The hyperthermophilic archaeon Pyrococcus furiosus utilizes environmental iron sulfide cluster complexes as an iron...

Iron is an essential nutrient for almost all known organisms, but in aerobic, neutral pH environments, it is present primarily as precipitated oxyhydroxide minerals. In contrast, in anaerobic environments, iron can exist in its ferrous form (Fe²⁺) and remain soluble. In sulfide-rich, anaerobic environments, Fe²⁺ and sulfide react to form iron sulfide cluster complexes of the form Fe_xS_x (FeS_aq), which further condense to form the mineral mackinawite, which itself is partly soluble. However, the ability of microorganisms to utilize iron sulfide as an iron source is not known. Here, we show that the anaerobic, hyperthermophilic archaeon Pyrococcus furiosus can directly assimilate the iron in dissolved iron sulfide cluster complexes (FeS_aq) without further dissolution to Fe²⁺. Growth is only inhibited in the presence of a Fe²⁺-specific chelator. The FeS_aq that is utilized can be formed either by reaction of chelated Fe²⁺ with sulfide or dissolved from mackinawite. Pyrococcus furiosus can utilize FeS_aq larger than 3.5 kDa, or Fe₄₀S₄₀, and may actively aid in the dissolution of mackinawite to the assimilated FeS_aq. A model for iron sulfide assimilation from an insoluble mineral is proposed.