Towards determining details of anaerobic growth coupled to ferric iron reduction by the acidophilic archaeon 'Ferroplasma acidarmanus' Fer1

Elucidation of the different growth states of Ferroplasma species is crucial in understanding the cycling of iron in acid leaching sites. Therefore, a proteomic and biochemical study of anaerobic growth in 'Ferroplasma acidarmanus' Fer1 has been carried out. Anaerobic growth in Ferroplasma spp. occurred by coupling oxidation of organic carbon with the reduction of Fe³⁺; but sulfate, nitrate, sulfite, thiosulfate, and arsenate were not utilized as electron acceptors. Rates of Fe³⁺ reduction were similar to other acidophilic chemoorganotrophs. Analysis of the 'F. acidarmanus' Fer1 proteome by 2-dimensional polyacrylamide gel electrophoresis revealed ten key proteins linked with central metabolic pathways >=4 fold up-regulated during anaerobic growth. These included proteins putatively identified as associated with the reductive tricarboxylic acid pathway used for anaerobic energy production, and others including a putative flavoprotein involved in electron transport. Inhibition of anaerobic growth and Fe³⁺ reduction by inhibitors suggests the involvement of electron transport in Fe³⁺ reduction. This study has increased the knowledge of anaerobic growth in this biotechnologically and environmentally important acidophilic archaeon.