Coptotermes formosanus is a well-known wood-feeding termite that can degrade lignocellulose polysaccharides efficiently with its unique multi-enzyme catalysis system. β-glucosidase (BG) is one of the important cellulases in its enzyme system. However, there may present multiple endogenous BGs in termite digestive system for various properties and functions. This study aims to characterize two BG homologs and reveal their potential coordinative effect. In this study, two endogenous BG homologs (CfGlu1B and CfGlu1C) from C. formosanus showed different substrate specificity. CfGlu1B favors cellobiose while CfGlu1C favors sucrose. Besides, CfGlu1C exhibited higher alkali resistance than CfGlu1B. Kinetic analysis revealed that CfGlu1B enzyme’s activity toward p -NP-β-D-glucopyranoside ( p -NPG) was higher than that of CfGlu1C, and the difference mainly attributes to the turnover number ( K
cat ). In addition, the activity assay showed significant synergistic action of CfGlu1B and CfGlu1C in degrading D-lactosum. For effect of metals, Cu 2+ inhibited both enzymes and Ca 2+ increased the activity of CfGlu1C but not CfGlu1B. Site-directed mutagenesis analysis indicated that both enzymes lost activities when residues E190 of CfGlu1B and E168 of CfGlu1C were mutated to alanine, respectively, which were essential active centers of the GHF1 enzymes. Moreover, mutation H252N increased the activity of enzyme CfGlu1C by 2.1-fold. This study implies interesting possibilities for better practical biotechnological use in green energy production.
Wenhui Zeng,Bingrong Liu,Wenjing Wu,Shijun Zhang,Yong Chen,Zhiqiang Li
Simple SummaryCoptotermes formosanusShiraki is a wood feeding lower termite and is widely distributed in many areas. The dynamic adjustment of theC. formosanusdigestive system to unfavorable survival environments was investigated via non-lethal toxic feeding. The toxic stress did not change the dominant role of microbial lignocellulases in cellulose degradation ofC. formosanus. The core symbiotic community was stable in abundance during the tolerance to the toxic treatment. However, a large number of low abundance taxa were significantly enriched by the low toxic feeding. These rare bacterial lineages likely contribute to toxic stress tolerance of termite. Above all, these findings add important new knowledge to our understanding of environmental adaptation of the lignocellulose hydrolysis system in termites.AbstractDisturbing the lignocellulose digestive system of termites is considered to be a promising approach for termite control. The research on the tolerance mechanism of the termite lignocellulose digestive system to harmful environment conditions is limited. In this study, we keepCoptotermes formosanusSkiraki under a non-lethal toxic condition by feeding the termites with filter paper containing the kojic acid (a low toxic insecticide). The effects of low toxic stress on the activities and gene expressions of host/symbiotic originated lignocellulases, and on the symbiotic microbial community structure ofC. formosanuswere explored. Our result showed that the low toxic stress would lead to the synchronous decrease of cellulase and hemicellulase activities, and supplementary increase of corresponding gene expressions. The symbiotic community maintained its role as the main force in the lignocellulolytic system ofC. formosanus. Meanwhile, a large number of rare taxa were significantly enriched by kojic acid treatment. These numerically inconspicuous bacterial populations might be responsible for the functions similar to phenoloxidase or insecticide detoxification and enableC. formosanusto tolerate the harmful environment. Overall, our data suggested that the digestive adaptation ofC. formosanusto physiotoxic feeding is closely related to the triple collaboration of termites–flagellates–bacteria.Keywords:lignocellulolytic system;non-lethal stress;symbiont;termite;toxic tolerance
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