Adaptive Responses to Oxidative Stress in the Filamentous Fungal Shiraia bambusicola.

Shiraia bambusicola can retain excellent physiological activity when challenged with maximal photo-activated hypocrellin, which causes cellular oxidative stress. The protective mechanism of this fungus against oxidative stress has not yet been reported. We evaluated the biomass and hypocrellin biosynthesis of Shiraia sp. SUPER-H168 when treated with high concentrations of H₂O₂. Hypocrellin production was improved by nearly 27% and 25% after 72 h incubation with 10 mM and 20 mM H₂O₂, respectively, while the inhibition ratios of exogenous 20 mM H₂O₂ on wild S. bambusicola and a hypocrellin-deficient strain were 20% and 33%, respectively. Under exogenous oxidative stress, the specific activities of catalase, glutathione reductase, and superoxide dismutase were significantly increased. These changes may allow Shiraia to maintain normal life activities under oxidative stress. Moreover, sufficient glutathione peroxidase was produced in the SUPER-H168 and hypocrellin-deficient strains, to further ensure that S. bambusicola has excellent protective abilities against oxidative stress. This study creates the possibility that the addition of high H₂O₂ concentrations can stimulate fungal secondary metabolism, and will lead to a comprehensive and coherent understanding of mechanisms against oxidative stresses from high hydrogen peroxide concentrations in the filamentous fungal Shiraia sp. SUPER-H168.