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Appl. Environ. Microbiol. doi:10.1128/AEM.02654-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Presence and Sources of Fecal Coliform Bacteria in Epilithic Periphyton Communities of Lake Superior

Department of Biology, University of Minnesota Duluth, Duluth, MN; Department of Soil, Water and Climate and; BioTechnology Institute, University of Minnesota, St. Paul, MN

^* To whom correspondence should be addressed. Email: rhicks{at}d.umn.edu.

	Abstract

Epilithic periphyton communities were sampled at three sites on the Minnesota shoreline of Lake Superior from June 2004 to August 2005 to determine if fecal coliforms and Escherichia coli were present throughout the ice-free season. Fecal coliforms densities increased up to 4 orders of magnitude in early summer, reached peaks of up to 1.4 x 10⁵ CFU cm^-2 by late July, and decreased during autumn. Horizontal, fluorophore-enhanced rep-PCR (HFERP) DNA fingerprint analyses indicated that the source for 2% to 44% of the E. coli isolated from these periphyton communities could be identified when compared with a library of E. coli fingerprints from animal hosts and sewage. Waterfowl were the major source (68-99%) of periphyton E. coli that could be identified. Several periphyton E. coli isolates were genotypically identical (92% similarity), repeatedly isolated over time, and unidentified when compared to the source library, suggesting these strains were naturalized members of periphyton communities. If the unidentified E. coli strains from periphyton were added to the known source library, then 57% to 81% of E. coli from overlying waters could be identified with waterfowl (15-67%), periphyton (6-28%) and sewage effluent (8-28%) being the major potential sources. Inoculated E. coli rapidly colonized natural periphyton in laboratory microcosms, persisted for several weeks, and some cells were released to the overlying water. Our results indicate that E. coli from periphyton released into waterways confounds the use of this bacterium as a reliable indicator of recent fecal pollution.