Abstract
In this study the bioconversion of bismuth to volatile derivatives was investigated in cultures of the common sewage sludge methanogen Methanobacterium formicicum. The production of volatile bismuth compounds was analysed during growth of M. formicicum with respect to the concentration and chemical formulation of the applied bismuth. The main volatile bismuth compound detected in the culture headspace was trimethylbismuth (TMBi), with a maximum conversion rate of up to 2.6 ± 1.8% from spiked 1 µM bismuth nitrate [Bi(NO~3~)~3~] in the culture media. This main compound proved to be stable under the incubation conditions in a CO~2~–H~2~ atmosphere. Bismuthine and the partially methylated bismuthines monomethylbismuth hydride and dimethylbismuth hydride were additionally detected in the late exponential growth phase, but only in the presence of low concentrations of spiked Bi(NO~3~)~3~ (10 nM, 100 nM). The conversion of bismuth to TMBi from the bismuth‐containing pharmaceuticals Bismofalk® [containing bismuth subgallate and Bi(NO~3~)~3~] and Noemin® (containing bismuth aluminate) could also be observed, however, with a lower rate than found for Bi(NO~3~)~3~. In vitro experiments with crude extracts of M. formicicum suggest that the methylation of bismuth is mainly catalysed by enzyme‐catalysed reactions with methylcobalamin as methyl donor. Copyright © 2002 John Wiley & Sons, Ltd.