Bacteria arsenite compounds

Several inorganic arsenic compounds are weak inducers of chromosomal aberrations, sister chromatid exchange, and in vitro transformation of mammalian and piscine cells. However, there is no conclusive evidence that arsenic causes point mutations in any cellular system (Pershagen and Valuer 1979 Belton et al. 1985 Lee et al. 1985 Deknudt et al. 1986 Manna and Mukheijee 1989). Studies with bacteria suggest that arsenite is a comutagen, or may inhibit DNA repair (Belton et al. 1985). 

Thermodynamic considerations suggest that in oxygenated seawater, arsenic should exist almost entirely as arsenate (71). It was apparent from the early work on arsenic in seawater, however, that arsenite was also present in significant concentrations and could at times predominate over arsenate (7,8, 72, 73). Marine bacteria (74) and marine phytoplankton (75) were shown to reduce arsenate to arsenite, thereby providing an explanation for the observed As(III)/As(V) ratio in seawater. The compounds MMA and DMA also occur in seawater, generally as minor constituents (9, 34, 71, 76). The concentrations of As(III), MMA, and DMA are positively correlated with primary productivity,... 

Methylation of arsenic is an important pollution problem because of the widespread use of arsenic compounds in insecticides and because of the presence of arsenate in the phosphate used in household detergents.421 422 After reduction to arsenite, methylation occurs in two steps (Eq. 16-45). Additional reduction steps result in the formation of dimethylarsine, one of the principal products of action of methanogenic bacteria on arsenate. The methyl transfer is shown as occurring through CH3+, with an accompanying loss of a proton from the substrate. However, a CH3 radical may be transferred with formation of a cobalt(II) corrinoid.423... 

The marine facultative anaerobe bacterium Serratia marinoruhm and the yeast Rhodotoruhi rubra both methylate arsenate ion to methylarsonate, but only the latter produces cacodylic acid (258). Human volunteers who ingested 500 fig doses of As as sodium arsenite, sodium methylarsonate, and sodium cacodylate excreted these compounds in their urine (259). Of these three, approximately 75% of the sodium arsenite is methylated, while 13% of methylarsonate is methylated. Rat liver subcellular fractions methylated sodium arsenate in vitro, providing the first direct evidence for possible mammalian methylation independent of symbiotic bacteria (260). Shariatpanahi el al. have reported kinetics studies on arsenic biotransformation by five species of bacteria (261). They found that the As(V)-As(IIl) reduction followed a pattern of two parallel first-order reactions, while the methylation reactions all followed first-order kinetics. Of the five species tested, only the Pseudomonas produced all four metabolites (arsenite, methylarsonate, cacodylate, trimethylarsine) (261). 

Chen et al. [77] studied metabolites of dimethylar-sinic acid in the urine of rats exposed to DMA in drinking water. Anion-exchange chromatography was used to monitor the increased concentrations of arsenite, DMA, trimethylarsine oxide and an unidentified compound in the urine. Results showed that DMA was demethylated to inorganic As which is achieved by the action of intestinal bacteria. 

Redox reactions in soils are affected by a number of parameters, including temperature, pH (see Chapter 7), and microbes. Microbes catalyze many redox reactions in soils and use a variety of compounds as electron acceptors or electron donors. For example, aerobic heterotrophic soil bacteria may metabolize readily available organic carbon using NO3, NOj, N20, Mn-oxides, Fe-oxides and compounds such as arsenate (As04 ) and selenate (Se04 ) as electron acceptors. Similarly, microbes may use reduced compounds or ions as electron donors, for example, NH4, Mn2+, Fe2+, arsenite (AsCXj), and selenite (SeO ). 

The arsenic cycle in ocean waters and sediments also has important biological steps (Andreae, 1979). Arsenate, As(V), can be biologically converted into arsenite, As(III), and at least eight different organo-arsenic compounds, all presumably representing detoxification processes mediated by bacteria in... 

Methylation of Inorganic oxyarsenic anions occurs in organisms ranging from microbial to mammalian methylated and products include arsenocholine, arsenobetaine, dimethylarsinic acid, and methylarsonic acid arsenite methyltransferase and monomethylarsonic acid methyltransferase use S-adenosylmethionine for the methyl donor Boron biochemistry essentially that of boric acid, which forms ester complexes with hydroxyl groups, preferably those adjacent and cis, in organic compounds. Five naturally occurring boron esters (all antibiotics) synthesized by various bacteria have been characterized Exists as Br Ion in vivo, binds to proteins and amino acids... 

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