Cysteine synthase enzymes (e.g. O-Acetyl-L-Serine Sulfhydrylase enzymes) may be used in combination with sulfide quinone reductase enzymes 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 with at least one sulfide quinone reductase, and a base fluid, such as a water-based fluid, an organic-based fluid, and combinations thereof.