Phylogenetic relationships of symbiotic methanogens in diverse termites

Termites harbor symbiotic microorganisms in their gut which emit methane. T he phylogeny of the termite methanogens was inferred without cultivation ba sed on nucleotide sequences of PCR-amplified 16S ribosomal RNA genes. Seven methanogen sequences from four termite species were newly isolated, and to gether with those previously published, these sequences were phylogenetical ly compared. The termite methanogen sequences were divided into three clust ers. Two clusters of sequences, derived from the gut DNA of so-called highe r termites, were related to methanogens in the orders Methanosarcinales or Methanomicrobiales. All of the sequences in the case of lower termites were closely related to the genus Methanobrevibacter. However, most of the term ite symbionts were found to be distinct from known methanogens. They are no t dispersed among diverse methanogen species, but rather formed unique line ages in the phylogenetic trees. (C) 1999 Federation of European Microbiolog ical Societies. Published by Elsevier Science B.V. All rights reserved.