Nickel sulfide, iron-nickel sulfide and iron sulfide precipitation by a newly isolated Desulfotomaculum species and its relation to nickel resistance
A Desulfotomaculum sp. (DF-1) isolated from a sulfate reduction bioremediation pilot plant in Chengdu (P.R.C.) was resistant to 360 (6.1 mM), 450 (7.7 mM), and 550 ppm (9.4 mM) Ni(II) in the presence of 0, 100 (1.8 mM), and 200 ppm (3.6 mM) Fe(II), respectively. When cultured in the presence of Ni (II) with or without Fe, DF-1 produced a dark-brown, soluble product. Only small amounts of Ni and or Fe were precipitated at the cell surface when cells were subjected to 100 ppm concentrations of the metals. However, in the presence of Fe(II) only, large amounts of FeS (70% of the Fe) were precipitated at the bacterial cell surface and extracellularly. The increase of Ni in the growth medium was inversely related to the concentration of Fe precipitated as a sulfide. This coincided with the formation of dark-brown, soluble Ni-proteins, consisting of a range of polypeptides from approx. 70–120 kDa, which inhibited NiS formation and promoted Fe-complexation. These autolysis-inducible proteins and cell wall autolysis by-products bound Ni, and are thought to confer Ni-resistance in DF-1. Harsh treatments, such as acidification of culture supernatants from Ni-grown DF-1, destabilized the Ni-organic complexes, and resulted in the precipitation of an amorphous Ni-rich material.