Bacteria arsenic volatilization

The methylation of arsenic is entirely or almost entirely biotic (Frankenberger and Arshad, 2002), 367. Specifically, certain fungi (including yeasts) and bacteria are capable of methylating arsenic ((Bentley and Chasteen, 2002), 257-260 (Cullen and Reimer, 1989), 717-724 Chapter 4). Only limited evidence exists for the chemical (abiotic) methylation of arsenic. As mentioned earlier, some volatile arsines have been produced in the laboratory from photochemical reactions involving As(III), carboxylic acids, and ultraviolet radiation (Guo et al., 2005 McSheehy et al., 2005). 

Methane bacteria have been shown to catalyze reactions in which the active methyl group is transferred to acceptors such as arsenate or mercury. When extracts are incubated in a hydrogen atmosphere with methylcobalamin, arsenate, and ATP, a volatile arsine derivative is formed (20). Arsines are difficult and dangerous to work with they are extremely poisonous and are oxidized rapidly in air. Fortunately they have an intense garhc odor so the investigator is warned of their presence. 

The stability of a reference material is of great importance since the same material may be used over a period of many years. At issue is not only the question of whether it continues to be pleasant to handle (biological materials can of course be attacked by bacteria, fungi, insects and other pests), but also that, due to evaporation or chemical reactions, the concentrations and chemical binding of some of the elements of interest may change. This is obviously of greatest concern for elements that can exist in a volatile form such as mercury and arsenic, which could thereby be lost. 

Chiu et al. (53) reported that lowering of soil redox potential increased the ratio of As(III) and promoted arsenic methylation. Methylation of arsenic compounds by yeast and bacteria under oxic conditions plays a significant role, whereas methanogenic bacteria are important under anoxic conditions in releasing volatile arsenic from the soil to the atmosphere (39,41). Woolson and Kearney... 

For example, bacteria living in landfill sites can metabolize the arsenic present in such sites to volatile arsines. For the determination of these highly toxic ultratrace compounds by GC it is necessary to have a series of cleanup steps if GC is coupled to electron impact mass spectrometry (GC-MS) or ICP-MS, since the samples contain dozens of different organic... 

Bacteria, anaerobic and aerobic, have the same ability to methylate arsenic. The volatile products can be fully methylated, Me3As, but they can also be arsines with As-H bonds, e.g. MeAsH2- For example, starting with As(V), Pseudomonas sp affords As(III), CH3ASH2, (CH3)2AsH, and (CH3)3As and Flavobacterium sp affords As(III) and (CH3)2AsH(11). 

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