Anaerobic iron respiration of Thiobacillus ferrooxidans and its electron transfer protein

摘要

Primary respiration forms on early earth are considered to be anaerobic sulfur or Fe(III) reduction. The reduction is found in hyperthermophilic archaebacteria that are the most closely related to the last common ancestor of modern life. One of physiological principles of the respiration in Archaea is to support chemolithoautotrophy which is also considered to be ancient character. If anaerobic respiration on inorganic substances is ancestral metabolism for chemolithoautotrophs, the reduction capacities may be conserved even in present aerobic chemolithoautotrophs. Here we report that anaerobic respiration is found as energy taking system for chemolithoautotrophic growth in the evolved modern aerobic bacterium. Thiobacillus ferrooxidans can grow chemolithoautotrophically by anaerobic reduction of Fe(Ⅲ) by H_2. Anaerobic respiration allowed the bacterium to synthesize significant amount of 28 kDa of red color protein as soluble and acid-stable form. This soluble protein was purified to electrophoretic homogeneity and its absorbance represented a typical spectrum of c-type cytochrome. The reduced cytochrome was immediately oxidized by addition of excess Fe(Ⅲ) and the Fe(Ⅲ) was reduced to Fe(II). Anaerobic Fe(Ⅲ) respiration related to c-type cytochrome may be one of primary respiration forms for chemolithoautotrophic character.