Phylogenetic diversity of termite gut spirochaetes

A molecular phylogenetic analysis was done of not-yet-cultured spirochaetes inhabiting the gut of the termite, Reticulitermes flavipes (Kollar). Ninet y-eight clones of near-full-length spirochaetal 16S rDNA genes were classif ied by ARDRA pattern and by partial sequencing. All clones grouped within t he genus Treponema, and at least 21 new species of Treponema were recognize d within R. flavipes alone. Analysis of 190 additional clones from guts of Coptotermes formosanus Shiraki and Zootermopsis angusticollis (Hagen), as w ell as published data on clones from Cryptotermes domesticus (Haviland), Ma stotermes darwiniensis Froggatt, Nasutitermes lujae (Wasmann) and Reticulit ermes speratus(Kolbe), revealed a similar level of novel treponemal phyloge netic diversity in these representatives of five of the seven termite famil ies. None of the clones was closely related (i.e. all bore less than or equ al to 91% sequence similarity) to any previously recognized treponeme, The data also revealed the existence of two major phylogenetic groups of trepon emes: one containing all of the currently known isolates of Treponema and a large number of phylotypes from the human gingival crevice, but only a min ority of the termite gut spirochaete clones; another containing the majorit y of termite spirochaete clones and two Spirochaeta (S. caldaria and S. ste nostrepta), which, although free living, group within the genus Treponema o n the basis of 16S rRNA sequence. Signature nucleotides that almost perfect ly distinguished the latter group, herein referred to as the 'termite clust er', occurred at the following (E. coli numbering) positions: 289-G C-311; A at 812; and an inserted nucleotide at 1273. The emerging picture is that the long-recognized and striking morphological diversity of termite gut spi rochaetes is paralleled by their phylogenetic diversity and may reflect sub stantial physiological diversity as well.