Effect of oxygen concentrations and branched-chain amino acids on the growth and development of sub-seafloor fungus, Schizophyllum commune 20R-7-F01.

Fungi have been reported to be the dominant eukaryotic group in anoxic sub-seafloor sediments, but how fungi subsist in the anoxic sub-marine sedimental environment is rarely understood. Our previous study demonstrated that the fungus, Schizophyllum commune 20R-7-F01 isolated from a ~2 km sediment below the seafloor, can grow and produce primordia in the complete absence of oxygen with enhanced production of branched-chain amino acids (BCAAs), but the primordia cannot be developed into fruit bodies without oxygen. Here, we present the individual and synergistic effects of oxygen and BCAAs on the fruit-body development of this strain. It was found that the fungus required a minimum oxygen concentration of 0.5% pO2 to generate primordia and 1% pO2 to convert primordia into mature fruit body. However, if BCAAs (20 mM) were added to the medium, the primordium could be developed into fruit body at a lower oxygen concentration up to 0.5% pO2 where genes fst4 and c2h2 playing an important role in compensating oxygen deficiency. Moreover, under hypoxic conditions, the fungus showed an increase in mitochondrial number and initiation of auto-phagocytosis. These findings suggest that the fruit-body formation of S. commune may have multiple mechanisms, including energy and amino acid metabolism in response to oxygen concentrations.