PULSED-FIELD GEL-ELECTROPHORESIS OF GENOMIC DIGESTS OF THERMUS STRAINS AND ITS IMPLICATIONS FOR TAXONOMIC AND EVOLUTIONARY STUDIES

Pulsed-field electrophoresis (PFGE) of the SspI genomic digests of 14 Thermus isolates showed that each one had a unique restriction enzyme digestion pattern. A group of New Zealand strains showed some shared b ands, but each isolate gave essentially a unique fingerprint. In addit ion, evolutionary distances between Thermus strains estimated by using PPGE restriction fragment length polymorphisms (PFGE-RFLPs) correlate well with those based on small-subunit rRNA sequence data. As a conse quence, the phylogenetic trees constructed on the basis of PFGE-RFLPs and those constructed by using small-subunit rRNA sequences generally agree. On the basis of the evolutionary distances estimated by using P FGE-RFLPs, the estimated average genomic rate of divergence for Thermu s spp. is approximately 0.27% per million years.