Whole-Genome Analysis and Lignin Degradation Characterization of Termite-Derived Bacillus cereus BC-8

Lignin is one of the primary biomass resources in nature; however, its highly stable structure makes it difficult to degrade and utilise. As efficient decomposers of lignocellulosic biomass, termites rely on their gut microbiota for digestion. Consequently, termite guts harbour abundant and specialized lignin-degrading microorganisms. In this study, we isolated a bacterium from the termite gut and identified it as Bacillus cereus BC-8. The laccase activity of B. cereus BC-8 reached the maximum of 87.8 U/L at 72 h, and the lignin degradation rate reached 33.66% within 7 days. Furthermore, we analyzed the structural changes in lignin after treatment with this bacterial strain. Field emission scanning electron microscopy observations revealed that the surface structural integrity of lignin was significantly disrupted after treatment. Fourier transform infrared spectroscopy analysis indicated that B. cereus BC-8 affected the side chains and aromatic skeleton structures of lignin. Thermogravimetric analysis further revealed that B. cereus BC-8 disrupted the primary inter-unit β-O-4 ether bonds of lignin. Whole-genome sequencing of B. cereus BC-8 revealed a genome length of 5,374,773 bp and a GC content of 35.34%. Functional gene annotation revealed that the B. cereus BC-8 genome contains genes encoding various lignin-degrading enzymes (laccase, cytochrome P450, and vanillin oxidase) and their auxiliary factors, along with the phenylalanine and benzoic acid metabolic pathways, which are associated with lignin degradation. In conclusion, B. cereus BC-8 can break down the side chains, aromatic skeletons, and β-O-4 ether bonds of lignin molecules, demonstrating excellent lignin degradation ability. At the molecular level, this study elucidates the key genes and metabolic pathways related to lignin degradation in the genome of B. cereus BC-8.