Complete Genome Sequences of Extremely Thermoacidophilic Metal-Mobilizing Type Strain Members of the Archaeal Family Sulfolobaceae, Acidianus brierleyi DSM-1651, Acidianus sulfidivorans DSM-18786, and Metallosphaera hakonensis DSM-7519

The family Sulfolobaceae contains extremely thermoacidophilic archaea that are found in terrestrial environments. Here, we report three closed genomes from two currently defined genera within the family, namely, Acidianus brierleyi DSM-1651T, Acidianus sulfidivorans DSM-18786T, and Metallosphaera hakonensis DSM-7519T.

Bioleaching of Low-Grade Chalcopyrite Ore by the Thermophilic Archaean Acidianus brierleyi

The thermophilic archaean, Acidianus brierleyi, was examined for its feasibility to bioleach copper from a low-grade chalcopyrite ore (1.15 % copper, 20.4 % iron and 2.63 wt% sulfur) at 65°C and pH 1.8-2.5. The chalcopyrite leaching was markedly accelerated in the presence of A. brierleyi, and an extremely high 80% leaching of copper in the low-grade ore (25-38 μm particles) was achieved in 14 days in a batch stirred reactor. By comparison, the leaching of iron was very slow and only a slight 5 % iron was leached in 14 days in the presence or absence of A. brierleyi. In other words, A. brierleyi selectively leached chalcopyrite while magnetite leaching by A. brierleyi was negligible. Moreover, bioleaching of the low-grade ore (53-75 μm particles) yielded 55% copper recovery after 20 days of operation in a column reactor. The good results for the copper bioleaching in the column reactor are very similar to those in the stirred reactor. These results lead to the conclusion that the thermophile bioleaching with A. brierleyi is attractive as an economical and environmentally friendly process for good copper extraction from low-grade chalcopyrite ore.

Optimization of Bioscorodite Crystallization for Treatment of As(III)-Bearing Wastewaters

Arsenic (As) is a major impurity contaminated in metal refinery wastewaters. To immobilize As ions, we have previously reported microbial scorodite (FeAsO4·2H2O) crystallization using the thermo-acidophilic iron-oxidizing archaeon, Acidianus brierleyi. In order to extend the applicable range of As (III)-bearing metal refinery wastewaters (especially for dilute As (III) concentrations of 250–1500 ppm), this study investigated the effect of several factors possibly affecting the bioscorodite crystallization efficiency; (i) [Fe (II)]ini/[As (III)]ini molar ratio at different target As (III) concentrations, (ii) initial pH, and (iii) seed scorodite with different morphologies. The [Fe (II)]ini/[As (III)]ini molar ratio strongly affected the bioscorodite crystallization efficiency at each target As (III) concentration. Whilst the [Fe (II)]ini/[As (III)]ini molar ratio of 1.4 was most effective at 500–1500 ppm As (III), the optimal molar ratios for treating more dilute concentrations (< 500 ppm) were shown to be relatively higher. However, further increasing the [Fe (II)]ini/[As (III)]ini molar ratio resulted in formation of unwanted potassium jarosite (KFe3(OH)6(SO4)2) together with scorodite. Lowering the initial pH from 1.5 to 1.2 resulted in earlier scorodite nucleation, but lesser overall As immobilization. Feeding chemical-and bio-scorodite seed crystals differently affected the reaction speed and the stability of newly-precipitated bioscorodite. The TCLP test indicated that scorodite formed on bioscorodite seeds is more stable than that formed on chemically-synthesized scorodite seeds.

Effect of Cu(II) on Bio-Scorodite Crystallization Using Acidianus brierleyi

The effect of different concentrations of Cu (II) on microbial scorodite (FeAsO4⋅2H2O) formation was investigated by using thermo-acidophilic iron-oxidizing archaeon, Acidianus brierleyi. In the presence of 8-16 mM Cu (II) microbial Fe (II) oxidation and cell growth was only marginal. Its As (III) oxidation ability was especially severely inhibited by the presence of Cu (II), consequently disabling scorodite formation. However, when scorodite seed crystals were fed, Ac. brierleyi readily oxidized Fe (II) and As (III) even in the presence of 8.0 mM Cu (II), forming crystalline scorodite within 24 days in shake flasks. All Cu (II) remained in the solution phase during scorodite crystallization, with or without the presence of seed crystals. Increasing the seed crystal concentration (from 0.015 to 0.15%) slightly improved the As immobilization (from 96 to 98%). This study demonstrated that scorodite can be crystallized from the model As (III)-bearing wastewater containing Cu (II).