Biochemical and electrochemical characterization of redox protein candidates of the iron oxidation in the acidophilic iron oxidizer “Ferrovum” sp. PN-J47-F6

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Aerobic iron oxidizing organisms coupling ferrous iron oxidation to the reduction of oxygen cope with life at the thermodynamic limit due to the extremely low redox potential difference between the electron donor (ferrous/ferric iron) and acceptor couple (oxygen/water). Since external pH also effects the redox potential of the electron donor and acceptor couple and, thereby, the energy yield of the electron transfer process, it has been postulated that the biochemical properties of redox proteins involved in iron oxidation are also effected by the external pH of the habitat. However, biochemical studies on redox proteins of iron oxidizers are limited to few model organisms (Acidithiobacillus ferrooxidans, Ferroplasma acidiphilum). Nevertheless, omics-based research allowed the prediction of electron transfer chains in several prokaryotes. Among Betaproteobacteria there are both acidophilic iron oxidizers, such as “Ferrovum” spp. and neutrophilic iron oxidizers. In comparison to model acidophiles members of the genus “Ferrovum” are more moderate acidophiles. A model of the iron oxidation in “Ferrovum” spp. was inferred by genome analysis and extended based on transcriptome data. Intriguingly, redox proteins of the predicted iron oxidation model share more similarities with those of neutrophilic iron oxidizers belonging to the Beta- and Zetaproteobacteria than with those of other acidophiles.Hence, “Ferrovum” spp. present a unique model to investigate whether biochemical properties of iron oxidation proteins have adapted to the lower external pH. Therefore, the proposed project aims to investigate the phylogeny of the protein candidates of the iron oxidation model and to characterize their biochemical properties. Aim (i) will be approached bioinformatically: Dendrograms of these redox proteins will be calculated and then be compared to dendrograms based on taxonomic markers (i.e. 16S rRNA gene sequence). Aim (ii) will be approached at two levels. First, selected soluble protein candidates of “Ferrovum” sp. PN-J47-F6 will be produced heterologously for biochemical and electrochemical characterization in order to identify their redox centers and to determine their mid-point potential. Protein-protein interaction studies are planned to elucidate the proposed electron transfer chain of the iron oxidation model. The second level involves biochemical and electrochemical characterization of wild type proteins in membrane fractions of “Ferrovum” sp. PN-J47-F6. Therefore, biochemical properties of the recombinant proteins are intended to be used as reference. The proposed study will amend our current knowledge on microbial iron oxidation by providing the first biochemical data on redox proteins involved in iron oxidation in a moderate acidophile. This data may allow valuable insights into how evolution of this energy conserving process has been influenced by external pH of the habitat.