Assessment of biofilm changes and concentration-depth profiles during arsenopyrite oxidation by Acidithiobacillus thiooxidans

Biofilm formation and evolution are key factors to consider to better understand the kinetics of arsenopyrite biooxidation. Chemical and surface analyses were carried out using Raman spectroscopy, scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), glow discharge spectroscopy (GDS), and protein analysis (i.e., quantification) in order to evaluate the formation of intermediate secondary compounds and any significant changes arising in the biofilm structure of Acidithiobacillus thiooxidans during a 120-h period of biooxidation. Results show that the biofilm first evolves from a low cell density structure (1 to 12 h) into a formation of microcolonies (24 to 120 h) and then finally becomes enclosed by a secondary compound matrix that includes pyrite (FeS₂)-like, S _n^2-/S⁰, and As₂S₃ compounds, as shown by Raman and SEM-EDS. GDS analyses (concentration-depth profiles, i.e., 12 h) indicate significant differences for depth speciation between abiotic control and biooxidized surfaces, thus providing a quantitative assessment of surface-bulk changes across samples (i.e. reactivity and /or structure-activity relationship). Respectively, quantitative protein analyses and CLSM analyses suggest variations in the type of extracellular protein expressed and changes in the biofilm structure from hydrophilic (i.e., exopolysaccharides) to hydrophobic (i.e., lipids) due to arsenopyrite and cell interactions during the 120-h period of biooxidation. We suggest feasible environmental and industrial implications for arsenopyrite biooxidation based on the findings of this study.

The effect of oxygen supply on the dual growth kinetics of Acidithiobacillus thiooxidans under acidic conditions for biogas desulfurization

In this study, to simulate a biogas desulfurization process, a modified Monod-Gompertz kinetic model incorporating a dissolved oxygen (DO) effect was proposed for a sulfur-oxidizing bacterial (SOB) strain, Acidithiobacillus thiooxidans, under extremely acidic conditions of pH 2. The kinetic model was calibrated and validated using experimental data obtained from a bubble-column bioreactor. The SOB strain was effective for H₂S degradation, but the H₂S removal efficiency dropped rapidly at DO concentrations less than 2.0 mg/L. A low H₂S loading was effectively treated with oxygen supplied in a range of 2%–6%, but a H₂S guideline of 10 ppm could not be met, even with an oxygen supply greater than 6%, when the H₂S loading was high at a short gas retention time of 1 min and a H₂S inlet concentration of 5000 ppm. The oxygen supply should be increased in the aerobic desulfurization to meet the H₂S guideline; however, the excess oxygen above the optimum was not effective because of the decline in oxygen efficiency. The model estimation indicated that the maximum H₂S removal rate was approximately 400 ppm/%-O₂ at the influent oxygen concentration of 4.9% under the given condition. The kinetic model with a low DO threshold for the interacting substrates was a useful tool to simulate the effect of the oxygen supply on the H₂S removal and to determine the optimal oxygen concentration.

Growth Inhibition by Tungsten in the Sulfur-Oxidizing BacteriumAcidithiobacillus thiooxidans

Growth of five strains of sulfur-oxidizing bacteria Acidithiobacillus thiooxidans, including strain NB1-3, was inhibited completely by 50 microM of sodium tungstate (Na(2)WO(4)). When the cells of NB1-3 were incubated in 0.1 M beta-alanine-SO(4)(2-) buffer (pH 3.0) with 100 microM Na(2)WO(4) for 1 h, the amount of tungsten bound to the cells was 33 microg/mg protein. Approximately 10 times more tungsten was bound to the cells at pH 3.0 than at pH 7.0. The tungsten binding to NB1-3 cells was inhibited by oxyanions such as sodium molybdenum and ammonium vanadate. The activities of enzymes involved in elemental sulfur oxidation of NB1-3 cells such as sulfur oxidase, sulfur dioxygenase, and sulfite oxidase were strongly inhibited by Na(2)WO(4). These results indicate that tungsten binds to NB1-3 cells and inhibits the sulfur oxidation enzyme system of the cells, and as a result, inhibits cell growth. When portland cement bars supplemented with 0.075% metal nickel and with 0.075% metal nickel and 0.075% calcium tungstate were exposed to the atmosphere of a sewage treatment plant containing 28 ppm of H(2)S for 2 years, the weight loss of the portland cement bar with metal nickel and calcium tungstate was much lower than the cement bar containing 0.075% metal nickel.

Inhibition of microbial concrete corrosion by Acidithiobacillus thiooxidans with functionalised zeolite-A coating

The inhibition of the corrosive action of Acidithiobacillus thiooxidans on concrete specimens coated by functionalised zeolite-A containing 14% zinc and 5% silver by weight was studied. Uncoated concrete specimens, epoxy-coated concrete specimens (EP), and functionalised zeolite-A coated concrete specimens with epoxy to zeolite weight ratios of 3:1 (Z1), 2:2 (Z2) and 1:3 (Z3) were studied. Specimens were characterised by x-ray powder diffraction and field emission scanning electron microscopy for the identification of corrosion products and morphological changes. Biomass growth at the conclusion of the 32-day experiments was 4, 179 and 193 mg volatile suspended solids g(-1) sulphur for the uncoated, EP and Z1 specimens, whereas that of Z2 and Z3 were negligible. In the uncoated, EP and Z1 specimens, sulphate production rates were 0.83, 9.1 and 8.8 mM SO(4)(2-) day(-1) and the specific growth rates, mu, were 0.14, 0.57 and 0.47 day(-1), respectively. The corresponding values for Z2 and Z3 were negligible due to their bacterial inhibition characteristics.

Adaptive changes of chemolithoautotrophic acidophilic sulfur-oxidizing bacteria during growth in sewage sludge

A chemolithoauthotrophic, acidophilic, sulfur-oxidizing strain was isolated from sewage sludge and identified as Acidithiobacillus thiooxidans. The morphology and physiology of the isolate grown in mineral medium or sterilized sewage sludge were investigated. Morphological and ultrastructural differences between cells grown in mineral medium and sewage sludge were clearly visible. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed some changes in the protein expression profiles in the periplasmic fraction as well as a lower level of cytochromes. Adaptation of A. thiooxidans to sewage sludge was not only a physiological process but also included genetic changes. Restriction fragment length polymorphism analysis using pulsed field gel electrophoresis showed structural changes in chromosomal DNA of such bacteria. Most of the restriction fragments were highly conserved and shared by strains grown under different conditions. Cultivation in mineral medium did, however, lead to the appearance of an additional restriction fragment. In combination, the obtained results provide evidence of adaptive responses by A. thioxidans during growth in sewage sludge and confirm that this bacteria can be useful in biotechnologies of heavy metal bioleaching from different environments polluted with hazardous compounds.

Succession of sulfur-oxidizing bacteria in the microbial community on corroding concrete in sewer systems

Microbially induced concrete corrosion (MICC) in sewer systems has been a serious problem for a long time. A better understanding of the succession of microbial community members responsible for the production of sulfuric acid is essential for the efficient control of MICC. In this study, the succession of sulfur-oxidizing bacteria (SOB) in the bacterial community on corroding concrete in a sewer system in situ was investigated over 1 year by culture-independent 16S rRNA gene-based molecular techniques. Results revealed that at least six phylotypes of SOB species were involved in the MICC process, and the predominant SOB species shifted in the following order: Thiothrix sp., Thiobacillus plumbophilus, Thiomonas intermedia, Halothiobacillus neapolitanus, Acidiphilium acidophilum, and Acidithiobacillus thiooxidans. A. thiooxidans, a hyperacidophilic SOB, was the most dominant (accounting for 70% of EUB338-mixed probe-hybridized cells) in the heavily corroded concrete after 1 year. This succession of SOB species could be dependent on the pH of the concrete surface as well as on trophic properties (e.g., autotrophic or mixotrophic) and on the ability of the SOB to utilize different sulfur compounds (e.g., H2S, S0, and S2O3(2-)). In addition, diverse heterotrophic bacterial species (e.g., halo-tolerant, neutrophilic, and acidophilic bacteria) were associated with these SOB. The microbial succession of these microorganisms was involved in the colonization of the concrete and the production of sulfuric acid. Furthermore, the vertical distribution of microbial community members revealed that A. thiooxidans was the most dominant throughout the heavily corroded concrete (gypsum) layer and that A. thiooxidans was most abundant at the highest surface (1.5-mm) layer and decreased logarithmically with depth because of oxygen and H2S transport limitations. This suggested that the production of sulfuric acid by A. thiooxidans occurred mainly on the concrete surface and the sulfuric acid produced penetrated through the corroded concrete layer and reacted with the sound concrete below.

[Bacterial leaching of manganese ores]

Leaching of various types of ores, containing 12-30% manganese, by the thiobacterium Acidithiobacillus ferrooxidans was studied. Leaching of reduced ores (manganocalcite and manganiferous limestone) was mediated mainly by degradation of manganiferous minerals (by sulfuric acid produced in the course of bacterial oxidation of pyrite or sulfur). Bacterial treatment of the ores for 144 and 192 h allowed solubilization of 96-98% of manganese. Inoculation of bacteria into pulp with pyrite increased the rate of leaching of oxide ore (psilomelane) by 37%, and the degree of its extraction within 180 h increased from 80 to 97%.

[Dependence of the genotypic characteristics of Acidithiobacillus ferrooxidans on the physical, chemical, and electrophysical properties of pyrites]

Comparison of Acidithiobacillus ferrooxidans strains TFV-1 and TFBk with respect to their capacity to oxidize pyrite 1, with hole-type (p-type) conductivity, or pyrite 2, with an electron-type (n-type) conductivity, showed that, at a pulp density of 1%, both before and after its adaptation to the pyrites, strain TFBk, isolated from a substrate with a more complex mineral composition, grew faster and oxidized the pyrites of both conductivity types more efficiently than strain TFV-1, which was isolated from a mineralogically simple ore. At a pulp density of 3-5%, the oxidation of pyrite 1 by strain TFV-1 and both of the pyrites by strain TFBk began only after an artificial increase in Eh to 600 mV. If the pulp density was increased gradually, strain TFBk could oxidize the pyrites at its higher values than strain TFV-1, with the rate of pyrite 2 oxidation being higher than that of pyrite 1. During chemical oxidation of both of the pyrites, an increase was observed in the absolute values of the coefficients of thermoelectromotive force (KTEMF); during bacterial-chemical oxidation, the KTEMF of pyrite 1 changed insignificantly, whereas the KTEMF of pyrite 2 decreased.

Identification of IS elements in Acidithiobacillus ferrooxidans strains grown in a medium with ferrous iron or adapted to elemental sulfur

IS elements were identified in the genomes of five Acidithiobacillus ferrooxidans strains isolated from various media. IST2 elements were revealed in all the strains grown in a medium with ferrous iron, ISAfe1 elements were detected in four strains (TFBk, TFL-2, TFV-1 and TFO). Three strains (TFV-1, TFN-d and TFO) were found to contain IS elements, approximately 600 bp long. These were named preliminary as ISAfe600. Partial sequencing of the 5'- and 3'-terminal nucleotide stretches of an ISAfe1 element in TFBk and TFL-2 strains and complete sequencing of the ISAfe1 element in the TFBk strain has revealed nucleotide substitutions as compared to the prototype, i.e., the ISAfe1 element of an ATCC 19859 strain. Partial sequencing of the 5'- and 3'-terminal nucleotide stretches of the IST2 elements in TFO, TFBk and TFL-2 strains has shown numerous nucleotide substitutions when compared to the IST2 element of an ATCC 19859 strain. Complete sequencing of the IST2 element in the TFBk strain has revealed: the divergence between the IST2 elements in the TFBk strain and the prototype was 21.2%. Southern hybridization of EcoRI fragments of the chromosomal DNA from five A. ferrooxidans strains grown in a medium with ferrous iron using an internal region of ISAfe1, a full-length ISAfe1 or a full-length IST2 as probes has shown them to differ in the number of copies of IS elements and their localization on the chromosomes. Adaptation to elemental sulfur in A. ferrooxidans strains caused changes in the number, intensity and localization of hybridization bands. The authors discuss the role of IS elements in the adaptation of A. ferrooxidans to the new energy substrate.

Treatment of H2S using a horizontal biotrickling filter based on biological activated carbon: reactor setup and performance evaluation

Biological treatment is an emerging and prevalent technology for treating off-gases from wastewater treatment plants. The most commonly reported odorous compound in off-gases is hydrogen sulfide (H(2)S), which has a very low odor threshold. A self-designed, bench-scale, cross-flow horizontal biotrickling filter (HBF) operated with bacteria immobilized activated carbon (termed biological activated carbon-BAC), was applied for the treatment of H(2)S. A mixed culture of sulfide-oxidizing bacteria dominated by Acidithiobacillus thiooxidans acclimated from activated sludge was used as bacterial seed and the biofilm was developed by culturing the bacteria in the presence of carbon pellets in mineral medium. HBF performance was evaluated systematically over approximately 120 days, depending on a series of changing factors including inlet H(2)S concentration, gas retention time (GRT), pH of recirculation solution, upset and recovery, sulfate accumulation, pressure drop, gas-liquid ratio, and shock loading. The biotrickling filter system can operate at high efficiency from the first day of operation. At a volumetric loading of 900 m(3) m(-3) h(-1) (at 92 ppmv H(2)S inlet concentration), the BAC exhibited maximum elimination capacity (113 g H(2)S/m(-3) h(-1)) and a removal efficiency of 96% was observed. If the inlet concentration was kept at around 20 ppmv, high H(2)S removal (over 98%) was achieved at a GRT of 4 s, a value comparable with those currently reported for biotrickling filters. The bacterial population in the acidic biofilter demonstrated capacity for removal of H(2)S over a broad pH range (pH 1-7). A preliminary investigation into the different effects of bacterial biodegradation and carbon adsorption on system performance was also conducted. This study shows the HBF to be a feasible and economic alternative to physical and chemical treatments for the removal of H(2)S.

The effects of metabolites from the indigenous Acidithiobacillus thiooxidans and temperature on the bioleaching of cadmium from soil

The effect of metabolites from the indigenous Acidithiobacillus thiooxidans and temperature on the bioleaching of cadmium from soil was investigated in the present study. Bioleaching was found to be more effective than chemical leaching of cadmium. The metabolite, mainly sulfuric acid, which was shown to be growth-associated in the exponential phase, plays a major role in bioleaching. The maximum amount of cadmium leached was obtained after 8 days of precultivation when cells were directly involved in the leaching process. It indicates that cells in the exponential growth phase exhibit higher activity toward bioleaching. In contrast, the maximum amount of cadmium leached and the maximum initial rate for bioleaching were reached after 16 days of precultivation when only metabolites were involved in the bioleaching process. It implies that higher sulfuric acid concentration results in higher leaching efficiency. In addition, higher temperature leads to higher leaching efficiency. The optimal operation condition for bioleaching was determined to be a two-stage process: The first stage involves the precultivation of the indigenous A. thiooxidans at 30 degrees C for 8 days followed by 20 minutes of centrifugation to discard cells. The second stage involves the bioleaching with the subsequent supernatant at 50 degrees C.

A new method using a bacterium for dissolution of urinary stones

PURPOSE

A bacterium, Thiobacillus thiooxidans, oxidizes inorganic sulfur compounds to sulfuric acid to obtain energy for growth. We examined dissolution of urinary stones by the bacteria and studied optimal conditions for the dissolution in human urine.

METHODS

Thiobacillus thiooxidans (IFO No. 13 701) was purchased from Hakko Kenkyujyo, Co., Osaka, Japan. The bacteria were grown stationary for 7 days at 30 degrees C in medium. The pH of the medium was changed from pH 4.82 to 1.95 for 28 days. Growth of the bacteria was also examined in human urine by addition of different amounts of sodium thiosulfite. The dissolution of human urinary stones was examined in the bladder of Wistar rat containing the bacteria (1 x 10(8)) for 7 days. 20 ml of 5 % sodium thiosulfite were injected intraperitoneally once a day. Histological changes of urinary tracts and blood test were also examined. As a control, two rats were examined in the same methods without the bacteria.

RESULTS

The number of bacteria was increased in human urine depending on the concentration of sodium thiosulfite. Among different kinds of urinary stones, calcium phosphate stone was most dissolved, 78 % reduction of dry weight in the rat bladder. Calcium oxalate, uric acid and magnesium phosphate stones were not well dissolved. But the stone weights in the control rats were increased twice. Slight inflammation was found in the rat bladder. There were no abnormal findings in the blood test.

CONCLUSIONS

Thiobacillus thiooxidans can be used for dissolution of urinary stones. This new technique may be useful for dissolution of fragments after ESWL and crystals covered by a urinary stent. Optimal conditions and safety methods should be developed for clinical use.

Monitoring of bio-oxidation process of ferrous ion by using piezoelectric impedance analysis

A new method of monitoring the bio-oxidation process of ferrous ion in the presence of Thiobacillus ferroxidans was proposed by piezoelectric impedance analysis. The time courses of the responses of impedance parameters for a quartz crystal in a culture system were simultaneously obtained and discussed. It was found that the frequency shift response originates mainly from the adsorption of bacterial metabolites on the surface of gold electrode. Experiments also examined the effect of culture temperature on the bio-oxidation process. Combined with the growth situation of the bacterium, an impedance response model reflecting the process was established. By fitting Delta f vs. time curves toward the proposed model, we obtained and discussed the bacterial growth parameters. The results showed that the proposed method could provide real time and multidimensional information to monitoring of the bio-oxidation process.

Characterization of arsenopyrite oxidizing Thiobacillus. Tolerance to arsenite, arsenate, ferrous and ferric iron

Two strains of Thiobacillus, T. ferrooxidans and T. thiooxidans, have been isolated from a bacterial inoculum cultivated during a one-year period in a 1001 continuous laboratory pilot for treatment of an arsenopyrite/pyrite concentrate. The optimum pH for the growth of both strains has been found to be between 1.7 and 2.5. Because of the high metal toxicity in bioleach pulps, the tolerance of T. ferrooxidans and T. thiooxidans with respect to iron and arsenic has been studied. The growth of both strains is inhibited with 10 g/l of ferric ion, 5 g/l of arsenite and 40 g/l of arsenate. 20 g/l of ferrous iron is toxic to T. ferrooxidans but 30 g/l is necessary to impede the growth of T. thiooxidans.

Pyruvate inhibition of the carbon dioxide fixation of the strict chemolithotroph Thiobacillus thiooxidans

A flow-through dialysis system used to decrease the concentrations of toxic organic materials excreted by Thiobacillus thiooxidans permitted an improved efficiency of carbon dioxide fixation when compared with cells taken from the usual shaken culture. The additions of various concentrations of pyruvic acid and succinic acid inhibited growth significantly. Pyruvate at a concentration of 5 X 10(-3) M completely inhibited the respiration of resting cells oxidizing sulfur. The toxicity of pyruvic acid was found to be permanent as evidenced by the inability to obtain satisfactory oxidation rates after washing the exposed cells twice in buffer. Both pyruvate (10(-3) M) and succinate (10(-3) M) inhibited carbon dioxide fixation by 84%.

Relationship between growth and metabolic activity in the strict chemolithotroph, Thiobacillus thiooxidans

The metabolic activity of Thiobacillus thiooxidans was found to decrease rapidly as stationary phase was approached. Keeping the culture at constant pH (4.0) and supplementation with CO2 did not effect the decrease in metabolic activity although growth was increased. The respiration rate of cells obtained from stationary phase was negligible. No growth was obtained when the pH was adjusted to pH 6.0. Measurement of pyruvic acid, an inhibitor of metabolic activity, showed that it reached only about 1.0 × 10−5 M during the early stages of growth and then decreased during exponential growth.

Degradation of oil shale by sulfur-oxidizing bacteria

Approximately 40% of oil shale can be solubilized by the action of sulfur-oxidizing bacteria. Thiobacillus thiooxidans and Thiobacillus concretivorous are equally effective in solubilization. Continuous leaching experiments show that this process can be completed within 14 days. The growth of Thiobacillus and the production of acid were measured under several conditions. Almost all of the CaMg(CO(3))(2) was removed by this process, leaving a complex of silica and kerogen that could be burned as low-energy fuel. The silica-kerogen complex had not yet been biologically degraded.

Heterotrophic nature of the cell-free protein-synthesizing system from the strict chemolithotroph, Thiobacillus thiooxidans

A cell-free protein-synthesizing system prepared from the strict chemolithotroph, Thiobacillus thiooxidans, was similar to that of heterotrophs. The poly-U directed system had a temperature optimum of 37 C, but in the presence of spermidine (3 mM) the optimum shifted to 45 C. Although growth of the chemolithotroph occurs only in acid conditions, the pH optimum for the cell-free system was pH 7.2. The endogenous-directed activity in the presence or absence of spermidine was maximal at pH 7.8. Spermidine had a stimulatory effect; however, this effect was dependent on the magnesium and tris(hydroxymethyl)aminomethane (Tris) concentrations. At low Tris concentrations (10 mM), spermidine (3 to 5 mM) could completely replace magnesium. When the Tris concentration was increased (50 mM), spermidine could not replace magnesium. Supernatant and ribosomal fractions from T. thiooxidans were exchanged with those of Bacillus thuringiensis and Escherichia coli, and the ribosomal fraction from the chemolithotroph gave good to moderate stimulation when exchanged with the supernatant from the heterotrophs. On the other hand, the supernatant from T. thiooxidans gave good stimulation when mixed with ribosomes from B. thuringiensis but poor activity with ribosomes from E. coli. Both supernatant and ribosomal fractions prepared from stationary phase extracts of T. thiooxidans were inactive in the cell-free system.

Effect of supplementary aeration on the growth of Thiobacillus thiooxidans in shaken cultures

The growth rate of shaken cultures of the strict autotroph, Thiobacillus thiooxidans, usually very slow, has been increased about threefold by increasing the level of aeration. The cell yield has also been improved somewhat by this procedure. CO2 enriched air does not enhance growth further.

Ecology of sulfur-oxidizing bacteria in hot acid soils

Hot acid soils in Yellowstone National Park are rich in elemental sulfur and harbor extensive populations of sulfur-oxidizing bacteria. Thiobacillus thiooxidans is found at temperatures below 55 C, and at temperatures from 55 to 85 C Sulfolobus acidocaldarius is present. The distribution of these bacteria as a function of temperature was measured by a most-probable-number dilution method, and their activity in situ was assessed by use of a new technique permitting measurement of (14)CO(2) fixation. From these data it is concluded that sulfur-oxidizing bacteria are responsible for production of sulfuric acid in these acidic thermal habitats. Physical and chemical parameters of this unusual soil habitat were also measured and are described.

Phosphoenolpyruvate carboxylase of Thiobacillus thiooxidans. Kinetic and metabolic control properties

Phosphoenolpyruvate (PEP) carboxylase (orthophosphate:oxalacetate carboxy-lyase (phosphorylating), EC 4.1.1.31) was purified 19-fold from Thiobacillus thiooxidans. The level of enzyme activity was dependent on culture age. No enzyme activity could be obtained from frozen cells.The pH optimum of the enzyme was determined to be around 8.0. Apparent Michaelis constants were determined for the substrates:phosphoenolpyruvate (1.4, 1.5 mM), bicarbonate (0.4, 1.1 mM), and magnesium (1.1, 0.8 mM) at pH 7.0 and 8.0, respectively. Acetyl-CoA was found to be a powerful activator of this enzyme, with the degree of activation increasing with decreasing pH. The concentration of acetyl-CoA to obtain half-maximal activation, however, remained fairly constant and low, namely 1.2 and 1.0 μM at pH 7.0 and 8.0, respectively. L-Aspartate and L-malate were strong inhibitors of enzyme activity. In the presence of aspartate at pH 7.0 the double reciprocal activity plots for PEP became nonlinear, a characteristic of negative cooperativity. These plots became linear with the addition of acetyl-CoA with aspartate now acting as a noncompetitive inhibitor with respect to PEP. At pH 8.0, the same plots were linear with aspartate acting as a competitive inhibitor of PEP. All the other effectors of PEP carboxylase from Salmonella typhimurium and Escherichia coli were found to be ineffective towards the enzyme from T. thiooxidans.