Valorization of corn stover and molasses for enzyme synthesis, lignocellulosic hydrolysis and bioethanol production by Hymenobacter sp. CKS3

Abstract

During the last few decades, energy demand is increasing rapidly. Concerning this, the use of renewables - lignocellulose biomass, for bioethanol production, as an efficient alternative to replacing fossil fuels, is highly recommended. In this study, valorization of two agricultural wastes was used for various hydrolytic enzyme production by Hymenobacter sp. CKS3, lignocellulosic hydrolysis, and bioethanol production. Conditions for obtaining maximum enzyme production, using agro-industrial waste - molasses and corn stover, were statistically optimized. Under the optimal conditions, in a medium containing 5.0% corn stover, 2.5% molasses, and during 94.55 h (similar to 4 days) of fermentation, the maximum enzymatic activity was achieved - CMCase 1.11 IU/ml, Avicelase 0.92 IU/ml, and pectinase 3.69 IU/ml. The obtained crude enzyme mixture was further used for enzymatic hydrolysis of non-treated corn stover and bioethanol production. The reducing sugar yield of 3.85 g/l was obtained under optimal conditions (corn stover 6.6% and time of hydrolysis 78.8 h (similar to 3 days and 7 h)). Scanning electron microscopy revealed structural changes in corn stover samples after enzymatic hydrolysis. Under non-optimized conditions, 0.37% of ethanol was produced by waste brewer's yeast. The obtained results show that bacteria belonging to the genus Hymenobacter have a still unexplored enzymatic potential that could be used for sustainable production of biotechnologically value-added products including biofuels. Specifically, for the first time, a soil bacterium, classified within the genus Hymenobacter, was used for cellulases (CMCase and Avicelase) and pectinase production.