Whole-Genome Sequencing Reveals Lignin-Degrading Capacity of a Ligninolytic Bacterium (Bacillus cereus) from Buffalo (Bubalus bubalis) Rumen

The buffalo is an amazing ruminant. Its ability to degrade lignin, which has been recently reported, is most likely due to unique rumen microorganisms with lignin-degradation potential. Our goal was to explore the lignin-degradation potential of ruminal microorganisms, in which ligninolytic enzyme encoding genes were involved to provide ideas for revealing the mechanism of lignin degradation by buffalo. In this study, a bacterium strain identified as Bacillus cereus AH7-7 was isolated from the buffalo (Bubalus bubalis) rumen. After whole-genome sequencing, the results demonstrated that B. cereus AH7-7 had laccase, cytochrome P450 and vanillin alcohol oxidase-encoding genes. Sixty-four genes of B. cereus AH7-7 were involved in multiple aromatic metabolic pathways, such as phenylalanine metabolism and aminobenzoate degradation. A positive reaction resulting in guaiacol medium indicated that laccase secretion from B. cereus AH7-7 increased with time. A biodegradation experiment revealed that a significant reduction in kraft lignin content (25.9%) by B. cereus AH7-7 occurred at the end of 6 days of incubation, which confirmed its lignin-degradation capacity. Overall, this is the first report showing that B. cereus AH7-7 from the buffalo rumen can degrade lignin, and revealing the encoding genes of lignin-degrading enzymes from genome level.