Comparative genomic and secretomic characterisation of endophytic Bacillus velezensis LC1 producing bioethanol from bamboo lignocellulose

Abstract

Background: Compared to physical and chemical methods, microbial lignocellulosic degradation is a green process. Bacillus is an excellent organic matter degrader, and it has exhibited various abilities required for lignocellulose degradation, including the degradation of cellulose, hemicellulose and lignin. Several B. velezensis strains encode lignocellulosases. However, their usefulness based on their ability to transform biomass has not been appreciated. Genomic, comprehensive comparative genomic and secretomic analyses were used to clarify the lignocellulose-degrading potential of these bacteria, which is necessary for their future application.Results: In the present study, the complete genomes of 20 B. velezensis strains and an endophytic bacterium, B. velezensis LC1, were analysed to find common and unique genes encoding carbohydrate-active enzymes (CAZymes) and evaluate their potentials to degrade lignocellulose. By comparative whole genomic and CAZyomic analyses of all 21 strains, we identified genes of lignocellulolytic enzymes with the potential to degrade cellulose (GH5, GH30, GH4, GH1, GH16 and GH32) and hemicellulose (GH43, GH30, GH51, GH26 and GH53). Further identification of the secretome of B. velezensis LC1 by liquid chromatography-tandem mass spectrometry (LC-MS/MS) confirmed that a considerable number of proteins in the culture medium are involved in lignocellulose degradation, including endoglucanase, hemicellulases, and other related proteins. Moreover, assays of the activities of several lignocellulolytic enzymes including endoglucanase, exoglucanase, β-glucosidase, xylanase, lignin peroxidase, laccase, and manganese peroxidase show that these enzymes are more active in bamboo powder compared to glucose substrates. After a 6-day treatment, the degradation efficiencies of cellulose, hemicellulose and lignin from bamboo powder were 59.90%, 75.44% and 23.41%, respectively. The hydrolysate was subjected to ethanol fermentation with Saccharomyces cerevisiae and Escherichia coli KO11, yielding 10.44 g/L ethanol after 96 h.Conclusions: These findings indicate that Bacillus velezensis strains have the potential to degrade a range of polysaccharides in lignocellulosic biomass. One strain, B. velezensis LC1, efficiently degrades bamboo lignocellulose components, allowing for subsequent ethanol production.