Microorganisms manganese oxidation

Soil pH affects the transformation of Cr between Cr(III) and Cr(VI) in soils. Since Cr(VI) has greater bioavailability and mobility in soils than Cr(III), which is strongly bound by soil solid matrix (Han and Banin, 1997). Cr(III) can be oxidized by soil manganese oxides into Cr(VI), while Cr(VI) can be reduced by organic matter, Fe(II) and microorganisms in soils. Reduction of Cr(VI) has been found to occur much slower in alkaline soils compared to acid soils (Cary et al., 1997). 

Iron and manganese oxides are the most abundant components of Earth s surface that can serve as anaerobic terminal electron acceptors in microbial metabolism, yet it was recognized only recently that microorganisms play a key role their cycling. Despite early reports that suggested biological Fe(III) reduction was important in wet... 

Manganese-oxidizing and -reducing microorganisms may be isolated from the same site within particular ecosystems (Ehrlich et al., 1972), but conditions necessary for oxidation and reduction are different and these processes are unlikely to occur simultaneously. Specific situations where microorganisms are significant in manganese transformations will be considered later. 

Krumbein, W.E. and Altmann, H.J., 1973. A new method for the detection and enumeration of manganese oxidizing and reducing microorganisms. Helgol. Wiss. Meeresunters., 25 347—356. 

Ten Khak-Mun., 1967. Iron- and manganese-oxidizing microorganisms in soils of South Sakhalin. Microbiology, 36 276—281. 

Ten Khak-Mun., 1969. A new soil microorganism which oxidizes manganese. Dokl. Akad. Nauk USSR, 188 697-699 (in Russian). 

Manganese is cycled by microorganisms in similar ways to iron. Mineralization of manganese oxides (e.g., bimessite) is often attributed to a variety of bacteria, including Gallionella, Leptothrix, Sphaerotilus, Pseudomonas, and Pedomicrobium spp. Enzymes involved in Mn oxidation have been studied in some detail (e.g., Brouwers et al. 2000). 

Photolysis in surface waters may transform a part of this recalcitrant DOM into low molecular weight compounds that are available for microbial uptake (Mopper et al. 1991 Hedges 1992). Manganese oxides have also been reported to oxidize humic substances spontaneously, forming some simple compounds such as acetaldehyde and pyruvate, which are readily assimilable by microorganisms (Sunda Kieber 1994). 

In natural systems microbiological oxidation may offer a faster pathway, particularly at pH < 8 and low concentrations (<5 jlM) of particulate oxides. Hastings and Emerson (17) showed that sporulated cultures of marine bacillus SG-1 at pH 7.5 accelerated the oxidation of Mn(II) by a factor of 104 with respect to the abiotic catalysis on a colloidal MnOz surface. A radiotracer study of microbial Mn oxidation in a marine fjord revealed half-lives as short as 2 days (18). Perhaps microorganisms can use the entire redox cycle of manganese. A study indicates that the vegetative cells of spores that mediate Mn(II) oxidation also reduce manganese oxides (19). 

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