We investigated the bacterial gut microbiota from 32 colonies of wood-feeding termites, comprising four Microcerotermes species (Termitidae) and four Reticulitermes species (Rhinotermitidae), using terminal restriction fragment length polymorphism analysis and clonal analysis of 16S rRNA. The obtained molecular community profiles were compared statistically between individuals, colonies, locations, and species of termites. Both analyses revealed that the bacterial community structure was remarkably similar within each termite genus, with small but significant differences between sampling sites and/or termite species. In contrast, considerable differences were found between the two termite genera. Only one bacterial phylotype (defined with 97% sequence identity) was shared between the two termite genera, while 18% and 50% of the phylotypes were shared between two congeneric species in the genera Microcerotermes and Reticulitermes, respectively. Nevertheless, a phylogenetic analysis of 228 phylotypes from Microcerotermes spp. and 367 phylotypes from Reticulitermes spp. with other termite gut clones available in public databases demonstrated the monophyly of many phylotypes from distantly related termites. The monophyletic "termite clusters" comprised of phylotypes from more than one termite species were distributed among 15 bacterial phyla, including the novel candidate phyla TG2 and TG3. These termite clusters accounted for 95% of the 960 clones analyzed in this study. Moreover, the clusters in 12 phyla comprised phylotypes from more than one termite (sub)family, accounting for 75% of the analyzed clones. Our results suggest that the majority of gut bacteria are not allochthonous but are specific symbionts that have coevolved with termites and that their community structure is basically consistent within a genus of termites.Termites harbor an abundance and diversity of gut bacteria, which are thought to play essential roles in the carbon and nitrogen metabolism of their host termites. While these characteristics of gut bacteria have been extensively studied by tracing the flow of carbon and nitrogen or characterizing isolated strains of bacteria (5, 25), the bacterial microbiota has remained a black box due to difficulties in cultivation of most of these bacteria. This has been an obstacle to a comprehensive understanding of symbiosis between gut bacteria and their host termites. Recently, we conducted a detailed census of the bacterial community in the gut of the termite Reticulitermes speratus by analyzing clones of 16S rRNA (18,19). We found 314 phylotypes (defined with 97.0% sequence identity) of 16S rRNA from 1,923 analyzed clones. The majority of the clones were affiliated with groups of anaerobic bacteria such as the genus Treponema and the orders Clostridiales and Bacteroidales, and most of the phylotypes were found for the first time. Many of them constituted novel lineages in several bacterial phyla, including the candidate phylum termite group I (TG1), which was one of the dominant groups in R. speratu...

The fungus-growing termites Macrotermes cultivate the obligate ectosymbiontic fungi, Termitomyces. While their relationship has been extesively studied, little is known about the gut bacterial symbionts, which also presumably play a crucial role for the nutrition of the termite host. In this study, we investigated the bacterial gut microbiota in two colonies of Macrotermes gilvus, and compared the diversity and community structure of bacteria among nine termite morphotypes, differing in caste and/or age, using terminal restriction fragment length polymorphism (T-RFLP) and clonal analysis of 16S rRNA. The obtained molecular community profiles clustered by termite morphotype rather than by colony, and the clustering pattern was clearly more related to a difference in age than to caste. Thus, we suggest that the bacterial gut microbiota change in relation to the food of the termite, which comprises fallen leaves and the fungus nodules of Termitomyces in young workers, and leaves degraded by the fungi, in old workers. Despite these intracolony variations in bacterial gut microbiota, their T-RFLP profiles formed a distinct cluster against those of the fungus garden, adjacent soil and guts of sympatric wood-feeding termites, implying a consistency and uniqueness of gut microbiota in M. gilvus. Since many bacterial phylotypes from M. gilvus formed monophyletic clusters with those from distantly related termite species, we suggest that gut bacteria have co-evolved with the termite host and form a microbiota specific to a termite taxonomic and/or feeding group, and furthermore, to caste and age within a termite species.

Recently we discovered two novel, deeply branching lineages in the domainHere, we report on the specific detection of these bacteria, the candidate phylum TG3 (Termite Group 3) and a subphylum in the phylum Fibrobacteres, by fluorescence in situ hybridization in the guts of the wood-feeding termites Microcerotermes sp. and Nasutitermes takasagoensis. Both bacterial groups were detected almost exclusively from the luminal fluid of the dilated portion in the hindgut. Each accounted for approximately 10% of the total prokaryotic cells, constituting the second-most dominant groups in the whole-gut microbiota. The detected cells of both groups were in undulate or vibroid forms and apparently resembled small spirochetes. The cell sizes were 0.2 to 0.4 by 1.3 to 6.0 m and 0.2 to 0.3 by 1.3 to 4.9 m in the TG3 and Fibrobacteres, respectively. Using PCR screenings with specific primers, we found that both groups are distributed among various termites. The obtained clones formed monophyletic clusters that were delineated by the host genus rather than by the geographic distance, implying a robust association between these bacteria and host termites. TG3 clones were also obtained from a cockroach gut, lake sediment, rice paddy soil, and deep-sea sediments. Our results suggest that the TG3 and Fibrobacteres bacteria are autochthonous gut symbionts of various termites and that the TG3 members are also widely distributed among various other environments.Termites harbor an abundance and diversity of gut bacteria, which are thought to play essential roles in the carbon and nitrogen metabolism of their host termites (4, 26). Recent culture-independent analyses have revealed that the bacterial gut microbiota comprises many termite-specific lineages that are as yet uncultured (11-13, 27, 33, 35, 39). Among them, the candidate phylum Termite Group I (TG1) was first recognized in our previous study as a novel, deeply branching lineage specific to termites (27) and later found to constitute a new phylum, together with clones from various environments (13, 15). Now, the termite-specific cluster in this candidate phylum has been partly characterized as endosymbionts of gut protists in various lower termites (28, 38), whereas no isolate exists so far from this phylum. In higher termites, which generally lack gut symbiotic protists and harbor only prokaryotes (in contrast to lower termites that harbor both), there have been found other novel, deeply branching lineages in the domain Bacteria.Using clonal analyses of 16S rRNA, we recently discovered a novel phylum-level cluster, temporarily named TG3 (Termite Group 3), and a novel subphylum-level cluster in the phylum Fibrobacteres (designated Fibrobacteres subphylum 2 in this study) from the guts of the wood-feeding higher termites Microcerotermes spp. (11). Each group accounted for approximately 10% of the analyzed clones, constituting the second-most dominant groups, together with the orders Bacteroidales and Clostridiales, following the predominant genus, Treponema. The candidate phylum...

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