Valorisation of wheat straw and bioethanol production by a novel xylanase- and cellulase-producing Streptomyces strain isolated from the wood-feeding termite, Microcerotermes species

Abstract Lignocellulosic biomass represents an unlimited and ubiquitous energy source, effectively addressing current global energy demand challenges. However, the recalcitrant nature of lignocellulose hinders microbial degradation, necessitating an appropriate hydrolytic enzyme production source for biomass valorisation and bioethanol production. This study might be the first to explore a novel bacterial species Streptomyces sp. strain MS-S2, isolated from the higher wood-feeding termite, Microcerotermes sp.; capable of concurrent degradation and saccharification of wheat straw for the liberation of reducing sugars, which can further be converted to bioethanol. The Streptomyces sp. MS-S2 demonstrated the capacity to efficiently utilise wheat straw as the sole carbon source for the secretion of xylanase and cellulase enzymes. The highest cellulase and xylanase productions were observed for ten days when the bacterium was cultured in the medium amended with 15 g/L of wheat straw and 1.5% yeast extract at pH 8.0, 30 ℃. Under optimum conditions, xylanase and cellulase activities were estimated to be 6.560 ± 0.160 and 0.866 ± 0.067 U/mL, respectively. Through Scanning electron microscopy analysis, the surface accessibility of cellulose fibrils in treated wheat straw was observed, indicating the efficiency of the hydrolysis process. In addition, functional group modifications from Fourier transform infrared spectroscopy analysis demonstrated the successful depolymerisation of wheat straw. Further, excreted enzymes produced under optimal conditions were applied to wheat straw hydrolysis for the liberation of reducing sugars. Then, ethanol production was obtained at a maximum concentration of 10.8 g/L. The findings of this study could open a new path for the search of new lignocellulolytic-producing bacteria inhabiting the gut symbionts of wood-feeding termites to valorise lignocellulosic biomass into biotechnologically value-added products such as biofuels.