| Termites are one of the five most important pests studied by the international research of ecology. Owing to the numerous species and widespread food resources, termites cause a tremendous amount of economic damage to the society. Billions of dollars are lost in the world every year because of termites.It has been shown that the symbiotic gut microbiota in wood-feeding lower termites plays an important role in the digestion of different plant components. However, till recently, very little was known about how the gut microbiota is involved in digestion.To obtain a better understanding of the microbiota inhabiting the intestinal tract of wood-feeding lower termites, the European subterranean termite, Reticulitermes santonensis (Feytaud) (Isoptera: Rhinotermitidae), was used as a model system. The diversity and structure of the bacterial community in the different niches of the gut, as well as the distribution and location of major bacterial phylotypes within the intestinal tract was evaluated using various molecular techniques such as clonal analysis, DNA fingerprinting, and fluorescence in situ hybridization. In addition, the symbiotic bacteria associated with the flagellate, Pyrsonympha vertens in the gut of the closely related Eastern subterranean termite, Reticulitermes flavipes (Kollar), were phylogenetically characterized. AH of the results were reported for the first time in the world, which form the basis for further studies on the metabolic mechanisms of the gut microbiota, and for the new strategies to control wood-feeding lower termites by moving out the symbiotic microorganisms. The main results of this study are as follows:1. This was the first report on the phylogenetic characterization of the symbiotic bacteria associated with the symbiotic flagellate Pyrsonympha vertens in the gut of Reticulitermes flavipes. Single cells of P. vertens were isolated from diluted gut fluid of this termite with the aid of a micromanipulator. A clone library of the 16S rRNA genes of the bacteria associated with P. vertens was established. Clones were sorted based on the restriction fragment length polymorphism (RFLP) analysis, and the almost complete 16S rRNA genes of five clones were sequenced. Four of these clones were affiliated with the so-called Termite group 1 (TG-1) phylum, and one clone was affiliated with the Cytophaga-Flexibacter-Bacteroides (CFB) phylum. The ratio of the clone frequencies of the two phylotypes revealed that bacteria affiliated with these two phyla were dominant in P. vertens.2. The bacterial microbiota in the four major intestinal habitats of Reticulitermes santonensis - the midgut, the wall of the hindgut paunch, the hindgut fluid, and the intestinal protozoa - were characterized by cloning and sequence analysis and by molecular fingerprinting (terminal restriction fragment length polymorphism; T-RFLP). The community comprised representatives of several phyla, including gram-positive bacteria (mainly clostridia, streptococci, and Mycoplasmatales-related clones), members of the CFB phylum, spirochetes, and a number of proteobacteria, all of which were unevenly distributed among the four fractions. The largest group of clones fell into the so-called TG-1 phylum, which has no cultivated representatives. The majorityof the TG-1 clones was associated with the protozoa and formed two phylogenetically distinct clusters, which consisted exclusively of clones previously retrieved from the gut of this and other Reticulitermes species. Also the other clones represented lineages of microorganisms that were exclusively recovered from the intestinal tract of termites. The termite specificity of these lineages was underscored by the finding that the closest relatives of the bacterial clones obtained from R. santonensis were usually derived also from the most-closely related termites, supporting the concept of co-evolution between gut microbiota and host. This study provides conclusive evidence that the diversity of the gut microbial community reflects niche heterogeneity in...
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