1. Department of Civil Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3109, Microbiology Department, Washington State University, 387 Eastlick, Pullman, Washington 99164-4233, and Interfacial Geochemistry and Environmental Microbiology Groups, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352