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Iron and sulfur utilisation patterns in chemolithotrophic cultures

Shiers, Denis (2012) Iron and sulfur utilisation patterns in chemolithotrophic cultures. PhD thesis, Murdoch University.

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In this study, the growth and behaviour of chemolithotrophic organisms in the presence of both ferrous and tetrathionate ions was investigated. Given the impact of chemolithotrophic metabolic activity upon the chemistry and leaching of mineral sulfide systems, investigations were conducted to determine the effects of solution variables on substrate utilisation.

A set of eight organisms, capable of oxidising ferrous ions or reduced sulfur compounds, were adapted to ferrous or tetrathionate ions. These cell lines were cultured in media containing 2.5 mM of tetrathionate, with either high or low concentrations of ferrous ions present. Sb.xthermosulfidooxidans and M. hakonensis grew in a diauxic growth pattern utilising ferrous ions preferentially, irrespective of adaptive history or ferrous concentration. At. ferrooxidans, Sb. acidophilus, Sb.xsibiricus, Sb. thermotolerans, A.xbrierleyi and S. metallicus exhibited simultaneous substrate utilisation and a single phase of growth under at least one of the four conditions tested. Preferential utilisation of tetrathionate was not observed under any of the four conditions tested. Planktonic cell numbers were not consistently proportional to the total quantity of the reduced substrate(s) oxidised.

Reduced sulfur species were detected during batch culture growth of At. caldus on tetrathionate. Formation of elemental sulfur, thiosulfate, sulfite, penta- and hexathionate were consistent with the enzymatic hydrolysis of tetrathionate and subsequent chemical reactions. Growth yields were comparatively low with an average value of 3.53 g(dry wt.) mol(S4O6)-1. However, a significant quantity of reduced organic material was detected dissolved in solution. Yield data obtained from this study was compared with other reports and analysed using a thermodynamic framework derived from studies of heterotrophic growth. This analysis indicated that the conserved substrate had a sulfur(IV) atom oxidised to sulfur(VI).

The addition of nitrate significantly modified substrate oxidation patterns in a growth medium containing ferrous and tetrathionate ions. Ferrous ion oxidation processes were inhibited to a greater extent than tetrathionate utilisation. Tetrathionate-adapted cultures of Sb. acidophilus and Sb. sibiricus demonstrated preferential oxidation of tetrathionate at nitrate concentrations of 20–40 mM. Iron-adapted cultures of M.xhakonensis preferentially oxidised ferrous ions in the presence of nitrate at all concentrations where growth was observed. Responses of other test species varied, depending on the nitrate concentration and adaptive history of the organism.

Nitrate was added to control the redox potential of the solution in cultures bioleaching chalcopyrite. Redox potentials were not controlled at 30 and 45 °C. Copper extraction was equal to, or less than that seen in cultures without nitrate present. The addition of nitrate to cultures at 60 °C maintained the redox potential between 430–460 mV (Ag/AgCl). Copper extraction in these systems was increased compared with cultures where nitrate was absent.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Chemical and Mathematical Science
Supervisor: Ralph, David
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