Apparent redundancy of electron transfer pathways via bc1 complexes and terminal oxidases in the extremophilic chemolithoautotrophic Acidithiobacillus ferrooxidans

• Published in: Biochimica et biophysica acta. Bioenergetics 2004-06, Vol.1656 (2), p.114-126
• Main Authors: Brasseur, G, Levican, G, Bonnefoy, V, Holmes, D, Jedlicki, E, Lemesle-Meunier, D
• Format: Article
• Language: English
• Subjects: Acidithiobacillus ferrooxidans; Acidophile; bc1 complex; Electron transfer chain; Iron and sulfur oxidation; Terminal oxidase
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2004.02.008

Acidithiobacillus ferrooxidans is an acidophilic chemolithoautotrophic bacterium that can grow in the presence of either the weak reductant Fe 2+, or reducing sulfur compounds that provide more energy for growth than Fe 2+. We have previously shown that the uphill electron transfer pathway between Fe 2+ and NAD + involved a bc 1 complex that functions only in the reverse direction [J. Bacteriol. 182, (2000) 3602]. In the present work, we demonstrate both the existence of a bc 1 complex functioning in the forward direction, expressed when the cells are grown on sulfur, and the presence of two terminal oxidases, a bd and a ba 3 type oxidase expressed more in sulfur than in iron-grown cells, besides the cytochrome aa 3 that was found to be expressed only in iron-grown cells. Sulfur-grown cells exhibit a branching point for electron flow at the level of the quinol pool leading on the one hand to a bd type oxidase, and on the other hand to a bc 1→ ba 3 pathway. We have also demonstrated the presence in the genome of transcriptionally active genes potentially encoding the subunits of a bo 3 type oxidase. A scheme for the electron transfer chains has been established that shows the existence of multiple respiratory routes to a single electron acceptor O 2. Possible reasons for these apparently redundant pathways are discussed.