Aerobic H(2) 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 (H(2)) functions as a signaling molecule for physiological processes such as stress responses. Here, it is demonstrated that white-rot fungi produce H(2) during wood decay. The white-rot fungus Trametes versicolor produces H(2) from wood under aerobic conditions, and H(2) production is completely suppressed under hypoxic conditions. Additionally, oxalate and formate supplementation of the wood culture increased the level of H(2) 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 H(2) 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 H(2) production by this fungus. It is expected that this novel finding of aerobic H(2) production from wood biomass by a white-rot fungus will open new fields in biohydrogen research.