Aerobic H₂ production related to formate metabolism in white-rot fungi

Biohydrogen is mainly produced by anaerobic bacteria, anaerobic fungi, and algae under anaerobic conditions. In higher eukaryotes, it is thought that molecular hydrogen (H₂) functions as a signaling molecule for physiological processes such as stress responses. Here, it is demonstrated that white-rot fungi produce H₂ during wood decay. The white-rot fungus Trametes versicolor produces H₂ from wood under aerobic conditions, and H₂ production is completely suppressed under hypoxic conditions. Additionally, oxalate and formate supplementation of the wood culture increased the level of H₂ evolution. RNA-seq analyses revealed that T. versicolor oxalate production from the TCA/glyoxylate cycle was down-regulated, and conversely, genes encoding oxalate and formate metabolism enzymes were up-regulated. Although the involvement in H₂ production of a gene annotated as an iron hydrogenase was uncertain, the results of organic acid supplementation, gene expression, and self-recombination experiments strongly suggest that formate metabolism plays a role in the mechanism of H₂ production by this fungus. It is expected that this novel finding of aerobic H₂ production from wood biomass by a white-rot fungus will open new fields in biohydrogen research.