Microbial Communities and the Diverse Ecology of Fecal Indicators at Lake Michigan Beaches

Abstract

Fecal indicator bacteria (FIB) such as Escherichia coli (E. coli) and enterococci are used to assess microbiological water quality in recreational waters. The use of FIB follows the assumption that their presence correlates with that of fecal-associated pathogens in recreational waters. The beach ecosystem is complex however and multiple factors can influence the concentration of E. coli and enterococci in the beach environment. Microbial communities within beach sand play a key role in nutrient cycling and are important to the nearshore ecosystem function. E. coli and enterococci, two common indicators of fecal pollution, have been shown to persist in the beach sand, but little is known about how microbial community assemblages are related to these fecal indicator bacteria (FIB) reservoirs. The first objective of this project was to harness the power of next-generation sequencing to profile the indigenous communities within beach sand and examine key environmental drivers of community structure. FIB were found at similar levels in sand at beaches adjacent to urban, forested, and agricultural land and in both the berm and backshore. However, there were striking differences in the berm and backshore microbial communities, even within the same beach, reflecting the very different environmental conditions in these beach zones in which FIB can survive. Results indicate that microbial community structure in beach sand is most associated with the concentrations of total organic carbon (TOC) and total phosphorus (TP). Fine scale nucleotide differences in the V4V5 region of the 16S rRNA gene of abundant taxa were identified and sequence patterns suggest a biogeographic influence. This work demonstrates that microbial communities are reflective of environmental conditions at freshwater beaches and are able to provide useful information regarding long-term anthropogenic stress. The second objective of this project was to use host-specific alternative fecal indicator assays to identify the major pollution sources that are responsible for contributing high levels of E. coli in both beach sand and water. At the six beaches studied, berm sand contained the highest levels of E. coli versus to water (P