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.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-011-3460-7) contains supplementary material, which is available to authorized users.

Continuous bioscorodite crystallization in CSTRs for arsenic removal and disposal

“…Only on day 180, the ferrous iron oxidation temporally decreased as a late result of the increased arsenate concentration, which was also reflected in a decrease of the redox potential. The cell count was in the order of 1e4$10 6 cells mL À1 at several time of operation, which is similar to the cell count in previous runs (Gonzalez-Contreras et al, 2012). The low cell count coincided with the low protein value of 2 mg protein L À1 (measured in CSTR-2).…”

“…Iron oxidation kinetics of the mixed culture at the suboptimal growth conditions suitable for bioscorodite crystallization were previously studied (Gonzalez-Contreras et al, 2012). The growth medium for the thermo-acidophiles contained: 1 g L À1 (NH 4 ) 2 SO 4 , 0.1 g L À1 KCl, 0.5 g L À1 MgSO 4 $7H 2 O, and 0.5 g L À1 K 2 HPO 4 as described by Plumb et al (2002).…”

Archaeal and bacterial diversity in acidic to circumneutral hot springs in the Philippines

“…Acidic hot springs are considered extreme environments, yet they contain a diverse array of thermoacidophilic microorganisms capable of surviving and functioning under such conditions (Brock et al ., ; Brock, ; Stetter, ; Rothschild & Mancinelli, ). Multiple investigations have shown that thermoacidophiles in terrestrial geothermal features are of great importance because of their potential implications for early life on Earth (Konhauser et al ., ) and extraterrestrial biology (Cavicchioli, ), as well as applications in biotechnology (Edwards et al ., ) and bioremediation (Norris et al ., ; Gonzalez‐Contreras et al ., ). Over the last decade, several culture‐independent studies have investigated microbial communities in acidic hot springs, such as those in Tengchong, China (Hou et al ., ), Iceland (Kvist et al ., ), Yellowstone National Park (YNP) (Jackson et al ., ; Inskeep et al ., ; Kozubal et al ., , b; Macur et al ., ) and Lassen Volcanic National Park (Siering et al ., ; Wilson et al ., ) in the United States.…”

Arsenic immobilization as crystalline scorodite by gas-diffusion electrocrystallization

“…Scorodite has also been precipitated at 95 °C by the oxidation of ferrous ions and oxygen gas in the presence of As 5+ , with concentrations as high as 0.7 M in sulfuric acid solution. 1 Biogenic scorodite has been made at 72 °C between 0.5 and 2.5 g As 5+ L −1 ; in this case, thermophilic archaea were utilized to microbiallyoxidize Fe 2+ to Fe 3+ , 13 though higher concentrations of arsenic were avoided due to arsenic inhibition of microorganisms. Moreover, the costs for aeration with the biomass and nutrient addition are elevated.…”