The paper for today is:
Parks, J.M. et al. (2013). The Genetic Basis for Bacterial Mercury Methylation. Science, 339(6125), pp. 1332-1335. doi:10.1126/science.1230667.

(There is a tiny dog in this room and its constant yelpings and mewlings are making it quite hard to absorb this material.)

This is a quick little report about the genes used by mercury-methylating microbes to do their mercury-methylating work. The authors already knew about the corrinoid iron-sulfur protein (CFeSP) used to methylate metallic clusters on acetyl-CoA synthases, so they began to look for something similar in the genomes of mercury-methylating bacteria. They did find one within a Desulfovibrio desulfuricans genome along with a gene for a putatively associated ferredoxin. It's not just D. desulfuricans, either: the same pair of genes appears to be present in 51 other genome sequences, at least a few of which are known to be mercury-methylators. Beyond the bioinformatics, D. desulfuricans deletion mutants without these two genes appeared to grow normally yet had almost none of their usual Hg-methylating ability.

It is entirely possible that the two target genes in this study - referred to the authors as hgcA and hgcB - have some other functions. The genomes of some distantly related species do appear to contain hgcAB orthologs, including a set in the recently isolated Methanomassiliicoccus luminyensis, a commensal human gut-dwelling archaeon. It isn't clear why many of these species code for these enzymes or need anything like them at all. Studies of microbial metal metabolism look like another job for the "sequence everything that moves" approach.