Reduction with microorganisms

Anaerobic reduction of Se04 and SeO to Se° and methylated selenides Selenate and selenite reduction by microorganisms has been noted for some time. Organisms with this capacity include bacteria and fungi (Trudinger et al., 1979 Stolz Oremland, 1999). In bacteria the reductions are mostly a form of anaerobic respiration and result in selenium immobilization with the formation of water-insoluble Se°. In fungi the reductions involve the formation of methylated selenium,... 

The widely occurring reduced carvones are formed (in 100% optical purity) by reduction with various microorganisms. A most interesting point is that each stage in the reduction is accompanied by a fall in the toxicity. For example, (— )-carvone (281) was reduced by Tetrahymena pyriformis successively to (+)-... 

Most studies in the microbial metabolism of nitroaromatic compounds used aerobic microorganisms. In most cases no mineralization of nitroaromatics occurs, and only superficial modifications of the structures are reported. However, under anaerobic sulfate-reducing conditions, the nitroaromatic compounds reportedly undergo a series of reductions with the formation of amino compounds. For example, trinitrotoluene under sulfate-reducing conditions is reduced to triaminotoluene by the enzyme nitrite reductase, which is commonly found in many Desulfovibrio spp. The removal of ammonia from triaminotoluene is achieved by reductive deamination catalyzed by the enzyme reductive deaminase, with the production of ammonia and toluene. Some sulfate reducers can metabolize toluene to (X) sub 2. Similar metabolic processes could be applied to other nitroaromatic compounds like nitrobenzene, nitrobenzoic acids, nitrophenols, and aniline. Many methanogenic bacteria can reduce nitroaromatic compounds to amino compounds. 

The use of microorganisms other than baker s yeast can be advantageous. While baker s yeast reduction of 2,3-octanedione leads to a mixture of (S)-2-hydroxy-3-octanonc, the isomeric ketol, (3S)-3-hydr0xy-2-octanone and the (25,3/ )-2,3-octanediol, reduction with the fungus Beauveria sulfurescens gives only (25,3S)-2,3-octanediol in enantiomerically pure form222. 

In addition to baker s yeast, many other microorganisms have been used for the reduction of cyclic ketones. In contrast to the yeast transformation of 6-oxobicyclo[3.2.0]hept-2-ene to the isomeric alcohols (vide supra), the reduction with Mortierella ramaniana proceeds selectively to yield only the (6S)-eHcfe>-alcohol and unreacted optically active ketone274. If the same fungus is used for the reduction of 7.7-dimethyl-6-oxobicyclo[3.2.0]hept-2-ene a mixture of endo- and e.w-alcohols is formed275. 

Beyond the biological process of sullate reduction with subsequent metal precipitation as sulfides, other mechanisms of metal removal can be present during the runs, particularly in the inoculated column (A) precipitation as metals carbonates using the bicarbonate and/or carbonates formed during the reduction of sulfate by the SRB cells or by fermentation from other microorganisms, precipitation as metal hydroxides, complexing with substances excreted by the cells, and accumulation on the surface of cells, through reactions between metal ions and cell wall components [10]. 

DDD is the major product when DDT is incubated anaerobically with microorganisms. This reductive dechlorination has occurred in many but not all of the aerobic studies. Aerobacter aerogenes has been studied aerobically and anaerobically in parallel experiments. In some cases the reaction was similar under both conditions (16 17), but it was suggested that anaerobic conditions increased the yield of DDD (18), In contrast... 

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