Plant cell-wall polysaccharides constitute the most abundant but recalcitrant organic carbon source in nature. Microbes residing in the digestive tract of herbivorous bilaterians are particularly efficient at depolymerizing polysaccharides into fermentable sugars and play a significant support role towards their host’s lifestyle. Here, we combine large-scale functional screening of fosmid libraries, shotgun sequencing, and biochemical assays to interrogate the gut microbiota of the wood-feeding “higher” termite Globitermes brachycerastes. A number of putative polysaccharide utilization gene clusters were identified with multiple fibrolytic genes. Our large-scale functional screening of 50,000 fosmid clones resulted in 464 clones demonstrating plant polysaccharide-degrading activities, including 267 endoglucanase-, 24 exoglucanase-, 72 β-glucosidase-, and 101 endoxylanase-positive clones. We sequenced 173 functionally active clones and identified ~219 genes encoding putative carbohydrate-active enzymes (CAZymes) targeting cellulose, hemicellulose and pectin. Further analyses revealed that 68 of 154 contigs encode one or more CAZyme, which includes 35 examples of putative saccharolytic operons, suggesting that clustering of CAZymes is common in termite gut microbial inhabitants. Biochemical characterization of a representative xylanase cluster demonstrated that constituent enzymes exhibited complementary physicochemical properties and saccharolytic capabilities. Furthermore, diverse cellobiose-metabolizing enzymes include β-glucosidases, cellobiose phosphorylases, and phopho-6-β-glucosidases were identified and functionally verified, indicating that the termite gut micro-ecosystem utilizes diverse metabolic pathways to interconnect hydrolysis and central metabolism. Collectively, these results provide an in-depth view of the adaptation and digestive strategies employed by gut microbiota within this tiny-yet-efficient host-associated ecosystem.
|Number of pages||14|
|State||Published - Jan 1 2019|
Bibliographical noteFunding Information:
Acknowledgements We thank J. Thompson from National Institute of Dental and Craniofacial Research, NIH and C. Zhou from University of Science and Technology of China for providing cellobiose-6-phosphate substrate for 6-phospho-β-glucosidase activity assay, D.J. Yelle from US Forest Products Laboratory for the comments of plant cell structure, DeepBiome Co., Ltd. for bioinformatic assistance. This work was founded by the National Natural Science Foundation of China (31472046 and 31172153) for QW. Funding for CRC and HL was provided by the Department of Energy Great Lakes Bioenergy Research Center Office of Science Grant DE-FC02-07ER64494. MGC was supported by National Institutes of Health National Research Service Award T32 GM008505. PBP is supported from The Research Council of Norway’s FRIPRO program (250479), as well as the European Research Council Starting Grant Fellowship (336355 - MicroDE).
© 2018, International Society for Microbial Ecology.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics