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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 (FeAsO?·2H?O) 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 CO? 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 CO? 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.

SUBMITTER: Gonzalez-Contreras P

PROVIDER: S-EPMC3264884 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1-1.3.

Gonzalez-Contreras Paula P Weijma Jan J Buisman Cees J N CJ

Applied microbiology and biotechnology 20110713 3

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 ...[more]

PMID: 21751006

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Project description:The exploration of novel hosts with the ability to assimilate formic acid, a C1 substrate that can be produced from renewable electrons and CO2, is of great relevance for developing novel and sustainable biomanufacturing platforms. Formatotrophs can use formic acid or formate as a carbon and/or reducing power source. Formatotrophy has typically been studied in neutrophilic microorganisms because formic acid toxicity increases in acidic environments below the pKa of 3.75 (25°C). Because of this toxicity challenge, utilization of formic acid as either a carbon or energy source has been largely unexplored in thermoacidophiles, species that possess the ability to produce a variety of metabolites and enzymes of high biotechnological relevance. Here we investigate the capacity of several thermoacidophilic archaea species from the Sulfolobales order to tolerate and metabolize formic acid. Metallosphaera prunae, Sulfolobus metallicus and Sulfolobus acidocaldarium were found to metabolize and grow with 1-2 mM of formic acid in batch cultivations. Formic acid was co-utilized by this species alongside physiological electron donors, including ferrous iron. To enhance formic acid utilization while maintaining aqueous concentrations below the toxicity threshold, we developed a bioreactor culturing method based on a sequential formic acid feeding strategy. By dosing small amounts of formic acid sequentially and feeding H2 as co-substrate, M. prunae could utilize a total of 16.3 mM of formic acid and grow to higher cell densities than when H2 was supplied as a sole electron donor. These results demonstrate the viability of culturing thermoacidophilic species with formic acid as an auxiliary substrate in bioreactors to obtain higher cell densities than those yielded by conventional autotrophic conditions. Our work underscores the significance of formic acid metabolism in extreme habitats and holds promise for biotechnological applications in the realm of sustainable energy production and environmental remediation.

Dataset Information

Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1-1.3.

Publications

Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1-1.3.

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