Functional annotation of carbohydrate binding modules of a termite gut symbiont Paenibacillus polymyxa

Agricultural and forestry waste available abundantly in the form of lignocellulosic biomass is considered a viable feedstock for production of second-generation biofuels. However, highly crystalline nature of biomass makes it recalcitrant towards enzyme digestion and fermentable sugar extraction.  Insects living on woody biomass have found a way to digest these biomasses by acquiring cellulase and hemicellulase producing microbial flora in their gut. We have sequenced the genome of the gut cellulolytic microbe P. polymyxa A18 and analyzed its genome for carbohydrate active enzymes (CAZymes). Its genome encoded 293 potential CAZymes which was higher than other well-known cellulolytic bacteria. We studied expression of CBM encoding polypeptides associated with catalytic domains of various CAZymes and found a distinct change in expression level of all CBM encoding polypeptides in response to soluble and insoluble sugars. CBMs highly induced in response to microcrystalline cellulose and biomass was able to enhance several fold activity of the catalytic domains of native or recombinant cellulases fused with it towards the crystalline substrate. Our study reveals the importance of gut microbes in hydrolysis of plant biomass with CBMs playing central role in substrate recognition.