1. School of Information and Computer Sciences, Institute for Genomics and Bioinformatics, University of California, Irvine, Irvine, California 92697-3435, School of Biological Sciences, University of California, Irvine, Irvine, California 92697-1450, and Microbiology Division, Instituto de Biología Molecular y Celular de Rosario (IBR), Universidad Nacional de Rosario, Suipacha 531, Rosario, Argentina