While we all know mercury is poisonous it is methylmercury, the organic form, that bioaccumulates in food webs and is highly toxic. It's been acknowledged for years that methylmercury is produced by microorganisms far down the food chain, but what has not been known is how they do it. US-based researchers at Oak Ridge National Laboratory in Tennessee have now identified the genes, and hence the proteins, involved in mercury methylation and suggest that the pathway is common for all mercury methylating microorganisms.
Using gene deletion, Jerry Parks' team showed that two genes are key components of bacterial mercury methylation, relating to a corrinoid protein that acts as a methyl carrier and a ferredoxin protein that reduces the corrinoid protein's cofactor. What is still not apparent, however, is why these bacteria have evolved to methylate mercury at all.