> clearance rates of these daphnids were calculated from a series of batch experiments conducted under variable environmental conditions. Batch system experiments of 24 to 48 h in duration were completed to test the impacts of bacterial concentration, organism density, temperature, and water type. The maximum clearance rate for adult <i>D. magna</i> organisms was 2 ml h^-1 organism^-1 Less than 5% of <i>E. coli</i> removed from water by daphnids was recoverable from excretions. Sorption of <i>E. coli</i> on daphnid carapaces was not observed. As a comparison, the clearance rates of the freshwater rotifer <i>Branchionus calyciflorus</i> were also calculated for select conditions. The maximum clearance rate for <i>B. calyciflorus</i> was 6 × 10^-4ml h^-1 organism^-1 This research furthers our understanding of the impacts of metazooplankton predation on <i>E. coli</i> inactivation and the effects of environmental variables on filter feeding. Based on our results, metazooplankton can play an important role in the reduction of <i>E. coli</i> in natural treatment systems under environmentally relevant conditions.<b>IMPORTANCE</b><i>Escherichia coli</i> is a fecal indicator bacterial species monitored by the U.S. Environmental Protection Agency to assess microbial water quality. Due to the potential human health implications linked to high levels of <i>E. coli</i>, it is important to understand the inactivation or reduction mechanisms in surface waters. Our research examines the capacities of two types of widespread filter-feeding freshwater metazooplankton, <i>Daphnia magna</i> and <i>Brachionus calyciflorus</i>, to reduce <i>E. coli</i> concentrations. We examine the impacts of different environmentally relevant conditions on the clearance rates. Our results contribute to a better understanding of the importance of metazooplankton in controlling <i>E. coli</i> concentrations and what conditions will reduce or increase grazing. These results provide baseline data to support future efforts to develop a quantitative model relating zooplankton uptake rates to relevant environmental variables.