No abstract

Fungus-growing termites have a mutualistic relationship with their cultivated fungi. To improve understanding of genetic aspects of this relationship, we examined molecular markers in the fungus-growing termite Odontotermes formosanus and its fungi Termitomyces spp. from the Ryukyu Archipelago. Based on the polymorphic band patterns obtained from arbitrarily primed polymerase chain reaction methods, we constructed cladograms for related colonies of the termites and fungi. The resulting trees indicated that the termites display little genetic variation among the colonies, while the symbiotic fungi consist of two major genetic types. In addition, molecular phylogenetic trees of the symbiotic fungi based on internal transcribed spacer and 18S rDNA suggested that these two types of fungi are different species. We also demonstrated that the fungi comprising the fruiting bodies and fungus combs are identical, and that fungus combs are probably a monoculture within a single termite colony. Our results indicate that horizontal transmission of symbiotic fungi among termite colonies occurred during the evolutionary history of this symbiosis.

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...