Iron bioleaching and polymers accumulation by an extreme acidophilic bacterium.

In many European regions, both local metallic and non-metallic raw materials are poorly exploited due to their low quality and the lack of technologies to increase their economic value. In this context, the development of low cost and eco-friendly approaches, such as bioleaching of metal impurities, is crucial. The acidophilic strain Acidiphilium sp. SJH reduces Fe(III) to Fe(II) by coupling the oxidation of an organic substrate to the reduction of Fe(III) and can therefore be applied in the bioleaching of iron impurities from non-metallic raw materials. In this work, the physiology of Acidiphilium sp. SJH and the reduction of iron impurities from quartz sand and its derivatives have been studied during growth on media supplemented with various carbon sources and under different oxygenation conditions, highlighting that cell physiology and iron reduction are tightly coupled. Although the organism is known to be aerobic, maximum bioleaching performance was obtained by cultures cultivated until the exponential phase of growth under oxygen limitation. Among carbon sources, glucose has been shown to support faster biomass growth, while galactose allowed highest bioleaching. Moreover, Acidiphilium sp. SJH cells can synthesise and accumulate Poly-ß-hydroxybutyrate (PHB) during the process, a polymer with relevant application in biotechnology. In summary, this work gives an insight into the physiology of Acidiphilium sp. SJH, able to use different carbon sources and to synthesise a technologically relevant polymer (PHB), while removing metals from sand without the need to introduce modifications in the process set up.

The significance of pH in dictating the relative toxicities of chloride and copper to acidophilic bacteria.

The ability of acidophilic bacteria to grow in the presence of elevated concentrations of cationic transition metals, though varying between species, has long been recognized to be far greater than that of most neutrophiles. Conversely, their sensitivity to both inorganic and organic anions, with the notable exception of sulfate, has generally been considered to be far more pronounced. We have compared the tolerance of different species of mineral-oxidizing Acidithiobacillus and Sulfobacillus, and the heterotrophic iron-reducer Acidiphilium cryptum, to copper and chloride when grown on ferrous iron, hydrogen or glucose as electron donors at pH values between 2.0 and 3.0. While tolerance of copper varied greatly between species, these were invariably far greater at pH 2.0 than at pH 3.0, while their tolerance of chloride showed the opposite pattern. The combination of copper and chloride in liquid media appeared to be far more toxic than when these elements were present alone, which was thought to be due to the formation of copper-chloride complexes. The results of this study bring new insights into the understanding of the physiological behaviour of metal-mobilising acidophilic bacteria, and have generic significance for the prospects of bioleaching copper ores and concentrates in saline and brackish waters.

Enhancing As(V) adsorption and passivation using biologically formed nano-sized FeS coatings on limestone: Implications for acid mine drainage treatment and neutralization.

The iron-reducing bacterium Acidiphilium cryputum JF-5 and a sulfate reducing bacterium (SRB) collected and purified from the mine drainage of a copper mine in the northwest of Sichuan Province, China, were used to biologically synthesize nano-sized FeS-coated limestone to remove As(V) from solution. The adsorption efficiency of As(V) is improved from 6.64 µg/g with limestone alone to 187 µg/g with the FeS coated limestone in both batch and column experiments. The hydraulic conductivity of the columns are also improved by the presence of the nano-sized FeS coatings, but the solution neutralization performance of the limestone can be reduced by passivation by gypsum and Fe(III) precipitates. Calculations for FeS-coated limestone dissolution experiments show that the process can be described as nCa.sol = At1/2 - nCa,gyp. The results suggest that FeS-coated limestone may be an effective medium for remediating As(V)-bearing solutions such as acid mine drainage in systems such as Permeable Reactive Barriers.

Use of an acidophilic yeast strain to enable the growth of leaching bacteria on solid media.

In this study, a Candida digboiensis strain was isolated from a heap leaching plant in Zambia and used in double-layer agar plate to efficiently isolate and purify leaching bacteria. Unlike Acidiphilium sp., the yeast strain was tetrathionate tolerant and could metabolize a great range of organic compounds including organic acids. These properties allowed the yeast strain to enable and fasten the growth of iron and sulfur oxidizers on double-layer agar plate. The isolates were identified as Acidithiobacillus ferrooxidans FOX1, Leptospirillun ferriphilum BN, and Acidithiobacillus thiooxidans ZMB. These three leaching bacteria were inhibited by organic acids such as acetic and propionic acids; however, their activities were enhanced by Candida digboiensis NB under dissolved organic matter stress.

The co-culture of Acidithiobacillus ferrooxidans and Acidiphilium acidophilum enhances the growth, iron oxidation, and CO2 fixation.

Although the synergetic interactions between chemolithoautotroph Acidithiobacillus ferrooxidans and heterotroph Acidiphilium acidophilum have drawn a share of attention, the influence of Aph. acidophilum on growth and metabolic functions of At. ferrooxidans is still unknown on transcriptional level. To assess this influence, a co-culture composed by At. ferrooxidans and Aph. acidophilum was successfully acclimated in this study. Depending on the growth dynamics, At. ferrooxidans in co-culture had 2 days longer exponential phase and 5 times more cell number than that in pure culture. The ferrous iron concentration in culture medium and the expression of iron oxidation-related genes revealed that the energy acquisition of At. ferrooxidans in co-culture was more efficient than that in pure culture. Besides, the analysis of CO2 fixation-related genes in At. ferrooxidans indicated that the second copy of RuBisCO-encoding genes cbbLS-2 and the positive regulator-encoding gene cbbR were up-regulated in co-culture system. All of these results verified that Aph. acidophilum could heterotrophically grow with At. ferrooxidans and promote the growth of it. By means of activating iron oxidation-related genes and the second set of cbbLS genes in At. ferrooxidans, the Aph. acidophilum facilitated the iron oxidation and CO2 fixation by At. ferrooxidans.

Mechanism of adsorption of ferric iron by extracellular polymeric substances (EPS) from a bacterium Acidiphilium sp.

The aim of this study was to assess the sorption of Fe(III) by extracellular polymeric substances (EPS) of the Acidiphilium 3.2Sup(5) bacterium, which has promising properties for use in microbial fuel cells (MFC). The EPS of A. 3.2Sup(5) was extracted using EDTA. The sorption isotherms were determined using aliquots of purified EPS. The exosubstances loaded with metal were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction spectroscopy (XRD) and Fourier transform infrared spectroscopy (FTIR). The sorption uptake approaches to 536.1 +/- 26.6 mg Fe(III) (g EPS)(-1) at an initial ferric concentration of 2.0 g l(-1). The sorption of Fe(III) by EPS can be fitted to the Freundlich model. The sorption process produces hydrated iron (III) oxalate [Fe(OH)(C2O4) x 2H2O] by a reversible reaction (log K = 1.06 +/- 0.16), indicating that a shift in the sorption of the cation can be easily achieved. Know the magnitude and form of iron sorption by EPS in MFC can foresee the potential impact on the metabolism of iron-reducing and iron-oxidazing bacteria and, therefore, on the feasibility of the system.

The role of Acidithiobacillus ferrooxidans in alleviating the inhibitory effect of thiosulfate on the growth of acidophilic Acidiphilium species isolated from acid mine drainage samples from Garubathan, India.

Several acidophilic chemolithoautotrophic and heterotrophic strains were isolated from acid mine drainage samples from Garubathan, West Bengal, India. The strains, chemolithoautotrophic DK6.1 and heterotrophic DKAP1.1, used in this study were assigned to the species Acidithiobacillus ferrooxidans and Acidiphilium cryptum, respectively. Unamended filtered and subsequently autoclaved elemental sulfur spent medium of A. ferrooxidans was used as the medium to study heterotrophic growth of A. cryptum DKAP1.1. While characterizing the heterotrophic strain, an inhibitory effect of thiosulfate on A. cryptum DKAP1.1 was identified. The lethality of thiosulfate broth was directly related to the concentration of thiosulfate in the medium. Nonviability of A. cryptum DKAP1.1 in the presence of thiosulfate was alleviated by A. ferrooxidans DK6.1 in co-culture. Microbiological data on a positive growth effect for A. ferrooxidans DK6.1 caused by co-culturing in solid media in the presence of A. cryptum DKAP1.1 is also presented.

Preferential use of an anode as an electron acceptor by an acidophilic bacterium in the presence of oxygen.

Several anaerobic metal-reducing bacteria have been shown to be able to donate electrons directly to an electrode. This property is of great interest for microbial fuel cell development. To date, microbial fuel cell design requires avoiding O(2) diffusion from the cathodic compartment to the sensitive anodic compartment. Here, we show that Acidiphilium sp. strain 3.2 Sup 5 cells that were isolated from an extreme acidic environment are able to colonize graphite felt electrodes. These bacterial electrodes were able to produce high-density electrocatalytic currents, up to 3 A/m(2) at a poised potential of +0.15 V (compared to the value for the reference standard calomel electrode) in the absence of redox mediators, by oxidizing glucose even at saturating air concentrations and very low pHs.

[Isolation and characterization of Acidiphilium strain teng-A and its metabolism of fe (III) during pure- and mixed cultivation].

An acidophilic, aerobic and chemoheterotrophic bacterial strain Teng-A was isolated from acidic environmental samples collected at sulfidic hot springs of Tengchong County, Yunnan Province, China. Cells of strain Teng-A was rod-shaped (0.6-0.8 microm x 1.0 - 1.5 microm), Gram-negative, motile with flagella. Strain Teng-A grew well at temperature of 29-33 degrees C and at pH of 3.0-4.0. It used a wide variety of organic compounds for growth, but did not use ferrous iron, elemental sulfur, thiosulfate and tetrathionate as the sole energy source. Its G + C content was determined to be 69.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequence demonstrated that it was closely related to species of Acidiphilium. Under anoxic conditions, the strain Teng-A reduced Fe(III) to Fe(II) with glucose or hy drogen as electron donor (reduction rate is 11.56 mg/L day and 15.34 mg/L x day, respectively). Metabolisms/Oxidation of ferrous iron by Acidithiobacillus ferrooxidans LJ-1 and Leptospirilum ferriphilum LJ-2, in the presence and absence of strain Teng-A were studied. When incubated with strain Teng-A, the oxidation rates of Fe(II) was slightly decreased at the first 3 days (0.44 g/L x day and 0.4 g/L x day respectively) compared to pure culture of At ferrooxidans and L. ferriphilum, but all Fe(II) was completely oxidized after 5 days. It was found that the morphologies of precipitates of Fe (III) produced during pure and mixed cultivation were different. The potential application of Acidiphilium in bioleaching and its potential role during formation of precipitated ores were discussed.

Iron respiration by Acidiphilium cryptum at pH 5.

The growth of acidophilic iron respiring bacteria at pH > 4.5 may be a key to the transition from acidic to circumneutral conditions that would occur during restoration of acid mine drainage sites. Flasks containing Acidiphilium cryptum ATCC 33463 were incubated initially under aerobic conditions in liquid medium containing Fe(2)(SO(4))(3) and glucose at an initial pH of 5. Significant iron respiration was observed after flasks were sealed to prevent oxygenation; at the same time, medium pH increased from 4.5 to 6. No soluble Fe(III) was detected throughout the experiments, consistent with pH conditions, indicating that bacteria were able to respire using precipitated ferric iron species. In addition, the concentration of soluble Fe(2+) reached a plateau, even though iron respiration appeared to continue, possibly due to precipitation of mixed Fe (II)/Fe(III)-oxide as magnetite. Results suggest that A. cryptum has a wide range of pH tolerance, which may enable it to play a role in controlling acid generation by means of establishing growth conditions favorable to neutrophilic bacteria such as sulfate reduction.