| The energy crisis and environmental pollution has been serious global problems for a long time, and the development of alternative biomass energy is considered to be one of the most effective ways. In recent years, the idea of bionic use of termite, one of the most efficient lignocellulose conversion systems in nature, is widely concerned. Higher termites of the subfamily Macrotermitinae, which is also called fungus-growing termites, can specifically cultivate basidiomycetes fungi (Termitomyces Spp.) in their nest. In this thesis, the most widely distributed and harmful fungus-growing termites(Odontotermes formosanus Shiraki) is taken as an object of study. And comprehensive research tools including biological behavior, digestive physiology, plant fiber chemistry and microbial ecology, were applied so as to investigate the digestive strategy of O. formosanus on lignocellulosic materials. Specifically, include the followings:(1) With the developed visible artificial rearing system for O. formosanus, we artificially reared several nests of O. formosanus sampled from the wild field for a long time for video observation. And obvious division of labor in the process of lignocellulosic food recycling was observed. Briefly, older adult worker termites forage and bring food back to the nest; then young adult workers ingested the collected food as well as the fungus nodules composed of asexual spores on the fungus garden, and extrude primary feces as new fungus garden; old adult termites feed on the mature garden after fully fermented.(2) Through the in situ detection of the physical morphology and chemical structure of the lignocellulose particles within the digestive system of O. formosanus. Firstly, it showed that with the help of the symbiotic fungus, no significant changes in the physical form of lignocellulose particles was observed in O. formosanus, thus the lignin barrier can not be effectively opened. Secondly, with the help of the symbiotic microorganisms on the fungus garden, significant spatial and temporal degradation process of lignocellulose was observed in the upper, middle and lower garden. That the side chains of the S-type lignin may be selectively oxidized first, resulting in lignin depolymerization, followed by the ring-opening reaction of lignin monomer and the disappearance of a large group of lignin monomers, leaving large amounts of polysaccharide in the final pretreated lignocellulosic substrate.(3) Through microscopy techniques such as microelectrodes and ICP-MS, physicochemical microenvironment profiles of the digestive system of O. formosanus including oxygen, pH, redox potential, hydrogen and metal ion concentration were revealed. The intestinal system of O. formosanus shows a relatively low oxygen partial pressure ranging from0to8.6kPa; neutral pH value (pH value6.1-7.4) distributed throughout different intestinal segments except the rectal area; average oxidation reduction potential in the central region of each section of the intestine (except rectum) were generally higher, between about70to310mV. In particular, as the intermediates of lignocellulose degradation, the hydrogen partial pressure went up to10.4kPa in the hindgut paunch. Furthermore, by ICP-MS, the concentration of13kinds of metal ions in the termite gut, fungus garden and the soil on the nest were measured, indicating that in the main area of the digestive tract,6out of13kinds of metal ions (potassium, magnesium, manganese, barium, selenium, molybdenum) showed significant differences in spatial distribution, a significant enrichment of certain metal ions were also observed in samples of the rectum, fungus garden and nest soil.(4) Through the high-throughput454pyro-sequencing, the16s rRNA genes of the bacteria residing in different ages and locations of O. formosanus were amplified and sequenced. Through bioinformatical analysis including taxonomic classification, OTU division and network structure, community structure of the sampled termite was investigated. It showed that significant temporal and spatial heterogeneity of the intestinal bacterial community exists. These results indicated that gut microbes residing in digestive track of O. formosanus showed obvious response to lignocellulosic substrates. |
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