Isolation Of Cellulose-degrading Bacteria From Wood-feeding Higher Termites And The Analysis Of The Cellulase And Xylanase Activities Of These Bacteria

Termite is a well-known symbiotic system. The symbiotic association between termites and their gut microbiota is critical for termites for the degradation and turnover of lignocellulose. There are no symbiotic protozoa in wood-feeding higher termites. Therefore, it was assumed that the symbiotic bacteria in the gut of wood-feeding higher termites play important roles in cellulose degradation. However, so far, it is not clear how these bacteria affect the degrading process. In this study, we isolated cellulose-degrading bacteria from two wood-feeding higher termites, Nasutitermes sp. and Microcerotermes sp. and analyzed the cellulase and xylanase activities of these isolates. The results will be useful for the illustration of the symbiotic association between gut microbiota and wood-feeding higher termites, and forms the basis for further application of these microbial resources in biofuel industry. The main results of this study are as follows:1. A bacterial consortium was isolated from the gut of Nasutitermes sp. using filter paper as carbon sourceunder aerobic condition at37℃and pH7.2. This consortium can degrade filter paper after6days of inoculation stablely in continuous sub-culturings. The scanning electron microscopy showed that coccoi-like bacteria and rod shape bacteria were present in the consortium. DNS method was used to analyze the filter paper cellulase activity (1.06±0.01U/ml), endoglucanase activity (1.3U/ml), β-1,4-glucosidase activity (1.02±0.01U/ml) and xylanase activity (2.43±0.04U/ml). Producing conditions of these enzymes in the culturing product of the bacterial consortium were studied preliminarily. The analysis of the16S rDNA showed that there were two kinds of bacteria in this consortium, which belonged to serratia marcescens and paenibacillus kobensis and were named as NS1and NP1, respectively. Both NS1and NP1were successfully isolated from the consortium. The filter paper could not be degraded either by the sole culture of NS1or NP1. However, it can be degraded by co-culturing of NS1and NP1, which indicated that the two bacteria may have synergistic effects in cellulose degrading.2. Using a medium containing carboxymethylcellulose (CMC-Na) or xylan as the sole carbon source, two bacterial strains were isolated from the gut of Nasutitermes sp.and Microcerotermes sp., respectively. Both strains presented endoglucanase and xylanase activities on gongo red agar platesand were named as XB-7and JH-8, respectively. Strain XB-7had the highest similarity of99%with16S rDNA of Bacillus amyloyticus, whereas strain JH-8showed the highest similarity of99%with16S rDNA of Bacillus subtilis. The analysis of enzyme activities of liquid culture showed that strain XB-7had the highest endoglucanase(1.32±0.03U/ml) and xylanase activity(6.79±0.05U/ml) after3days’ and2days’ inocolation, respectively, whereas strain JH-8had the highest endoglucanase (3.60±0.25U/ml)and xylanase activity (5.09±0.32U/ml)after3days’ inocolation.