16S-rDNA analysis of Spirochaeta thermophila: Its phylogenetic position and implications for the systematics of the order Spirochaetales

The 16S rRNA gene of Spirochaeta thermophila DSM 6578 was amplifed by the polymerase chain reaction and analysis of a 1333 nucleotide long stretch performed. The sequence was aligned to the homologous region of 13 representatives from six spirochete genera, and the phylogenetic position of S. thermophila determined. This species constitutes a deep-branching member of a cluster that is defined by representatives of Spirochaeta and Treponema and by Borellia burgdorferi. The genera Serpulina, Leptonema and Leptospira are more ancient representatives of the spirochete line of descent. The branching pattern confirms earlier results of phylogenetic studies which showed the genus Spirochaeta to be heterogeneous, with S. zuelzerae and S. stenostrepta displaying a higher degree of relatedness to treponemas than to the main (authentic) Spirochaeta group