Changes in Acidithiobacillus ferrooxidans ability to reduce ferric iron by elemental sulfur

Ferric iron may act as a thermodynamically favourable electron acceptor during elemental sulfur oxidation by Acidithiobacillus ferrooxidans in extremely acidic anoxic
environments. A loss of anaerobic ferric iron reduction ability has been observed in ferrous iron-grown A. ferrooxidans CCM 4253 after aerobic passaging on elemental sulfur. In this study, iron-oxidising cells aerobically adapted from ferrous iron to elemental sulfur were still able to anaerobically reduce ferric iron, however, following aerobic passage on elemental sulfur it could not. Preliminary quantitative proteomic analysis of whole cell lysates of the passage that lost anaerobic ferric iron-reducing activity resulted in 150 repressed protein spots in comparison with the antecedent culture, which retained the activity. Identification of selected protein spots by tandem mass spectrometry revealed physiologically important proteins including rusticyanin and outer-membrane cytochrome Cyc2, which are involved in iron oxidation. Other proteins were associated with sulfur metabolism such as sulfide-quinone reductase and proteins encoded by the thiosulfate dehydrogenase and heterodisulfide reductase complex operons. Furthermore, proteomic analysis identified proteins directly related to anaerobiosis. The results indicate the importance of iron-oxidising system components for anaerobic sulfur oxidation in the studied microbial strain.