Rusticyanin gene expression of Acidithiobacillus ferrooxidans ATCC 33020 in sulfur- and in ferrous iron media

Among the bioleaching microorganisms, Acidithiobacillus ferrooxidans is one of the most studied. The bioleaching and bioremediation properties of this obligate chemolithoautotroph originate from its energetic metabolism. Even though several electron-transfer proteins have been identified, there is no convincing argument to tell in which respiratory chain these proteins are involved. Rusticyanin is the A. ferrooxidans redox protein which has been the most extensively studied. This periplasmic blue copper protein is widely considered to play an important role in ferrous oxidation mainly because of its higher concentration in iron-grown cells compared to sulfur-grown cells. To gain more insight on which conditions rusticyanin is synthesized, we have studied the rus gene expression all along the growth in iron- and sulfur-supplemented media at the translational level by immunodetection and at the transcriptional level by Northern blot analyses and quantitative RT-PCR experiments. In the A. ferrooxidans ATCC 33020 strain, rusticyanin was present in ferrous iron-grown cells throughout all the growth phases. In sulfur-grown cells. rusticyanin was present only during the exponential phase, but to a lower level than in iron conditions, and disappeared at the stationary phase. In cultures switched from sulfur- to iron-medium, there was a correlation between iron oxidation and the rusticyanin level. Strikingly, the de novo synthesis of rusticyanin was observed in sulfur-grown cells. All these data agree with a control on rusticyanin level in the cells depending on the electron donor present in the medium and on the growth phase in sulfur-grown cells. Furthermore, they are consistent with the involvement of rusticyanin in iron oxidation. (C) 2003 Elsevier B.V. All rights reserved.