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, isolated from the rhizoplane of an aquatic plant (a reed, Phragmites australis) inhabiting a freshwater lake in Japan, was morphologically, physiologically and phylogenetically characterized. Strain T wasGram-negative and ovoid to rod-shaped, and formed pinkish hard colonies on agar plates. Strain YO-36 T grew at 20-40 6C with optimum growth at 30-35 6C, whilst no growth was observed at 15 6C or 45 6C. The pH range for growth was 5.5-8.5 with an optimum at pH 6.5. Strain YO-36T utilized a limited range of substrates, such as sucrose, gentiobiose, pectin, gellan gum and xanthan gum. The strain contained C 16 : 0 , C 16 : 1 , C 14 : 0 and C 15 : 0 as the major cellular fatty acids and menaquinone-12 as the respiratory quinone. The G+C content of the genomic DNA was 62.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YO-36 T belonged to the candidate phylum OP10 comprised solely of environmental 16S rRNA gene clone sequences except for two strains, P488 and T49 isolated from geothermal soil in New Zealand; strain YO-36 T showed less than 80 % sequence similarity to strains P488 and T47.

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We constructed a bacterial 16S rRNA gene clone library from the gut microbial community of O. formosanus and phylogenetically analyzed it in order to contribute to the evolutional study of digestive symbiosis and method development for termite control. After screening by restriction fragment length polymorphism (RFLP) analysis, 56 out of 280 clones with unique RFLP patterns were sequenced and phylogenetically analyzed. The representative phylotypes were affiliated to four phylogenetic groups, Firmicutes, the Bacteroidetes/ Chlorobi group, Proteobacteria, and Actinobacteria of the domain Bacteira. No one clone affiliated with the phylum Spirochaetes was identified, in contrast to the case of wood-feeding termites. The phylogenetic analysis revealed that nearly half of the representative clones (25 phylotypes) formed monophyletic clusters with clones obtained from other termite species, especially with the sequences retrieved from fungus-growing termites. These results indicate that the presence of termitespecific bacterial lineages implies a coevolutional relationship of gut microbes and host termites.Key words: termite; bacteria; symbiosis; 16S rRNA; restriction fragment length polymorphismTermites live in the area from tropical to temperate zones in great abundance, and are capable of degrading various derivatives of plant materials (woods, leaves, and humus). They have a great impact on the decomposition of plant matter in nature, and play an important role, especially in the carbon cycle. On the other hand, termites are known to be a harmful insect causing damage to farm products, wooden houses, etc. The xylophagy of termites depends on digestive symbiosis established in their hindgut, which consists of both eukaryotes (protozoa and fungi) and prokaryotes (bacteria and archaea). The microbial symbionts in termite guts play an important role in lignocellulose digestion and termite nutrition, and this mutualism has been referred to as a representative model of symbiotic association between animals and microorganisms.1)The microflora of termite guts are commonly exchanged between colony members and transmitted to the next generation via trophallaxis (proctodeal feeding), which can promote coevolutional diversification of symbiotic microbes along with the host phylogeny. Protozoan symbionts residing in classificatory lower termites are responsible for lignocellulose digestion in this termite group. They are basically host termite specific in phylogeny and composition, reflecting the obligate (mutualistic) symbiotic association between the protists and termites.2) However, the evolutional relationships between symbiotic prokaryotes and host termites have not yet been adequately addressed, because of their enormous population and diversity.For the last decade, microbial communities of termite guts have been investigated by rRNA gene-based molecular techniques, and our knowledge of this symbiosis has been expanded considerably. [3][4][5][6][7][8] Recently, Hongoh et al. 9) performed comparative analysis of the b...