Cospeciation of termite gut flagellates and their bacterial endosymbionts: Trichonympha species and 'Candidatus Endomicrobium trichonymphae'

Symbiotic flagellates play a major role in the digestion of lignocellulose in the hindgut of lower termites. Many termite gut flagellates harbour a distinct lineage of bacterial endosymbionts, so-called Endomicrobia, which belong to the candidate phylum Termite Group 1. Using an rRNA-based approach, we investigated the phylogeny of Trichonympha , the predominant flagellates in a wide range of termite species, and of their Endomicrobia symbionts. We found that Trichonympha species constitute three well-supported clusters in the Parabasalia tree. Endomicrobia were detected only in the apical lineage (Cluster I), which comprises flagellates present in the termite families Termopsidae and Rhinotermitidae, but apparently absent in the basal lineages (Clusters II and III) consisting of flagellates from other termite families and from the wood-feeding cockroach, Cryptocercus punctulatus . The endosymbionts of Cluster I form a monophyletic group distinct from many other lineages of Endomicrobia and seem to have cospeciated with their flagellate host. The distribution pattern of the symbiotic pairs among different termite species indicates that cospeciation of flagellates and endosymbionts is not simply the result of a spatial separation of the flagellate lineages in different termite species, but that Endomicrobia are inherited among Trichonympha species by vertical transmission. We suggest extending the previously proposed candidatus name ' Endomicrobium trichonymphae ' to all Endomicrobia symbionts of Trichonympha species, and estimate that the acquisition by an ancestor of Trichonympha Cluster I must have occurred about 40–70 million years ago, long after the flagellates entered the termites.     

Hidden cellulases in termites: revision of an old hypothesis

The intestinal flagellates of termites produce cellulases that contribute to cellulose digestion of their host termites. However, 75% of all termite species do not harbour the cellulolytic flagellates; the endogenous cellulase secreted from the midgut tissue has been considered a sole source of cellulases in these termites. Using the xylophagous flagellate-free termites Nasutitermes takasagoensis and Nasutitermes walkeri, we successfully solubilized cellulases present in the hindgut pellets. Zymograms showed that the hindguts of these termites possessed several cellulases and contained up to 59% cellulase activity against crystalline cellulose when compared with the midgut. Antibiotic treatment administered to N. takasagoensis significantly reduced cellulase activity in the hindgut, suggesting that these cellulases were produced by symbiotic bacteria.     

Ancestral transfer of symbionts between cockroaches and termites: an alternative hypothesis.

Closely related cellulolytic protozoa reside in the hindguts of extant woodroaches (Cryptocercidae) and termites (Isoptera). The evolutionary origin of these symbiotic relationships in the two lineages is uncertain. Transfer of protozoa between ancestors of modern Cryptocercus and termites remains a valid alternative theory to the established hypothesis of symbiont inheritance from a common ancestor. Nalepa's (Proc. R. Soc. Lond. B 246, 185 (1991] concerns regarding the protozoan transfer hypothesis focus on the biology of modern species, and neglect to consider the evolutionary framework of an ancestral dynamic postulated to occur among Palaeozoic insects. Legitimacy of the symbiont transfer theory removes the constraint of interpreting presence of cellulolytic protozoa as a synapomorphy between Cryptocercidae and Isoptera, with potential impact on objective resolution of dictyopteran phylogeny.     

Identification and characterization of ectosymbionts of distinct lineages in Bacteroidales attached to flagellated protists in the gut of termites and a wood-feeding cockroach

Bacterial attachments to nearly the entire surface of flagellated protists in the guts of termites and the wood-feeding cockroach Cryptocercus are often observed. Based on the polymerase chain reaction-amplified 16S rRNA gene sequences, we investigated the phylogenetic relationships of the rod-shaped, attached bacteria (ectosymbionts) of several protist species from five host taxa and confirmed their identity by fluorescence in situ hybridizations. These ectosymbionts are affiliated with the order Bacteroidales but formed three distinct lineages, each of which may represent novel bacterial genera. One lineage consisted of the closely related ectosymbionts of two species of the protist genus Devescovina (Cristamonadida). The second lineage comprised three phylotypes identified from the protist Streblomastix sp. (Oxymonadida). The third lineage included ectosymbionts of the three protist genera Hoplonympha, Barbulanympha and Urinympha in the family Hoplonymphidae (Trichonymphida). The ultrastructural observations indicated that these rod-shaped ectosymbionts share morphological similarities of their cell walls and their point of attachment with the protist but differ in shape. Elongated forms of the ectosymbionts appeared in all the three lineages. The protist cells Streblomastix sp. and Hoplonympha sp. display deep furrows and vane-like structures, but these impressive structures are probably evolutionarily convergent because both the host protists and their ectosymbionts are distantly related.     

The candidate phylum 'Termite Group 1' of bacteria: phylogenetic diversity, distribution, and endosymbiont members of various gut flagellated protists

The candidate phylum 'Termite Group 1' (TG1) of bacteria, which is abundant in termite guts but has no culturable representative, was investigated with respect to the in situ localization, distribution, and diversity. Based on the 16S rRNA gene sequence analyses and FISH in termite guts, a number of lineages of TG1 members were identified as endosymbionts of a variety of gut flagellated protists from the orders Trichonymphida, Cristamonadida, and Oxymonadida that are mostly unique to termites. However, the survey in various environments using specific PCR primers revealed that TG1 members were also present in termites, a cockroach, and the bovine rumen that typically lack these protist orders. Most of the TG1 members from gut flagellates, termites, cockroaches, and the rumen formed a monophyletic subcluster that showed a shallow branching pattern in the phylogenetic tree, suggesting their recent diversification. Although endosymbionts of the same protist genera tended to be closely related, the endosymbiont lineages were often independent of the higher level classifications of their host protist and were dispersed in the phylogenetic tree. It appears that their cospeciation is not the sole rule for the diversification of TG1 members of endosymbionts.     

Diversification of endosymbiosis: replacements,co-speciation and promiscuity of bacteriocyte symbionts in weevils

The processes and mechanisms underlying the diversification of host–microbe endosymbiotic associations are of evolutionary interest. Here we investigated the bacteriocyte-associated primary symbionts of weevils wherein the ancient symbiont Nardonella has experienced two independent replacement events: once by Curculioniphilus symbiont in the lineage of Curculio and allied weevils of the tribe Curculionini, and once by Sodalis-allied symbiont in the lineage of grain weevils of the genus Sitophilus. The Curculioniphilus symbiont was detected from 27 of 36 Curculionini species examined, the symbiont phylogeny was congruent with the host weevil phylogeny, and the symbiont gene sequences exhibited AT-biased nucleotide compositions and accelerated molecular evolution. These results suggest that the Curculioniphilus symbiont was acquired by an ancestor of the tribe Curculionini, replaced the original symbiont Nardonella, and has co-speciated with the host weevils over evolutionary time, but has been occasionally lost in several host lineages. By contrast, the Sodalis-allied symbiont of Sitophilus weevils exhibited no host–symbiont co-speciation, no AT-biased nucleotide compositions and only moderately accelerated molecular evolution. These results suggest that the Sodalis-allied symbiont was certainly acquired by an ancestor of the Sitophilus weevils and replaced the original Nardonella symbiont, but the symbiotic association must have experienced occasional re-associations such as new acquisitions, horizontal transfers, replacements and/or losses. We detected Sodalis-allied facultative symbionts in populations of the Curculionini weevils, which might represent potential evolutionary sources of the Sodalis-allied primary symbionts. Comparison of these newcomer bacteriocyte-associated symbiont lineages highlights potential evolutionary trajectories and consequences of novel symbionts after independent replacements of the same ancient symbiont.     

Several deep-sea mussels and their associated symbionts are able to live both on wood and on whale falls

Bathymodiolin mussels occur at hydrothermal vents and cold seeps, where they thrive thanks to symbiotic associations with chemotrophic bacteria. Closely related genera Idas and Adipicola are associated with organic falls, ecosystems that have been suggested as potential evolutionary 'stepping stones' in the colonization of deeper and more sulphide-rich environments. Such a scenario should result from specializations to given environments from species with larger ecological niches. This study provides molecular-based evidence for the existence of two mussel species found both on sunken wood and bones. Each species specifically harbours one bacterial phylotype corresponding to thioautotrophic bacteria related to other bathymodiolin symbionts. Phylogenetic patterns between hosts and symbionts are partially congruent. However, active endocytosis and occurrences of minor symbiont lineages within species which are not their usual host suggest an environmental or horizontal rather than strictly vertical transmission of symbionts. Although the bacteria are close relatives, their localization is intracellular in one mussel species and extracellular in the other, suggesting that habitat choice is independent of the symbiont localization. The variation of bacterial densities in host tissues is related to the substrate on which specimens were sampled and could explain the abilities of host species to adapt to various substrates.     

Diet is the primary determinant of bacterial community structure in the guts of higher termites

The gut microbiota of termites plays critical roles in the symbiotic digestion of lignocellulose. While phylogenetically ‘lower termites’ are characterized by a unique association with cellulolytic flagellates, higher termites (family Termitidae) harbour exclusively prokaryotic communities in their dilated hindguts. Unlike the more primitive termite families, which primarily feed on wood, they have adapted to a variety of lignocellulosic food sources in different stages of humification, ranging from sound wood to soil organic matter. In this study, we comparatively analysed representatives of different taxonomic lineages and feeding groups of higher termites to identify the major drivers of bacterial community structure in the termite gut, using amplicon libraries of 16S rRNA genes from 18 species of higher termites. In all analyses, the wood‐feeding species were clearly separated from humus and soil feeders, irrespective of their taxonomic affiliation, offering compelling evidence that diet is the primary determinant of bacterial community structure. Within each diet group, however, gut communities of termites from the same subfamily were more similar than those of distantly related species. A highly resolved classification using a curated reference database revealed only few genus‐level taxa whose distribution patterns indicated specificity for certain host lineages, limiting any possible cospeciation between the gut microbiota and host to short evolutionary timescales. Rather, the observed patterns in the host‐specific distribution of the bacterial lineages in termite guts are best explained by diet‐related differences in the availability of microhabitats and functional niches.     

Wood-feeding cockroaches as models for termite evolution (Insecta: Dictyoptera): Cryptocercus vs. Parasphaeria boleiriana

Isoptera are highly specialized cockroaches and are one of the few eusocial insect lineages. Cryptocercus cockroaches have appeared to many as ideal models for inference on the early evolution of termites, due to their possible phylogenetic relationship and several shared key attributes in life history. Recently, Pellens, Grandcolas, and colleagues have proposed the blaberid cockroach Parasphaeria boleiriana to be an alternative model for the early evolution in termites. We compare the usefulness of Cryptocercus and P. boleiriana as models for termite evolution. Cryptocercus and lower Isoptera (1) can both feed on comparatively recalcitrant wood, (2) have an obligate, rich and unique hypermastigid and oxymonadid fauna in the hindgut, (3) transfer these flagellates to the next generation by anal trophallaxis, (4) have social systems that involve long-lasting biparental care, and, finally, (5) are strongly suggested to be sister groups, so that the key attributes (1)-(4) appear to be homologous between the two taxa. On the other hand, P. boleiriana (1) feeds on soft, ephemeral wood sources, (2) shows no trace of the oxymonadid and hypermastigid hindgut fauna unique to Cryptocercus and lower Isoptera, nor does it have any other demonstrated obligate relationship with hindgut flagellates, (3) is likely to lack anal trophallaxis, (4) has only a short period of uniparental brood care, and (5) is phylogenetically remote from the Cryptocercus+Isoptera clade. These facts would argue against any reasonable usage of P. boleiriana as a model for the early evolution of Isoptera or even of the clade Cryptocercus+Isoptera. Cryptocercus thus remains an appropriate model-taxon-by-homology for early termite evolution. As compared to P. boleiriana, some other Blaberidae (such as the Panesthiinae Salganea) appear more useful as model-taxa-by-homoplasy for the early evolution of the Cryptocercus+Isoptera clade, as their brooding behavior is more elaborate than in P. boleiriana.     

The evolutionary transition from subsocial to eusocial behaviour in Dictyoptera: phylogenetic evidence for modification of the "shift-in-dependent-care" hypothesis with a new subsocial cockroach

Cockroaches have always been used to understand the first steps of social evolution in termites because they are close relatives with less complex and integrated social behaviour. Termites are all eusocial and ingroup comparative analysis would be useless to infer the origin of their social behaviour. The cockroach genus Cryptocercus was used as a so-called "prototermite" model because it shows key-attributes similar to the termites (except Termitidae): wood-feeding, intestinal flagellates and subsocial behaviour. In spite of these comparisons between this subsocial cockroach and eusocial termites, the early and remote origin of eusocial behaviour in termites is not well understood yet and the study of other relevant "prototermite" models is however needed. A molecular phylogenetic analysis was carried out to validate a new "prototermite" model, Parasphaeria boleiriana which shows a peculiar combination of these key-attributes. It shows that these attributes of Parasphaeria boleiriana have an independent origin from those of other wood-eating cockroaches and termites. The case of P. boleiriana suggests that a short brood care was selected for with life on an ephemeral wood resource, even with the need for transmission of flagellates. These new phylogenetic insights modify evolutionary hypotheses, contradicting the assumption made with Cryptocercus model that a long brood care is necessary for cooperation between broods in the "shift-in-dependent-care" hypothesis. An ephemeral wood resource is suggested to prompt generation overlap and the evolution of cooperation, even if brood care is shortened.     

Phylogenetic position of Lophomonas striata Bütschli (Parabasalia) from the hindgut of the cockroach Periplaneta americana

Lophomonas striata is a multiflagellate parabasalid commensal in the hindgut of the omnivorous cockroaches Blatta orientalis and Periplaneta americana. Its closest relatives were traditionally thought to include similar multiflagellate parabasalids with a single flagellar area that degenerates during mitosis, such as Joenia and Kofoidia. However, molecular phylogenetic analyses have shown that "lophomonads" are not monophyletic. We have determined the SSU rRNA sequence of L. striata and we find that it branches sister to the Trichonymphida with strong support. This is surprising because all other lophomonads sampled to date branch within the Cristamonadida, and the order Trichonymphida (e.g. Trichonympha, Pseudotrichonympha, and Hoplonympha) is both morphologically coherent and monophyletic in SSU rRNA phylogenies. Trichonymphida, unlike the lophomonads, share a bilateral symmetry, in which their multiple flagella occur in two (or sometimes four) regions, and instead of degenerating upon mitosis, half of the flagella are passed to each daughter cell. The single apical flagellar region characteristic of lophomonads is therefore either plesiomorphic or it has arisen multiple times in parabasalids; our phylogenetic analyses and available ultrastructural evidence suggest the latter. Our results also suggest that parabasalid gut symbionts may have been vertically transmitted in cockroaches before the common ancestor of Cryptocercus and termites.     

Cospeciation in the triplex symbiosis of termite gut protists (Pseudotrichonympha spp.), their hosts, and their bacterial endosymbionts

A number of cophylogenetic relationships between two organisms namely a host and a symbiont or parasite have been studied to date; however, organismal interactions in nature usually involve multiple members. Here, we investigated the cospeciation of a triplex symbiotic system comprising a hierarchy of three organisms -- termites of the family Rhinotermitidae, cellulolytic protists of the genus Pseudotrichonympha in the guts of these termites, and intracellular bacterial symbionts of the protists. The molecular phylogeny was inferred based on two mitochondrial genes for the termites and nuclear small-subunit rRNA genes for the protists and their endosymbionts, and these were compared. Although intestinal microorganisms are generally considered to have looser associations with the host than intracellular symbionts, the Pseudotrichonympha protists showed almost complete codivergence with the host termites, probably due to strict transmissions by proctodeal trophallaxis or coprophagy based on the social behaviour of the termites. Except for one case, the endosymbiotic bacteria of the protists formed a monophyletic lineage in the order Bacteroidales, and the branching pattern was almost identical to those of the protists and the termites. However, some non-codivergent evolutionary events were evident. The members of this triplex symbiotic system appear to have cospeciated during their evolution with minor exceptions; the evolutionary relationships were probably established by termite sociality and the complex microbial community in the gut.     

Evidence for cocladogenesis between diverse dictyopteran lineages and their intracellular endosymbionts

Bacteria of the genus Blattabacterium are intracellular symbionts that reside in specialized cells of cockroaches and the termite Mastotermes darwiniensis. They appear to be obligate mutualists, and are transmitted vertically in the eggs. Such characteristics are expected to lead to equivalent phylogenies for host and symbiont, and we tested this hypothesis using recently accumulated data on relationships among termites and cockroaches and their Blattabacterium spp. Host and symbiont topologies were found to be highly similar, and various tests indicated that they were not statistically different. A close relationship between endosymbionts from termites and members of the wood-feeding cockroach genus Cryptocercus was found, supporting the hypothesis that the former evolved from subsocial, wood-dwelling cockroaches. The majority of the Blattabacterium spp. sequences appear to have undergone similar rates of evolution since their divergence from a common ancestor, and an estimate of this rate was determined based on early Cretaceous host fossils. The results support the idea that the stem group of modern cockroaches radiated sometime between the late Jurassic and early Cretaceous-not the Carboniferous, as has been suggested on the basis of roach-like fossils from this epoch.     

A mitochondrial genome phylogeny of termites (Blattodea: Termitoidae): Robust support for interfamilial relationships and molecular synapomorphies define major clades

Despite their ecological significance as decomposers and their evolutionary significance as the most speciose eusocial insect group outside the Hymenoptera, termite (Blattodea: Termitoidae or Isoptera) evolutionary relationships have yet to be well resolved. Previous morphological and molecular analyses strongly conflict at the family level and are marked by poor support for backbone nodes. A mitochondrial (mt) genome phylogeny of termites was produced to test relationships between the recognised termite families, improve nodal support and test the phylogenetic utility of rare genomic changes found in the termite mt genome. Complete mt genomes were sequenced for 7 of the 9 extant termite families with additional representatives of each of the two most speciose families Rhinotermitidae (3 of 7 subfamilies) and Termitidae (3 of 8 subfamilies). The mt genome of the well supported sister-group of termites, the subsocial cockroach Cryptocercus, was also sequenced. A highly supported tree of termite relationships was produced by all analytical methods and data treatment approaches, however the relationship of the termites+Cryptocercus clade to other cockroach lineages was highly affected by the strong nucleotide compositional bias found in termites relative to other dictyopterans. The phylogeny supports previously proposed suprafamilial termite lineages, the Euisoptera and Neoisoptera, a later derived Kalotermitidae as sister group of the Neoisoptera and a monophyletic clade of dampwood (Stolotermitidae, Archotermopsidae) and harvester termites (Hodotermitidae). In contrast to previous termite phylogenetic studies, nodal supports were very high for family-level relationships within termites. Two rare genomic changes in the mt genome control region were found to be molecular synapomorphies for major clades. An elongated stem-loop structure defined the clade Polyphagidae + (Cryptocercus+termites), and a further series of compensatory base changes in this stem-loop is synapomorphic for the Neoisoptera. The complicated repeat structures first identified in Reticulitermes, composed of short (A-type) and long (B-type repeats) defines the clade Heterotermitinae+Termitidae, while the secondary loss of A-type repeats is synapomorphic for the non-macrotermitine Termitidae.     

Vertical transmission as the key to the colonization of Madagascar by fungus-growing termites?

The mutualism between fungus-growing termites (Macrotermitinae) and their mutualistic fungi (Termitomyces) began in Africa. The fungus-growing termites have secondarily colonized Madagascar and only a subset of the genera found in Africa is found on this isolated island. Successful long-distance colonization may have been severely constrained by the obligate interaction of the termites with fungal symbionts and the need to acquire these symbionts secondarily from the environment for most species (horizontal symbiont transmission). Consistent with this hypothesis, we show that all extant species of fungus-growing termites of Madagascar are the result of a single colonization event of termites belonging to one of the only two groups with vertical symbiont transmission, and we date this event at approximately 13 Mya (Middle/Upper Miocene). Vertical symbiont transmission may therefore have facilitated long-distance dispersal since both partners disperse together. In contrast to their termite hosts, the fungal symbionts have colonized Madagascar multiple times, suggesting that the presence of fungus-growing termites may have facilitated secondary colonizations of the symbiont. Our findings indicate that the absence of the right symbionts in a new environment can prevent long-distance dispersal of symbioses relying on horizontal symbiont acquisition.     

低等白蚁肠道共生微生物的多样性及其功能

低等白蚁肠道里存在着复杂的微生物区系,包括真核微生物鞭毛虫和原核生物,细菌及古细菌。低等白蚁的后肠以特别膨大的囊形胃及其氢氧浓度的明显梯度分布和丰富的微生物区系为特征,是白蚁进行木质纤维素消化的主要器官。后肠内的鞭毛虫能将纤维素水解并发酵为乙酸,二氧化碳和氢,为白蚁提供营养和能源。系统发育研究表明,低等白蚁肠道共生细菌的主要类群为白蚁菌群1、螺旋体、拟杆菌,低G C mol%含量的革兰氏阳性菌和紫细菌等。而古细菌主要为甲烷短杆菌属的产甲烷菌。共生原核生物与二氧化碳的还原和氮的循环等代谢有关。但肠道共生微生物的具体功能和作用机制还有待进一步的揭示。     

高效降解木质纤维素的白蚁肠道微生物组

木食性白蚁是自然界木质纤维素的高效降解者,在长期进化过程中白蚁与其肠道微生物组协同作用发展出不同的纤维素降解机制。木食性白蚁具有分别来源于白蚁和共生微生物的两套纤维素酶系统。在低等白蚁中,木质颗粒经过白蚁前、中肠分泌的内源性酶初步消化后,在后肠共生鞭毛虫中被降解为乙酸、二氧化碳和氢。高等木食性白蚁在进化中丢失了鞭毛虫,木质颗粒经白蚁自身分泌的酶初步消化后,在后肠大量共生细菌的帮助下被有效降解。培菌类白蚁利用其菌圃中的蚁巢伞菌和肠道微生物协同作用降解木质纤维素。共生微生物在白蚁的氮素固定与循环、中间产物代谢及纤维素降解等过程中发挥了重要作用。学习和模拟白蚁高效降解木质纤维素的体系,对生物质能源的产业化发展具有积极的意义。     

A case for ancestral transfer of symbionts between cockroaches and termites

Living species of the cockroach family Cryptocercidae have intestinal symbionts that are congeneric with some of the gut protozoa found in Isoptera. Presence of such closely related symbionts in cryptocercids and in termites has been frequently interpreted as a uniquely derived homologous character shared between the two xylophagous groups. This may not be the most parsimonious interpretation. Cryptocercus nymphs placed into Zootermopsis (dampwood termite) colonies were killed and eaten by the termites. Termites placed into a Cryptocercus nest box were also fully consumed. Modern Cryptocercus punctulatus and Zootermopsis are often found in the same decaying logs in the Pacific Northwest of the U.S.A., and it is likely that their ancestors also cohabited in at least a portion of their ranges. By occasionally killing and consuming an intruder from the other group, gut protozoa could have been acquired and exchanged between termites and Cryptocercus or their ancestors, under natural conditions and before the life histories of the protozoa became specialized within the host orders. Implications for assessing the phylogeny of the two dictyopteroid groups are also discussed.     

Purine biosynthesis-deficient Burkholderia mutants are incapable of symbiotic accommodation in the stinkbug

The Riptortus–Burkholderia symbiotic system represents a promising experimental model to study the molecular mechanisms involved in insect–bacterium symbiosis due to the availability of genetically manipulated Burkholderia symbiont. Using transposon mutagenesis screening, we found a symbiosis-deficient mutant that was able to colonize the host insect but failed to induce normal development of host''s symbiotic organ. The disrupted gene was identified as purL involved in purine biosynthesis. In vitro growth impairment of the purL mutant and its growth dependency on adenine and adenosine confirmed the functional disruption of the purine synthesis gene. The purL mutant also showed defects in biofilm formation, and this defect was not rescued by supplementation of purine derivatives. When inoculated to host insects, the purL mutant was initially able to colonize the symbiotic organ but failed to attain a normal infection density. The low level of infection density of the purL mutant attenuated the development of the host''s symbiotic organ at early instar stages and reduced the host''s fitness throughout the nymphal stages. Another symbiont mutant-deficient in a purine biosynthesis gene, purM, showed phenotypes similar to those of the purL mutant both in vitro and in vivo, confirming that the purL phenotypes are due to disrupted purine biosynthesis. These results demonstrate that the purine biosynthesis genes of the Burkholderia symbiont are critical for the successful accommodation of symbiont within the host, thereby facilitating the development of the host''s symbiotic organ and enhancing the host''s fitness values.     

Lignocellulose degradation by microorganisms from termite hills and termite guts: A survey on the present state of art

Abstract: In several aspects termites are a fascinating group of insects having attracted the interest of many researchers. They exhibit a complex social behavior and caste differentiation occurring elsewhere only among the hymenoptera. In an enlarged part of the hindgut, the paunch, termites have established a unique symbiotic association with prokaryotic and eukaryotic microorganisms. A similar flora is also found in wood-eating roaches of the genus Cryptocercus . The study of symbiosis between termites and their intestinal microbes is of general interest, because due to this symbiotic interaction termites can feed on complex biopolymers such as wood. Flagellates and bacteria occur in the gut of lower termites, while higher termites possess only bacteria. In particular spirochetes are abundant in the termite gut. Apart from spirochetes and other more common bacteria, actinomycetes, yeasts and fungi have also been isolated from different species of termites. This review summarizes the distinct role of the intestinal flora in degradation of wood components such as cellulose, hemicellulose and lignin.