The water buffalo (Bubalus bubalis) is known for its unique utilization of low-quality fibrous feeds and outstanding digestion performance, highlighting its role as an animal model in studying fiber fractions degradation. Among roughage, lignin attracted wide attention in ruminant nutrition studies, which affects animal digestibility. Therefore, the present study aims to investigate the functional relation between three lignin monomeric compositions of coniferyl alcohol (G), ρ-coumaryl alcohol (H) and sinapyl alcohol (S) and ruminal fiber degradation in water buffalo. Hence, three female water buffaloes (Nili-Ravi × Mediterranean, five years old, 480 ± 20 kg) were assigned for an in vivo study by utilizing the nylon-bag method, examining eight kinds of roughage. All the experimental roughage types were analyzed for the effective degradability (ED) of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), cellulose (CEL) and hemicellulose (HC) fractions. Then, prediction models for the roughage fiber degradation were established based on the characteristics of lignin monomer content. The results showed that S, S/G and S/(G+S+H) were positively correlated with the ED of NDF, ADF, CEL and HC; H/S was negatively correlated. For the effective degradability of ADL (ADLD), S and S/(G+S+H) were positively correlated with it; H, H/G, H/S and H/(G+S+H) were negatively correlated. The model with the highest fitting degree was ADLD = 0.161 − 1.918 × H + 3.152 × S (R² = 0.758, p < 0.01). These results indicated that the lignin monomer composition is closely related to the utilization rate of roughage fiber. S-type lignin monomer plays a vital role in the fiber degradation of roughage. The experiment found the effect of lignin monomer composition on the degradation of fiber fractions using buffalo as the experimental animal and constructed prediction models, providing a scientific basis for building a new technological method using lignin composition to evaluate buffalo roughage. Furthermore, the capacity of ADL degradation of buffalo was proved in this experiment. In order to further explore the ability of lignin degradation by the buffalo, the DNA of rumen microorganisms was extracted for sequencing. The top three composition of rumen microorganisms at the genus level were Prevotella_1, 226, Rikenellaceae_RC9_gut_group and Ruminococcaceae_UCG-011. Six strains with lignin degradation ability were screened from buffalo rumen contents. This experiment also revealed that the buffalos possess rumen microorganisms with lignin degradation potential.

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.