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

Abstract

Bacillus is an excellent organic matter degrader, and it has exhibited various abilities required for lignocellulose degradation. Several B. velezensis strains encode lignocellulosases and however their usefulness based on their ability to transform biomass has not been appreciated. In the present study, genomic, comprehensive comparative genomic and secretomic analyses were used to clarify the lignocellulose-degrading potential of these bacteria. The complete genomes of 20 B. velezensis strains and an endophytic strain, 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 coding for lignocellulolytic enzymes with the potential to degrade cellulose and hemicellulose. 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 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. These findings indicate that B. velezensis LC1, efficiently degrades bamboo lignocellulose components, allowing for subsequent ethanol production.