Fungal Isolates Enriched Under Anaerobic Conditions from Buffalo Rumen Fluid for Lignocellulosic Rice Straw Conversion and Biogas Production Potential

This study investigated fungal isolates enriched under strictly anaerobic conditions from buffalo (Bubalus bubalis) rumen fluid for their potential in lignocellulosic biomass conversion. Two isolates, B031 and E033, were obtained using serial dilution in Hungate tubes with cellobiose as a carbon source. Their characterization included morphological examination, ITS-5.8 S-LSU sequencing, substrate utilization profiling, and lignocellulosic degradation assays. Phylogenetic analysis indicated that B031 is related to uncultured Basidiomycota-affiliated fungi, while E033 is closely affiliated with the yeast-like fungus Trichosporon asahii. Although these taxa are not obligate anaerobic fungi, both isolates exhibited stable growth and sustained lignocellulosic degradation under oxygen-deprived conditions across successive anaerobic subcultures. Isolate B031 demonstrated greater versatility, achieving 60% microcrystalline cellulose (MCC), 66% lignin, and 58% rice straw degradation within 7 days, whereas E033 reached 55% MCC, 58% lignin, and 33% rice straw degradation. Given that rice straw is a major lignocellulosic residue in Thailand, these fungi have significant potential to enhance biogas conversion. Based on annual production of 23 million tons of rice straw, B031 could yield 3.93 billion Nm³ CH₄ (39.13 TWh primary energy; 13.70 TWh electricity), while E033 yielded 2.24 billion Nm³ CH₄ (22.26 TWh primary energy; 7.79 TWh electricity). These results highlight the importance of strain selection based on functional anaerobic degradation capacity rather than taxonomic affiliation alone and support the potential application of these isolates as bioaugmentation agents in anaerobic digestion systems. Further genomic and functional studies are recommended to refine their taxonomic classification and assess their practical application in sustainable biogas production.