Effects of Pichia anomala and cellulase on methane production potential of sweet sorghum silage

The effects of Pichia anomala, cellulase, and a combination of both on the regulation of ensiling quality and methanogenic potential during anaerobic digestion of sweet sorghum were investigated in this study. Moreover, microbial community diversity during anaerobic digestion was analyzed using high-throughput DNA sequencing, and economic performance was evaluated to screen for inexpensive and highly efficient additives. The results revealed that the two additives improved the ensiling fermentation quality of sweet sorghum to different extents. The highest comprehensive assessment value was for the silages treated with the combination of P. anomala and cellulase (PC, 0.66), followed by 0.63 in silages treated with P. anomala alone (Pa). PC was effective in preserving energy components such as water-soluble carbohydrates, crude protein, cellulose, and hemicellulose in sweet sorghum silage. The addition of the two could also reduce lignocellulosic components, such as acid detergent lignin, neutral detergent fiber, and acid detergent fiber and subsequently increase the content of lactic and acetic acid and enhance ensiling fermentation. In particular, there were more residual water-soluble carbohydrates and the highest lignin removal (62.55%) after PC treatment, and the well-preserved protein and the highest lactic and acetic acid content, 50.01 g·kg⁻¹ and 18.35 g·kg⁻¹ (based on dry matter, DM), were determined in Pa silages. Ensiling pretreatment markedly improved the methanogenic potential of sweet sorghum. In particular, for PC, the maximum cumulative methane production was 457.70 mL(CH₄)·g⁻¹ (based on volatile solids, VS), which was increased by 30.13% compared to raw sweet sorghum, the maximum biodegradability index was 72.39%, and the lag phase was decreased by 62.96% compared to raw sweet sorghum (CK). In comparison with CK, the maximum methane production rate in Pa increased by 33.57%, and the lag phase decreased by 33.33%. The species richness of bacteria and archaea increased after sweet sorghum was treated with additives. Simultaneously, the use of different silage additives can affect the variation in bacterial community diversity with fermentation time but no such effect was observed in archaea. At the genus level, the dominant bacteria in the anaerobic digestion effluent were Fermentimonas and Clostridium_ sensu_stricto_1, which negatively correlated with pH and positively correlated with chemical oxygen demand (COD) and total volatile fatty acid (TVFA). The dominant archaea were Methanosarcina and Methanobrevibacter, where Methanosarcina was negatively correlated with COD and TVFA and positively correlated with pH. Methanobrevibacter was positively correlated with COD and TVFA concentrations and negatively correlated with pH. After the combined analysis of ensiling quality, methanogenic performance, and economy, it is recommended to use Pa as a biological additive for ensiling pretreatment in practical production.