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 bands, but each isolate gave essentially a unique fingerprint. In addition, 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 consequence, 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 PFGE-RFLPs, the estimated average genomic rate of divergence for Thermus spp. is approximately 0.27% per million years.