Alternative electron transfer pathways in iron-metabolising bacteria

Gomez Perez, Laura (2018) Alternative electron transfer pathways in iron-metabolising bacteria. Doctoral thesis, University of East Anglia.

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    Abstract

    Ferric iron (Fe3+) can be used as a terminal electron acceptor by iron-reducing microorganisms to facilitate cellular respiration under anoxic conditions. In contrast, ferrous iron (Fe2+) is used as an electron donor by iron-oxidising microorganisms. The presence of dissimilatory pathways in iron metabolisers maintain bioavailable iron in the environment for other organisms. Redox reactions between gram-negative bacteria and iron usually occur through an extracellular electron transport (EET) pathway that allows electrons to cross from the inner membrane to the extracellular environment or vice versa. The study of the redox pathway has been thoroughly studied in the iron reducer Shewanella oneidensis, however, there is little information about the metabolic pathways used by other iron metabolisers. In this thesis, the environmental isolates Acinetobacter and Citrobacter have been described as novel iron reducing bacteria by using a combination of techniques including ferrozine assays, cytochrome identification methods and transcriptomic analysis. Results in this thesis suggest that Acinetobacter (previously described as a strict aerobic microorganism) in fact is capable of respiring using iron when oxygen is not available. In contrast, Citrobacter’s iron reduction pathway seems to involve fermentative processes. These results point out that extracellular electron transport is not the only mechanism in dissimilatory iron metabolism. Moreover, these results suggest that anaerobic environments could be a reservoir for pathogenic strains of Acinetobacter, as it has been shown that this species do not require oxygen to survive. In addition to the study of new iron reducers, an overexpression system has been developed to study proteins involved in metal oxidation pathways without the need of culturing the notoriously slow-growing iron oxidising bacteria. The genes cyc2 and cyc2PV-1, which encode outer membranes cytochromes from Acidithiobacillus ferrooxidans and Mariprofundus ferrooxydans respectively, have been transformed into the iron reducer Shewanella oneidensis for protein expression optimization. The optimization of this process offers great possibility for the future study and applications of metal oxidation pathways.

    Item Type: Thesis (Doctoral)
    Faculty \ School: Faculty of Science > School of Biological Sciences
    Depositing User: Jackie Webb
    Date Deposited: 12 Feb 2019 11:39
    Last Modified: 12 Feb 2019 11:39
    URI: https://ueaeprints.uea.ac.uk/id/eprint/69911
    DOI:

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