Localization of Symbiotic Clostridia in the Mixed Segment of the Termite Nasutitermes takasagoensis (Shiraki)

Abstract

Phylogeny and the distribution of symbiotic bacteria in the mixed segment of the wood-eating termite Nasutitermes takasagoensis (Shiraki) were studied. Bacterial 16S rRNA genes (rDNA) were amplified from the mixed segment of the gut by PCR, and two kinds of sequences were identified. The phylogenetic tree was constructed by neighbor-joining and maximum parsimony methods to identify symbionts harbored in the mixed segment. They are classified as low-G؉C-content gram-positive bacteria and are most closely related to the genus Clostridium. The distribution of these bacteria throughout the whole gut was examined by PCR using specific primers, which suggested that they are confined to the mixed segment despite the presence of bacteria throughout the gut. In situ hybridization indicated that the symbiotic bacteria were localized to the ectoperitrophic space between the midgut wall and the peritrophic membrane in the mixed segment. Electron microscopy revealed the close association between these bacteria and the mesenteric epithelium, suggesting that they have some interactions with the gut tissue of termites.It is widely known that termites cannot survive without intestinal microorganisms. The physiological functions of symbiotic prokaryotes in termites are extremely diverse and include cellulose digestion (21, 40), hemicellulose digestion (43, 47), acetogenesis (5, 29, 34), hydrogenesis (46, 47), methanogenesis (5, 35), sulfate reduction (28), and nitrogen fixation (39, 48). Moreover, intestinal bacteria contribute to creating suitable conditions for symbiotic flagellates through the production of nutrients and the maintenance of the pH and anaerobic conditions in "lower termites" (7). Such microorganisms are usually distributed in the enlarged part of the hindgut, called "the paunch"; metabolites from the microorganisms are considered to be absorbed across the hindgut wall (23). It has also been reported that termites belonging to the Termitidae, which do not have symbiotic protozoa and are known as "higher termites," possess bacteria not only in the hindgut but also in the mixed segment (1, 12).The mixed segment is a part of the gut present only in higher termites, where it is situated between the midgut and the first proctodeal segment (2). The basic structure of the mixed segment is such that the mesenteric epithelium occupies half of the gut wall and the proctodeal epithelium covers the remaining area. Though the role of the mixed segment is still ambiguous, some physiological characteristics have recently been clarified. One of the most significant features in the mixed segment is an elevated pH (3,7,8). In the case of the woodeating higher termite Nasutitermes nigriceps, a neutral pH value in the midgut increases in the mixed segment and reaches 10.23 Ϯ 0.46 in the first proctodeal segment (7). In contrast, oxygen concentration decreases in the mixed segment and becomes zero in the first proctodeal segment (7). Bacteria have been observed under such conditions in the ectoperitrophic space of the mixed segment,...

Phylogenetic Diversity, Abundance, and Axial Distribution of Bacteria in the Intestinal Tract of Two Soil-Feeding Termites ( Cubitermes spp.)

“…Another large cluster of 11 clones was affiliated with Clostridium piliforme and clostridial clones which have been localized in the alkaline mixed segment of the termite Nasutitermes takasagoensis (72). Although clustering was supported by all phylogenetic analyses, the low bootstrap value (60%) indicates that the exact branching order may change when additional sequences become available.…”

“…Considering the volume differences between the midgut and P1 segment (Table 1) and the strong drop in cell density between these segments (Table 2), the largest number of these organisms is apparently present in the midgut section, which comprises the alkaline mixed segment. Tokuda et al observed that the mixed segment of Nasutitermes takasagoensis, a woodfeeding higher termite, contains an apparently specific population of clostridia located between the midgut epithelium and the peritrophic membrane (72). Interestingly, the clonal isolates obtained in their study, NT-1 and NT-2, are not closely related to the clones in the P1 cluster but to many other clones recovered from the P1 of C. orthognathus, affiliated with cluster XIVb (Fig.…”

Intra- and Interspecific Comparisons of Bacterial Diversity and Community Structure Support Coevolution of Gut Microbiota and Termite Host

“…Several phylotypes from species M1 and M2 were clustered with clones obtained from the highly alkaline gut regions of higher termites. NT-1 and NT-2 were obtained from the mixed gut segment of Nasutitermes takasagoensis (49). Clones M-P1-, Pl-P1-, Tc-P1-, and S-P1-were obtained from the P1 gut segment of Microcerotermes sp., Pericapritermes latignathus, Termes comis, and Speculitermes sp., respectively (47).…”

High-Resolution Analysis of Gut Environment and Bacterial Microbiota Reveals Functional Compartmentation of the Gut in Wood-Feeding Higher Termites (Nasutitermes spp.)

“…(subfamily Termitinae) are colonized by different communities of bacteria and archaea (21,61), and the alkaline P1 compartments of different higher termites harbor a similar bacterial microbiota (68). However, apart from a study of the bacteria colonizing the mixed segment of Nasutitermes takasagoensis (subfamily Nasutitermitinae) (71), information about the microbial communities in the different hindgut sections of wood-feeding higher termites and a highly resolved analysis of important physicochemical parameters in the different gut regions are lacking.…”