The present invention relates to a mutant CC3625 cysteine synthase. Bacteria containing such mutant cysteine synthase can be used for the precipitation of soluble lead.

Cysteine synthase or O-Acetyl-L-Serine Sulfhydrylase enzymes, such as those derived from the Aeropyrum pernix bacterium, may be used in additive compositions, fluid compositions, and methods for decreasing or removing hydrogen sulfide from recovered downhole fluids and/or the subterranean reservoir wellbore from which the downhole fluid was recovered. The fluid composition may include at least one cysteine synthase enzyme and a base fluid, such as a drilling fluid, a servicing fluid, a production fluid, a completion fluid, an injection fluid, a refinery fluids, and combinations thereof.

The purpose of the present invention is to provide a method for producing selenoneine that allows production of selenoneine at higher yields, even if an inorganic selenium compound is used as a selenium compound. This purpose can be achieved by a method for producing selenoneine, comprising the step of applying histidine and a selenium compound to a transformant to obtain selenoneine, wherein the transformant has at least one gene selected from the group consisting of a SatA gene, a CysB gene and a MetR gene, and an EgtA gene inserted therein and can overexpress the inserted genes.