PHYLOGENY OF HUMAN INTESTINAL SPIROCHETES INFERRED FROM 16S RDNA SEQUENCE COMPARISONS

The sequence of 1383 nucleotides of the DNA encoding 16S rDNA was dete rmined for strains of human intestinal spirochaetes, comprising an unn amed isolate and ''Brachyspira aalborgi'' NCTC 11492. A phylogenetic t ree was inferred from aligned sequence comparisons between the intesti nal spirochaetes, representatives of the Spirochaetales and Escherichi a coli. The type strain of Brachyspira aalborgi, though related to the Serpulina spp. at approx. 96.5% sequence similarity was distinct and separated from the unnamed human intestinal isolate, HIS Oman, N26. Th e latter formed a separated and novel lineage that bisected the Spiroc haetales.