Anaerobic production and biosynthesis mechanism of exopolysaccharides in Schizophyllum commune 20R-7-F01

Exopolysaccharides (EPS) produced by microorganisms play a vital role in physiological and ecological processes. However, the mechanisms of EPS synthesis and release in anaerobic environments remain poorly understood. Here, we provide the first evidence of anaerobic EPS synthesis by the fungus Schizophyllum commune 20R-7-F01, isolated from coal-bearing sediments ~2.0 km below the seafloor. Under anaerobic conditions, the fungus exhibited significantly higher specific EPS production (1.57 times) than under aerobic conditions. Transcriptomic analysis revealed 2057 differentially expressed genes (DEGs) in the strain cultured anaerobically for 7 days compared to aerobically. Among these genes, 642 were significantly upregulated, while 1415 were significantly downregulated, mainly associated with carbon metabolism pathways. Genes involved in glycolysis and EPS synthesis, including hexokinase (HK), phosphoglucomutase (PGM), and (1 → 3)-β-glucan synthase (GLS), were significantly upregulated, while those related to the TCA cycle, respiratory chain, and pentose phosphate pathway were downregulated under anaerobic conditions. These findings highlight the oxygen-dependent regulation of EPS synthesis and suggest that EPS may serve as a key mechanism for fungal adaptation to anaerobic environments.