title: Response to mercury (II) ions in Methylococcus capsulatus (Bath).
abstract: The mercury (II) ion is toxic and is usually detoxified in Bacteria by reduction to elemental mercury, which is less toxic. This is catalysed by an NAD(P)H-dependent mercuric reductase (EC 1.16.1.1). Here, we present strong evidence that Methylococcus capsulatus (Bath) - a methanotrophic member of the Gammaproteobacteria - uses this enzyme to detoxify mercury. In radiorespirometry studies, it was found that cells exposed to mercury dissimilated 100% of [(14) C]-methane provided to generate reducing equivalents to fuel mercury (II) reduction, rather than the mix of assimilation and dissimilation found in control incubations. The detoxification system is constitutively expressed with a specific activity of 352 (±18) nmol NADH oxidized min(-1)  (mg protein)(-1) . Putative mercuric reductase genes were predicted in the M. capsulatus (Bath) genome and found in mRNA microarray studies. The MerA-derived polypeptide showed high identity (> 80%) with MerA sequences from the Betaproteobacteria.
authors.affiliation: School of Life Sciences, University of Warwick, Coventry, UK. rich.boden@warwick.ac.uk
authors.forename: Rich
authors.initials: R
authors.lastname: Boden
authors.forename: J Colin
authors.initials: JC
authors.lastname: Murrell
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D008628:Mercury / Q000378:metabolism*; D020619:Methylococcus capsulatus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D009243:NAD; D009249:NADP; D010088:Oxidoreductases; C021551:mercuric reductase; D008628:Mercury