Abstract:

Manganese oxide minerals in soils are the products of the weathering of primary mineral and the process of soil formationAs one family of most active minerals in reactions, they play a crucial role in the biological geochemical cycling of many elements through impacting these elements speciation, transport and conversion in natural environmentsConsequently, the formation mechanism and environmental behaviors of manganese oxide minerals are one of the hot topics in the fields of soil science, sedimentology, oceanography and material scienceIt has been indicated in literatures that the genesis of manganese oxide in the environment is closely related to the microbiological process, and microbial mediated oxidation of aqueous Mn(II) can greatly accelerate the rate of oxidation up to five orders of magnitude faster than surfacecatalyzed reactionsMicroorganisms, including bacteria and fungi, that participate in oxidation of Mn(II) are widespread in natureAll of the known typical Mn(II) oxidizing bacteria belong to the Firmicutes, Actinobacteria and Proteobacteria branches of the Domain BacteriaThey enzymatically catalyze the oxidation of Mn(II) by a kind of putative multicopper oxidase in extracellular polymeric substances The bacterial oxidation of Mn(II) to Mn(IV) proceeds as  two sequential quick oneelectron transfer processes with the occurrence of an intermediate of  soluble transient Mn(III)The initial biogenic manganese oxide is a kind of phyllomanganate mineral, similar to δMnO2 or acid birnessite, with low degree of crystallanity, small particle size, high oxidation state of Mn and high proportion of octahedral vacancy sitesTherefore, it exhibits a more active surface reactivity such as adsorption and redox reactionsThe relationship of  microbially mediated oxidation of Mn(II) and  the formed Mn(III) intermediates to the global geochemical cycling of liferelated elements such as C, N and S is needed of us to pay attention to in the future.

Key words:

manganese oxide mineral; microbial Mn(II) oxidation; Mn bacteria; biological genesis; multicopper oxidase; environmental behavior; surface chemical properties; adsorption; redox