Phylogenetic relationships of symbiotic spirochetes in the gut of diverse termites

Phylogenetic relationships of symbiotic spirochetes in the gut of diverse termites were analyzed without cultivation of these microorganisms. A portion of the 16S rDNA (ca. 850 bp) was amplified directly from DNA of the mixed population in the gut by PCR and cloned. A total of 30 spirochetal phylotypes affiliated with the treponemes were identified from four termite species and they were compared with those already reported from other termites. They represented separate lines of descent from any known species of Treponema, and they were divided into two discrete clusters; one was related to Spirochaeta stenostrepta and S. caldaria, and the other was grouped together with members of the Treponema bryantii subgroup. Although some sequences from evolutionarily related termites showed close similarity, most of the sequences of spirochetes were dissimilar among different termite species, and spirochetal sequences from a single termite species occurred in several distinct phylogenetic positions. These findings suggest that termites constitute a rich reservoir of novel spirochetal diversity and that evolution of the symbiosis is not simple.