Bacteria, manganese-oxidizing species

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

Disproportionation reactions do not cause a net oxidation of the sulfur species, yet they have a key function in sulfide oxidation. Disproportionation provides a shunt in the sulfur cycle whereby the H S formed by this reaction may be oxidized again to the same sulfur intermediate by metal oxides. Manganese oxide, for example, rapidly oxidizes H S to S without participation of bacteria, but does not oxidize the S further to sulfate (Burdige 1993). The elemental sulfur may, however, be disproportionated (Eq. 8.19) whereby a fourth of it is oxidized completely to sulfate while the remaining three fourths return to the sulfide pool. Through repeated partial oxidation of sulfide to elemental sulfur with manganese oxide and subsequent disproportionation of the elemental sulfur to sulfate and sulfide a complete oxidation of sulfide to sulfate by manganese oxide may be achieved (Fig. 8.16 Thamdrup et al. 1993 Bdttcher and Thamdmp 2001) ... 

Influence of Some Microbiological Species on Corrosion.64 Some bacteria are involved directly in the oxidation or reduction of metal ions, particularly iron and manganese. 

Bryant MP, Wolin EA, Wolin MJ, Wolfe RS (1967) Methanobacillus omelianskii, a symbiotic association of two species of bacteria. Arch Microbiol 59 20-31 Cammack R, Chapman A, Lu W-P, Kargouni A, Kelly DP (1989) Evidence that protein B of the thiosulfate-oxidizing system of Thiobacillus versutus contains a binuclear manganese cluster. FEBS Lett 253 239-243... 

Mariganese-containing catalases have been isolated from three species of bacteria Lactobacillus plantarum [27], Thermus ihemtophUus [28], and Thermoleophilum album [18]. X-ray crystallographic structure analysis [29] has shown that these catalases contain a dinudear manganese core. During catalysis, the dinudear manganese active site cydes between the Mn"- and Mn2"oxidation states [30]. 

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