REDUCED THERMOPHILIC BIAS IN THE 16S RDNA SEQUENCE FROM THERMUS RUBERPROVIDES FURTHER SUPPORT FOR A RELATIONSHIP BETWEEN THERMUS AND DEINOCOCCUS

The 16S ribosomal (r) DNA from Thermus ruber and three new species of Thermus was amplified and sequenced using the PCR. The sequence from T hermus ruber shows much lower thermophilic bias than the other Thermus sequences as judged by base composition ratios and a chi2 heterogenei ty test. Its inclusion in phylogenetic analyses gives a topology which consistently groups Thermus and Deinococcus as sister taxa. This rela tionship is recovered despite opposing compositional bias in base comp osition and without the need to restrict the analysis to certain sites (other than those which could not be aligned). The topology is suppor ted by analysis of base substitutions which show a lower ratio of tran sversions to transitions between sequences from Thermus spp. and Deino coccus radiodurans, than between these sequences and sequences from re ference thermophiles and mesophiles.