Indigenous Microbiota and Habitat Influence Escherichia coli Survival More than Sunlight in Simulated Aquatic Environments

The reported fate ofEscherichia coli in the environment ranges from extended persistence to rapid decline. Incomplete understanding of factors that influence survival hinders risk assessment and modeling of the fate of fecal indicator bacteria (FIB) and pathogens. FIB persistence in subtropical aquatic environments was explored in outdoor mesocosms inoculated with fiveE. coli strains. The manipulated environmental factors were (i) presence or absence of indigenous microbiota (attained by natural, disinfected, and cycloheximide treatments), (ii) freshwater versus seawater, and (iii) water column versus sediment matrices. When indigenous microbes were removed (disinfected),E. coli concentrations decreased little despite exposure to sunlight. Conversely, under conditions that included the indigenous microbiota (natural), significantly greater declines inE. coli occurred regardless of the habitat. The presence of indigenous microbiota and matrix significantly influencedE. coli decline, but their relative importance differed in freshwater versus seawater. Cycloheximide, which inhibits protein synthesis in eukaryotes, significantly diminished the magnitude ofE. coli decline in water but not in sediments. The inactivation of protozoa and bacterial competitors (disinfected) caused a greater decline inE. coli than cycloheximide alone in water and sediments. These results indicate that the autochthonous microbiota are an important contributor to the decline ofE. coli in fresh and seawater subtropical systems, but their relative contribution is habitat dependent. This work advances our understanding of how interactions with autochthonous microbiota influence the fate ofE. coli in aquatic environments and provides the framework for studies of the ecology of enteric pathogens and other allochthonous bacteria in similar environments.