Potential of enriched and stabilized anaerobic lignocellulolytic fungi coexisting with bacteria and methanogens for enhanced methane production from rice straw

Anaerobic lignocellulosic microbial consortia are known to be prodigiously efficient at converting lignocellulosic biomass to methane. In this study, the efficacy of anaerobic fungal consortia (AFC) from five different inocula, including Bubalus bubalis rumen fluid (RU), in degrading filter paper, microcrystalline cellulose, and rice straw (RS), was screened. The AFC from RU performed best in lignocellulosic material degradation and methane production; thus, RU was selected for further experiments. Consecutive batch subculturing (CBS) was performed in RU to enrich and stabilize the dominant and key microorganisms categorized as anaerobic fungi, using the addition of antibacterial agents to suppress the growth of untargeted bacteria. After the CBS, subculture E19 proved the most efficient, with RS degradation of 84% and a methane yield of 310 mL/g VS, representing 1.83- and 2.25-fold increases compared to the initial seed, respectively. The microbial community of E19 consisted of anaerobic fungi (uncultured Neocallimastigales, Anaeromyces sp., Orpinomyces sp., and Feramyces sp.) coexisting with anaerobic bacteria (streptomycin resistant Proteiniphilum acetatigenes), and methanogens. The E19 consortium was able to use various carbon sources (87.5%) and contained potential genes encoding enzymes involved in RS degradation. The microbial community of E19 was highly stable, making it a promising inoculum for biomass degradation, especially for anaerobic digestion to produce biogas.