1. U.S. Geological Survey (USGS), Menlo Park, CA 94025, USA.
2. Department of Microbiology, Southern Illinois University, Carbondale, IL 62901, USA.
3. Department of Marine Sciences, University of Georgia, Athens, GA 30602, USA.
4. Department of Biological Sciences, Duquesne University, Pittsburgh, PA 15282, USA.
5. USGS Water Sciences Center, Augusta, ME 04330, USA.