biogenic mn oxides (bmos) are naturally occurring mn oxides that have the ability to oxidize various redox-sensitive elements. "a. strictum" is a mn(ii)-oxidizing fungus that forms bmos through the action of mn(ii) oxidase. in the presence of bmos in buffer solutions with no additional nutrients, "a. strictum" is capable of sequestering high mn(ii) concentrations for at least 8 days, in which the amount of dissolved mn(ii) decreases rapidly in several hours and is converted to oxidized mn(ii). deaeration of the buffer solution with n gas purging suppressed mn(ii) conversion, but this suppression is easily rescued by aeration, implying that dissolved oxygen is required for the mn(ii) sequestration and oxidation process. adding nan, a toxic substance, also significantly reduces the sequestration rates of the fungal bmos. heat treatments revealed that temperatures below 85 °c do not alter the conformation of the mn(ii) oxidase in the bmos. freezing the fungal bmos at -80 °c for 4 weeks did not affect the mn(ii) ability, and the reducible mn was still dominated in solution. this makes fungal bmos an effective mn(ii) sequestering material if needed. for example, it can be used for the continuous removal of mn(ii) from mn(ii) contaminated water without the need for any additives other than dissolved oxygen. the product is an oxide phase mn(ii) that would provide additional affinity for other toxic elements and thus prove as an effective method of water cleansing. enzymatically active fungal bmos can be harvested under specific cultivation conditions and remain active even under circumstances that would be unfavourable for fungal growth.