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Microbial methylation and volatilization of arsenic Lehr, Corinne Rita


The basis of the "Toxic Gas Hypothesis" of Sudden Infant Death Syndrome (SIDS) is that the microorganisms present on infants bedding materials volatilize sufficient arsenic, antimony or phosphorus from these materials to be acutely toxic to an infant. The volatilization of arsenic by aerobic microorganisms isolated from new sheepskin bedding materials, as well as from materials used by a healthy infant and by an infant who perished of SIDS was examined. Three arsenic-methylating fungi were isolated from a piece of sheepskin bedding material on which an infant perished of SIDS. These fungi form trimethylarsenic(V) species, precursors to volatile trimethylarsine. Their ribosomal RNA PCR products were used to identify the fungi as Scopulariopsis koningii, Fomitopsis pinicola and Penicillium gladioli. S. koningii, as well as two other sheepskin isolates, Mycobacterium neoaurum and Acinetobacter junii are human pathogens which should also be of concern in connection with SIDS. Few microogransism have been shown to methylate antimony. S. koningii methylated the antimony(III) compounds, potassium antimonyl tartrate and antimony trioxide yielding trimethylantimony. P. gladioli and S. koningii volatilized arsenic as trimethylarsine, but only under conditions such that the production of sufficient trimethylarsine to be acutely toxic to an infant is urilikely. These fungi did not volatilize antimony. Very little is known about the demethylation of methylarsenicals. One of the sheepskin isolates, Mycobacterium neoaurum, demethylated methylarsenic compounds to mixtures of As(III) and As(V). There was some evidence that MMA(V) is reductively demethylated to As(III) which is then oxidized to As(V). Iodide decreased the demethylation of MMA(V) by M. neoaurum and increased the methylation of MMA(V) by both P. gladioli and S. koningii. The techniques developed for studying the volatilization of arsenic by the microorganisms on sheepskin bedding materials were applied to two other environments - garden waste compost and Meager creek hot springs. Composting of garden waste yielded iodomethane. Aerobic incubation of microbial mats and sediment from Meager creek hot springs yielded trimethylarsine and trimethylstibine.

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