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.