Differential Effects of Zooplankton on Sunlight Inactivation of Viruses

Interactions between viruses and filter-feeding zooplankton can alter viral persistence in surface waters, with direct implications for water quality and public health risk. However, data on virus-zooplankton interactions and the environmental factors that influence them are still limited. This study evaluated the impact of filter feeding, in the dark and under simulated sunlight, on a bacteriophage (MS2) and a human virus (echovirus11; E11) in the presence of a ciliate (Tetrahymena pyriformis) and rotifer (Brachionus calyciflorus). Dark experiments established organism-dependent baseline removal for each virus, and rotifers showed greater removal of both viruses in comparison to ciliates. Under simulated sunlight, in contrast, experiments with ciliates resulted in greater virus removal compared to experiments with rotifers over a similar timespan (4.2 vs 2.7 log MS2 in 53-58 h; 3.5 vs 3.0 log E11 in 24-25 h). Analysis of decay rate constants reveals species-specific shifts in virus removal between dark and light that, depending on viral type and zooplankton species, either accelerate viral attenuation or protect viruses and prolong infectivity. T. pyriformis increases removal under sunlight relative to dark conditions and acts synergistically with sunlight inactivation, whereas rotifers impede sunlight inactivation. These data address important knowledge gaps on how dark biotic processes can modulate sunlight-mediated inactivation. The reported decay constants can help inform predictions of virus environmental fate with implications for natural and engineered treatment systems that rely on sunlight disinfection to inactivate viruses.