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Analysis of differential protein expression during growth states of Ferroplasma strains and insights into electron transport for iron oxidation

Mark Dopson^1,

¹ School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
² Centre for Ecology, Evolution and Conservation, University of East Anglia, Norwich NR4 7TJ, UK

Correspondence
Philip Bond
phil.bond{at}uea.ac.uk

To investigate the metabolic biochemistry of iron-oxidizing extreme acidophiles, a proteomic analysis of chemomixotrophic and chemo-organotrophic growth, as well as protein expression in the absence of organic carbon, was carried out in Ferroplasma species. Electron transport chain inhibitor studies, spectrophotometric analysis and proteomic results suggest that oxidation of ferrous iron may be mediated by the blue copper-haem protein sulfocyanin and the derived electron passes to a cbb₃ terminal electron acceptor. Despite previous suggestions of a putative carbon dioxide fixation pathway, no up-regulation of proteins typically associated with carbon dioxide fixation was evident during incubation in the absence of organic carbon. Although a lack of known carbon dioxide fixation proteins does not constitute proof, the results suggest that these strains are not autotrophic. Proteins putatively involved in central metabolic pathways, a probable sugar permease and flavoproteins were up-regulated during chemo-organotrophic growth in comparison to the protein complement during chemomixotrophic growth. These results reflect a higher energy demand to be derived from the organic carbon during chemo-organotrophic growth. Proteins with suggested function as central metabolic enzymes were expressed at higher levels during chemomixotrophic growth by Ferroplasma acidiphilum Y^T compared to ‘Ferroplasma acidarmanus’ Fer1. This study addresses some of the biochemical and bioenergetic questions fundamental for survival of these organisms in extreme acid-leaching environments.

Supplementary tables with details of the proteins induced under various conditions are available with the online version of this paper.

Present address: Molecular Biology, Umeå University, S-90187 Umeå, Sweden.

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