SSU rRNA genes of symbiotic methanogens in the hindgut of four lower Japanese termites and one Australian lower termite Mastotermes darwiniensis as well as a soil sample collected near a nest of Reticulitermes speratus were amplified, cloned and phylogenetically analyzed. Most of the clones found in the lower termites were of the genus Methanobrevibacter. The symbiotic methanogens in the Japanese termites and in the soil sample were related to each other. The clones obtained from M. darwiniensis grouped separately from the clones of Japanese termites. These results suggest that the methanogen community of lower termites reflects host locality rather than phylogeny.Key words: symbiosis, termite, methanogen, phylogeny, ThermoplasmaTermites harbor methanogenic archaea in the hindgut 9) , where methane is formed by the reduction of carbon-dioxide with hydrogen. Methanogens and acetogens in the termite hindgut play a role as a hydrogen-sink. The hydrogenconsuming process facilitates the anaerobic degradation of lignocellulose 14) . The microecology of the termite gut was recently reviewed 1) .A phylogenetic analysis of methanogens in the hindgut of the lower termite Reticulitermes speratus by Ohkuma et al. 11) found only one type of sequence in PCR clones. We have also analyzed symbiotic methanogens in the hindgut of R. speratus 15) . PCR clones of SSU rDNA sequences were grouped into three types. Type 1 clones were further classified into subtypes 1A, 1B, 1C and 1D. Most of the PCR clones of methanogen in R. speratus collected around the Japan Archipelago belonged to subtypes 1A and 1B in the genus Methanobrevibacter. Fluorescence in situ hybridization analysis showed that at least some of the type 1 species live on the hindgut epithelial surface. Ohkuma et al. 10,12) have reported two other types of sequences, Cd30 and MHj4, from Cryptotermes domesticus and Hodotermopsis sjostedti, respectively. Leadbetter et al. 5,6) have isolated three species of Methanobrevibacter, M. curvatus, M. cuticularis, and M. filiformis from R. flavipes. In the present study, we examined the molecular phylogeny of symbiotic methanogens of five species that belong to four families of lower termites. Phylogenetic relationships between methanogens and host termites were also discussed.Four lower termite species of three families, Neotermes koshunensis, Hodotermopsis sjostedti, Reticulitermes kanmonensis, and Coptotermes formosanus, were collected in the Japan Archipelago. Sampling points of the Japanese termites are listed in Table 1. Another lower termite Mastotermes darwiniensis was collected in Australia and kindly donated by Dr. O. Kitade. Ten individuals of pseudergate (worker) from each colony of termite were employed for DNA extraction. Total genomic DNA of the digestive tracts of the termites was prepared as described previously 15) . PCR primers and reaction conditions were also described in a previous report 15) . The primers used were ME855F and ME1354R, which were designed to se-