Anaerobic reduction

A few details have been reported on the slow reductions of 8303 by As(ni) and T1(I) . In the anaerobic reductions by As(III) the reaction is first-order in 820 and although As(III) certainly catalyses decomposition, the dependence of the rate on [As(III)] is small. Aeration leaves the rate of spontaneous decomposition of 820g unaffected, but the As(III)-catalysed route is accelerated by a factor of ten, the kinetic law remaining unchanged. The oxygen effect is interpreted in terms of the chain reaction... 

Myers CR, KH Nealson (1990) Respiration-linked proton translocation coupled to anaerobic reduction of manganese(IV) and iron (III) in Shewanella putrefaciens. J Bacteriol 172 6232-6238. 

Ran J, H-J Knackmuss, A Stolz (2002) Effects of different quinoid redox mediators on the anaerobic reduction of azo dyes by bacteria. Environ Sci Technol 36 1497-1504. 

Determinations of 8 " S have been extensively used in studies on the sulfur cycle, including reactions involving microbial anaerobic reduction of sulfate and thiosulfate (Smock et al. 

Kudlich M, Keck A, Klein J, Stolz A (1997) Localization of the enzyme system involved in anaerobic reduction of azo dyes by Sphingomonas sp. strain BN6 and effect of artificial redox mediators on the rate of azo dye reduction. Appl Env Microbiol 63 3691-3694... 

Kudlich M, Hetheridge MJ, Knackmuss HJ, Stolz A (1999) Autoxidation reactions of different aromatic o-aminohydroxynaphthalenes that are formed during the anaerobic reduction of sulfonated azo dyes. Env Sci Technol 33 869-901... 

Guo JB, Zhou JT, Wang D et al (2007) Biocatalyst effects of immobilized anthraquinone on the anaerobic reduction of azo dyes by the salt-tolerant bacteria. Wat Res 41 426-432... 

Reduced flavins (FADH2, FMNH2, and riboflavin) generated by flavin-dependent reductases have been hypothesized to reduce azo dyes in a nonspecific chemical reaction, and flavin reductases have been revealed to be indeed anaerobic azoreductases. Other reduced enzyme cofactors, for example, NADH, NADH, NADPH, and an NADPH-generating system, have also been reported to reduce azo dyes. Except for enzyme cofactors, different artificial redox mediating compounds, especially such as quinines, are important redox mediators of azo dye anaerobic reduction (Table 1). 

Diniz PE, Lopes AT, Lino AR (2002) Anaerobic reduction of a sulfonated azo dye Congo Red by sulphate reducing bacteria. Appl Biochem Biotechnol 97 147-163... 

Azo dye molecules have color due to their azo bond, auxochromes, and system of conjugated double bonds. The azo bond, while resistant to aerobic degradation, can be cleaved under anaerobic or anoxic condition, resulting in decolorization and the production of aromatic amines. Anaerobic reduction of the azo dyes is relatively easy to achieve, but the products have been found to be biorecalcitrant... 

To reach the reductive step of the azo bond cleavage, due to the reaction between reduced electron carriers (flavins or hydroquinones) and azo dyes, either the reduced electron carrier or the azo compound should pass the cell plasma membrane barrier. Highly polar azo dyes, such as sulfonated compounds, cannot pass the plasma membrane barrier, as sulfonic acid substitution of the azo dye structure apparently blocks effective dye permeation [28], The removal of the block to the dye permeation by treatment with toluene of Bacillus cereus cells induced a significant increase of the uptake of sulfonated azo dyes and of their reduction rate [29]. Moreover, cell extracts usually show to be more active in anaerobic reduction of azo dyes than whole cells. Therefore, intracellular reductases activities are not the best way to reach sulfonated azo dyes reduction the biological systems in which the transport of redox mediators or of azo dye through the plasma membrane is not required are preferable to achieve their degradation [13]. 

Certainly, considerable flexibility and adaptability of electron flow is expected in bacteria, and many new strains are expected to be found that obtain energy from these chemical reductions. The natural gene flow over the years in the anaerobic ecosystems has produced microorganisms of considerable physiologic diversity. These anaerobic organisms continue to provide numerous biochemical challenges in the areas of anaerobic reduction of metals, metalloids, and nonessential elements by microorganisms. 

The anaerobic reduction of metal ions, including ferric iron (Fe(III)) to ferrous iron (Fe(II)) by microorganisms, has been observed for >80 years (Harders 1919) and was reviewed several times from various viewpoints (Jones 1986 Lovley 1991, 1995 Nealson and Saffarini 1995). In general terms the process can be described by ... 

Balashova VV, Zavarzin GA. 1980. Anaerobic reduction of ferric iron by hydrogen bacteria. Microbiology 48 635-9. 

Aromatic amines can be introduced into the environment from different anthropogenic activities. They are often present in untreated wastewaters from dye industries [45-48] in particular, sul-fonated amines have been found in municipal biological treatment plants and sediments of rivers, formed likely through the cleavage of the azo bonds, induced by anaerobic reduction [49],... 

Laccase, 36 318, 329, 40 122 see also Blue copper oxidases amino-acid sequences, 40 141 anaerobic reduction, 40 158-160 biological function, 40 124 electrochemistry, 36 360 fungal, 40 145-152 evolution, 40 153-154 inhibition, 40 162 kinetic properties, 40 157-162 molecular and spectroscopic properties, 40 125-126... 

---