title: Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1-1.3.
abstract: The extreme acid conditions required for scorodite (FeAsO₄·2H₂O) biomineralization (pH below 1.3) are suboptimal for growth of most thermoacidophilic Archaea. With the objective to develop a continuous process suitable for biomineral production, this research focuses on growth kinetics of thermoacidophilic Archaea at low pH conditions. Ferrous iron oxidation rates were determined in batch-cultures at pH 1.3 and a temperature of 75°C for Acidianus sulfidivorans, Metallosphaera prunea and a mixed Sulfolobus culture. Ferrous iron and CO₂ in air were added as sole energy and carbon source. The highest growth rate (0.066 h⁻¹) was found with the mixed Sulfolobus culture. Therefore, this culture was selected for further experiments. Growth was not stimulated by increase of the CO₂ concentration or by addition of sulphur as an additional energy source. In a CSTR operated at the suboptimal pH of 1.1, the maximum specific growth rate of the mixed culture was 0.022 h⁻¹, with ferrous iron oxidation rates of 1.5 g L⁻¹ d⁻¹. Compared to pH 1.3, growth rates were strongly reduced but the ferrous iron oxidation rate remained unaffected. Influent ferrous iron concentrations above 6 g L⁻¹ caused instability of Fe²⁺ oxidation, probably due to product (Fe³⁺) inhibition. Ferric-containing, nano-sized precipitates of K-jarosite were found on the cell surface. Continuous cultivation stimulated the formation of an exopolysaccharide-like substance. This indicates that biofilm formation may provide a means of biomass retention. Our findings showed that stable continuous cultivation of a mixed iron-oxidizing culture is feasible at the extreme conditions required for continuous biomineral formation.
authors.affiliation: Sub-department of Environmental Technology, Wageningen University, Bornse Weilanden 9, P.O. Box 17, 6708 WG, Wageningen, the Netherlands. paulaa.gonzalezcontreras@wur.nl
authors.forename: Paula
authors.initials: P
authors.lastname: Gonzalez-Contreras
authors.forename: Jan
authors.initials: J
authors.lastname: Weijma
authors.forename: Cees J N
authors.initials: CJ
authors.lastname: Buisman
mesh_terms: D001152:Arsenicals / Q000378:metabolism; D019149:Bioreactors; D001709:Biotechnology / Q000379:methods; D003470:Culture Media / Q000737:chemistry; D005290:Ferric Compounds / Q000378:metabolism; D005296:Ferrous Compounds / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction; D013431:Sulfates / Q000378:metabolism; D016942:Sulfolobales / Q000254:growth & development* / Q000378:metabolism*; D013696:Temperature
chemical_list: D001152:Arsenicals; D003470:Culture Media; D005290:Ferric Compounds; D005296:Ferrous Compounds; D013431:Sulfates; C492331:jarosite; C548094:scorodite; D007501:Iron