Abstract 1612 Comparison of Experimental and Predicted Carbon Utilization Profiles of Escherichia coli Populations Isolated from a Hypereutrophic Watershed System

Strict regulations exist for Escherichia coli in recreational waters, stemming from the canonical assumption that E. coli is primarily found in the digestive systems of animals and the implication that its presence in the environment is a result of fecal contamination. We report on E. coli populations isolated as part of a multi-year study of impacts of urbanization and agriculture on the Macatawa watershed. Located in southwest Michigan, Lake Macatawa is a small eutrophic drowned river mouth lake that drains into Lake Michigan and is part of the 175 sq mi Macatawa watershed of eight sub-basins. The lake and streams have high sediment, nutrient and coliform loading and are part of ongoing remediation efforts led by the local community. As part of longitudinal monitoring of the Macatawa Watershed, we have isolated over 10,000 strains of water-derived E. coli and sequenced over 500 strains. This represents a novel data set of water-derived E. coli genomes that can be used to address the hypothesis that endemic E. coli populations exist in recreational waters outside of the mammalian gut. We have characterized the carbon source utilization in this population in order to understand potential differences between mammalian-derived and water-derived E. coli strains through experimental and computational methods. We experimentally determined the growth properties of 32 watershed strains and one reference laboratory strain (E. coli MG1655) on 192 substrates provided as sole carbon sources using Biolog™ PM1 and PM2a plates. In parallel, we generated genome scale metabolic models of the sequenced watershed strains using ModelSEED2 and analyzed predicted carbon source utilization in context with experimentally determined metabolic profiles. Results indicate a high level of metabolic diversity in the water-derived strains. Ordination analyses summarizing the growth characteristics of all strains on all substrates demonstrated that all water-derived strains were distinct from the laboratory strain. Distinct groups of water-derived strains were also observed associated with temporal factors of sampling (e.g., year and season). These results lend support to the hypothesis that endemic strains of E. coli exist in recreational waters that are not indicative of fecal contamination and that there are temporal dynamics associated with functional diversity in this population. This has implications for current regulatory monitoring approaches of recreational waters for public health purposes and improves our understanding of metabolic diversity in closely related strains of bacteria. Funding support is gratefully acknowledged from the National Science Foundation (MRI and MCB), Project Clarity/Outdoor Discovery Center, Herbert H. and Grace A. Dow Foundation, and the A. Paul Schaap endowed research fund.