Sulfate requirement for heterotrophic growth of "ferroplasma acidarmanus" strain fer1

Growth of the acidophilic archaeon, "Ferroplasma acidarmanus" strain fer1, in a laboratory medium (primary constituents, FeSO₄ 72 mM and 0.02% yeast extract) is minimal. A survey of the annotated genome revealed metabolic transporters for Ni²⁺, sugars, and amino acids. Accordingly, the concentration of yeast extract was increased to 0.1% and the addition of 2 mM Ni(NH₄)₂(SO₄)₂ significantly enhanced the cultivation of strain fer1. The maximum optical density in the modified fer1 medium (mfer) was OD492=0.27 with 10¹⁰ viable cells / ml as determined by a most-probable-number method, which exceeds previously reported viable cells / ml by >100-fold. Strain fer1 displayed chemolithotrophic growth with Fe²⁺ in mfer containing 100 mM FeSO₄ or FeCl₂. In the absence of Fe²⁺, heterotrophic growth occurred with one of the following salts (100 mM): ZnSO₄, MnSO₄, MgSO₄, (NH₄) ₂SO₄, or Fe₂(SO₄)₃, and did not occur with (100 mM): ZnCl₂, MnCl₂, MgCl ₂, NH₄Cl, or FeCl₃. Escaping headspace gas from strain fer1 cultures formed a precipitate in a zinc acetate trap. Sulfide was absent in the precipitate but zinc and sulfur were detected. These data demonstrate that SO₄ is required for heterotrophic growth of strain fer1 and may have a role in the global sulfur cycle.