Fungal Mn oxides supporting Mn(Ⅱ) oxidase activity as effective Mn(Ⅱ) sequestering materials

摘要

We examined the Mn(Ⅱ)-oxidizing ability of the biogenic Mn oxide (BMO) formed in cultures of a Mn(Ⅱ)-oxidizing fungus, Acremonium strictum strain KR21-2. The newly formed BMO effectively sequestered dissolved Mn(Ⅱ) mainly by oxidizing Mn(Ⅱ) to insoluble Mn under air-equilibrated conditions, and this ability lasted for at least 8 days. Deaerating the BMOs, poisoning them with NaN_3, or heating them all readily weakened their Mn(Ⅱ) oxidation ability, indicating the involvement of enzymatic Mn(Ⅱ) oxidation. There was no Mn(Ⅱ)-oxidizing ability observed for mycelia cultivated without Mn(Ⅱ) or for residual mycelia after the BMO phase was dissolved, suggesting the need for the oxide phase. A sodium dodecyl sulphate-polyacrylamide gel electrophoresis assay demonstrated that the oxide phase embeds the Mn(Ⅱ) oxidase and thereby maintains the enzymatic activity in BMOs. Freezing at -80℃ preserved the Mn(Ⅱ)-oxidizing ability in BMOs for at least 4 weeks, while lyophilization caused a complete loss of this ability. Based on these results, we propose that fungal Mn oxides supporting Mn(Ⅱ) oxidase activity are an effective Mn(Ⅱ)-sequestering material capable of oxidizing Mn(Ⅱ) continuously from solutions containing no additional nutrients to maintain biological activity.