You are here:
The effect of protozoa source and sunlight on decay of fecal indicator bacteria and coliphages
Citation:
Korajkic, A., B. McMinn, AND V. Harwood. The effect of protozoa source and sunlight on decay of fecal indicator bacteria and coliphages. ASM Microbe 2023, Houston, TX, June 15 - 19, 2023.
Impact/Purpose:
Fecal indicator bacteria (FIB) have been used for over a century in the assessment of recreational water quality. Differences in survival characteristics of FIB and viral pathogens, common etiological agents in waterborne disease, signify the need for the additional research on their fate and transport characteristics in ambient waters.
Description:
Fecal indicator bacteria (FIB: Escherichia coli and enterococci) have a long history of use in recreational water quality assessment. However, differences in survival of FIB and enteric viruses, a leading cause of recreational waterborne disease outbreaks, suggests that viral indicators, such as somatic and F+ coliphage, could improve prediction of viral pathogens in recreational waters, but the impact of environmental factors, including predation, on their survival in water is poorly understood.Through removal of protozoan communities from either lake water or wastewater, we were able to investigate the effect of different grazer sources on decay rates of FIB and coliphage communities. Incubation under sunlight and shaded conditions enabled characterization of the relative influence of and interactions between predator source and ambient sunlight. Finally, a 14-day study was conducted in situ in a local lake, using submersible aquatic mesocosm device to mimic ambient conditions, to better characterize these interactions.FIB decay was generally greater than coliphages under all treatment conditions and was most rapid when indicators were exposed to lake protozoa and sunlight. The source of predators was more significant variable in FIB decay (p ≤ 0.004), especially during the first five days when it contributed 75-96% to the observed variability in the dataset. By comparison, sunlight was only influential in the later stages, contributing a maximum of 57% to FIB decay after 14 days. In contrast, somatic coliphage decayed fastest in the presence of wastewater protozoa and sunlight, but their decay under shaded conditions was ~ 10-fold less than F+ after 14 days. Protozoa source was a significant contributor (p ≤ 0.0174) to somatic coliphage decay through day eight (10-86%), while sunlight became influential in the later stages and contributed maximum 82% to decay after 14 days. F+ coliphage decay was the least affected by experimental variables, as protozoa source did not influence the decay and sunlight was only marginally significant. Protozoa source consistently contributed significantly to decay of FIB, and somatic, but not F+ coliphage. Sunlight generally accelerated decay, and shade reduced somatic coliphage decay to the lowest level among all the indicators. Differential responses of FIB, somatic, and F+ coliphages to environmental factors support the need for further studies that address the relationship between coliphages and viral pathogens under environmentally relevant conditions.
