Sulfur-oxidizing Acidithiobacillus Research Articles

Bidirectional effects of sulfur-oxidizer Acidithiobacillus thiooxidans in uranium bioleaching systems with or without sulfur by mixed acidophilic bacteria

Bidirectional effects of sulfur-oxidizer Acidithiobacillus thiooxidans in uranium bioleaching systems with or without sulfur by mixed acidophilic bacteria

Bioleaching and Selective Precipitation for Metal Recovery from Basic Oxygen Furnace Slag

Decreasing ore grades and an increasing consumption of metals has led to a shortage of important primary raw materials. Therefore, the urban mining of different deposits and anthropogenic stocks is of increasing interest. Basic oxygen furnace (BOF) slag is produced in huge quantities with the so-called Linz-Donawitz process and contains up to 5.2, 0.9, 0.1, and 0.07% of Mn, Al, Cr, and V, respectively. In the present study, sulfur-oxidizing Acidithiobacillus thiooxidans and iron- and sulfur-oxidizing Acidithiobacillus ferridurans were applied in batch and stirred tank experiments to investigate the biological extraction of metals from BOF slag. In the batch experiments, up to 96.6, 52.8, 41.6, and 29.3% of Cr, Al, Mn, and V, respectively, were recovered. The stirred tank experiments, with increasing slag concentrations from 10 to 75 g/L, resulted in higher extraction efficiencies for A. ferridurans and lower acid consumption. Selective metal precipitation was performed at pH values ranging between 2.5 and 5.0 to study the recovery of Mn, Al, Cr, and V from the biolixiviant. Selective precipitation of V and Cr was achieved at pH 4.0 from A. thiooxidans biolixiviant, while Fe and V could be selectively recovered from A. ferridurans biolixiviant at pH 3.0. This work revealed the potential of BOF slag as an artificial ore for urban mining and demonstrated that combining bioleaching and selective precipitation is an effective method for sustainable metal recovery.

Simultaneous recovery of valuable metal ions and tailings toxicity reduction using a mixed culture bioleaching process

Lead–zinc sulfide mine tailings without appropriate disposal would cause resource waste and heavy metal pollution in the environment. This study aims to design a novel mixed culture A with higher leaching performance to improve the leaching efficiency of tailings, because mixed culture B consisting of ferrous oxidizer Leptospirillum ferriphilum (L. ferriphilum) and sulfur oxidizer Acidithiobacillus thiooxidans still has a long leaching period. The results showed that mixed culture A containing ferrous/sulfur oxidizers Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans shortened the bioleaching cycle by 30% to achieve the same zinc yield (94.0%) as mixed culture B. Thus, ferrous/sulfur oxidizers offer a competitive advantage over ferrous oxidizer and sulfur oxidizer, respectively, during bacterial combination to leach tailings. The better performance of mixed culture A was verified by its higher content of extracellular polymeric substances and living cells density (30.2 × 107 cells mL−1). Furthermore, data from microbial community succession also revealed that two bacteria could together produce acid in the mixed culture A system to substantially facilitate zinc leaching, while only L. ferriphilum played a role in mixed culture B system. Interestingly, results from toxicity evaluation of bioleached residues indicated that mixed culture A dramatically reduced the potential ecological risk index of tailings from 161.80 to 7.50, transforming tailings from hazardous waste into non-hazardous one. In brief, this study proposes a novel perspective for bacterial combinations to improve tailings bioleaching and reveals that bioleaching can reduce the eco-environmental risk of tailings.

RNA transcript response by an Acidithiobacillus spp. mixed culture reveals adaptations to growth on arsenopyrite.

Biooxidation of gold-bearing refractory mineral ores such as arsenopyrite (FeAsS) in stirred tanks produces solutions containing highly toxic arsenic concentrations. In this study, ferrous iron and inorganic sulfur-oxidizing Acidithiobacillus strain IBUN Ppt12 most similar to Acidithiobacillus ferrianus and inorganic sulfur compound oxidizing Acidithiobacillus sp. IBUNS3 were grown in co-culture during biooxidation of refractory FeAsS. Total RNA was extracted and sequenced from the planktonic cells to reveal genes with different transcript counts involved in the response to FeAsS containing medium. The co-culture's response to arsenic release during biooxidation included the ars operon genes that were independently regulated according to the arsenopyrite concentration. Additionally, increased mRNA transcript counts were identified for transmembrane ion transport proteins, stress response mechanisms, accumulation of inorganic polyphosphates, urea catabolic processes, and tryptophan biosynthesis. Acidithiobacillus spp. RNA transcripts also included those encoding the Rus and PetI proteins involved in ferrous iron oxidation and gene clusters annotated as encoding inorganic sulfur compound metabolism enzymes. Finally, mRNA counts of genes related to DNA methylation, management of oxidative stress, chemotaxis, and motility during biooxidation were decreased compared to cells growing without mineral. The results provide insights into the adaptation of Acidithiobacillus spp. to growth during biooxidation of arsenic-bearing sulfides.

Pyrrhotite Biooxidation by Moderately Thermophilic Acidophilic Microorganisms

The goal of the present work was to study the oxidation of sulfide mineral pyrrhotite by members of microbial groups predominant in biohydrometallurgical processes (mixotrophic iron- and sulfur-oxidizing bacterium Sulfobacillus thermosulfidooxidans strain VKMV 1269T, autotrophic sulfur-oxidizing bacterium Acidithiobacillus caldus strain MBC-1, and heterotrophic iron- and sulfur-oxidizing archaeon Acidiplasma sp. strain MBA-1) to evaluate the role of microorganisms with different physiological properties in the leaching of this mineral. It was shown that pyrrhotite was most actively leached by the sulfur-oxidizing strain Acidithiobacillus caldus MBC-1, as well as by mixed cultures in which this strain was present: S. thermosulfidooxidans VKMV 1269T + A. caldus MBC-1 and Acidiplasma sp. MBA-1 + A. caldus MBC-1. These cultures leached 70, 43, and 60% of pyrrhotite, respectively, after 30 days of the experiment. In experiments with pure cultures S. thermosulfidooxidans VKMV 1269T, Acidiplasma sp. MBA-1 and a mixed culture S. thermosulfidooxidans VKMV 1269T + Acidiplasma sp. MBA-1, the rates of pyrrhotite leaching were significantly lower: 29, 37 and 30%, respectively. An experiment on sulfur biooxidation by pure cultures of the studied microorganisms demonstrated that A. caldus strain MBC-1 was the most active sulfur oxidizer. Thus, it was shown that the bioleaching of pyrrhotite was carried out mainly by sulfur-oxidizing microorganisms, with sulfur biooxidation as the most important process. Active biooxidation of the Fe2+ ion by iron-oxidizing microorganisms did not increase activity of pyrrhotite oxidation, but, on the contrary, led to inhibition of pyrrhotite leaching. Thus, active biooxidation of sulfur, which is formed during the leaching of pyrrhotite, was a factor determining the leaching rate for this sulfide mineral.

Acidithiobacillus ferrianus sp. nov.: an ancestral extremely acidophilic and facultatively anaerobic chemolithoautotroph

Strain MG, isolated from an acidic pond sediment on the island of Milos (Greece), is proposed as a novel species of ferrous iron- and sulfur-oxidizing Acidithiobacillus. Currently, four of the eight validated species of this genus oxidize ferrous iron, and strain MG shares many key characteristics with these four, including the capacities for catalyzing the oxidative dissolution of pyrite and for anaerobic growth via ferric iron respiration. Strain MG also grows aerobically on hydrogen and anaerobically on hydrogen coupled to ferric iron reduction. While the 16S rRNA genes of the iron-oxidizing Acidi-thiobacillus species (and strain MG) are located in a distinct phylogenetic clade and are closely related (98–99% 16S rRNA gene identity), genomic relatedness indexes (ANI/dDDH) revealed strong genomic divergence between strain MG and all sequenced type strains of the taxon, and placed MG as the first cultured representative of an ancestral phylotype of iron oxidizing acidithiobacilli. Strain MG is proposed as a novel species, Acidithiobacillus ferrianus sp. nov. The type strain is MGT (= DSM 107098T = JCM 33084T). Similar strains have been found as isolates or indicated by cloned 16S rRNA genes from several mineral sulfide mine sites.

Phylogeny, Divergent Evolution, and Speciation of Sulfur-Oxidizing Acidithiobacillus Populations

BackgroundHabitats colonized by acidophiles as an ideal physical barrier may induce genetic exchange of microbial members within the common communities, but little is known about how species in extremely acidic environments diverge and evolve.ResultsUsing the acidophilic sulfur-oxidizer Acidithiobacillus as a case study, taxonomic reclassifications of many isolates provides novel insights into their phylogenetic lineage. Whole-genome-based comparisons were attempted to investigate the intra- and inter-species divergence. Recent studies clarified that functional and structural specificities of bacterial strains might provide opportunities for adaptive evolution responding to local environmental conditions. Acidophilic microorganisms play a key role in the acidification of natural waters and thus the formation of extremely acidic environments, and the feedbacks of the latter might confer the distinct evolutionary patterns of Acidithiobacillus spp. Varied horizontal gene transfer events occurred in different bacterial strains, probably resulting in the expansion of Acidithiobacillus genomes. Gene loss as another evolutionary force might cause the adaptive phenotypic diversity. A conceptual model for potential community-dependent evolutionary adaptation was thus proposed to illustrate the observed genome differentiation.ConclusionsCollectively, the findings shed light on the phylogeny and divergent evolution of Acidithiobacillus strains, and provided a useful reference for evolutionary studies of other extremophiles.

Bioleaching potential of bacterial communities in historic mine waste areas

Microbial activity has the potential to alter all cultural heritage in mining and metallurgy, due to metal mobilization by leaching. This communication shows the consequences of the bioleaching ability of two natural enrichments on copper slag samples from a historic ore smelting site in Sangerhausen (Mansfeld, Sudharz, Saxony-Anhalt, Germany). Enrichment cultures gained from mine drainage were dominated by either the iron and sulfur-oxidizing Acidithiobacillus ferrivorans, or by the iron-oxidizing Leptospirillum. During 35 days of bioleaching in media containing copper slag pulp, inoculated with these enrichments, the change in pH and solubilized metal concentrations of the systems were monitored. Both bacterial strains were completely different from each other in their pattern of pH variation and rates of metal solubilization. The maximum removal of Cu (1725 mg/l) and Zn (715 mg/l) from copper slag substrate was achieved with enrichment culture of A. ferrivorans SCUT-1. However, maximum Mn (207 mg/l), Pb (86 mg/l), and Ni (75 mg/l) removal was observed with enrichment culture of Leptospirillum strain YQP-1. Implications for metal mobilization along with alteration of artifacts from not only historic mining areas but also aspects of decontamination and remediation are discussed.

Comparative proteomic analysis of sulfur-oxidizing Acidithiobacillus ferrooxidans CCM 4253 cultures having lost the ability to couple anaerobic elemental sulfur oxidation with ferric iron reduction

In extremely acidic environments, ferric iron can be a thermodynamically favorable electron acceptor during elemental sulfur oxidation by some Acidithiobacillus spp. under anoxic conditions. Quantitative 2D-PAGE proteomic analysis of a resting cell suspension of a sulfur-grown Acidithiobacillus ferrooxidans CCM 4253 subculture that had lost its iron-reducing activity revealed 147 protein spots that were downregulated relative to an iron-reducing resting cell suspension of the antecedent sulfur-oxidizing culture and 111 that were upregulated. Tandem mass spectrometric analysis of strongly downregulated spots identified several physiologically important proteins that apparently play roles in ferrous iron oxidation, including the outer membrane cytochrome Cyc2 and rusticyanin. Other strongly repressed proteins were associated with sulfur metabolism, including heterodisulfide reductase, thiosulfate:quinone oxidoreductase and sulfide:quinone reductase. Transcript-level analyses revealed additional downregulation of other respiratory genes. Components of the iron-oxidizing system thus apparently play central roles in anaerobic sulfur oxidation coupled with ferric iron reduction in the studied microbial strain.

Biogeography of sulfur-oxidizing Acidithiobacillus populations in extremely acidic cave biofilms.

Extremely acidic (pH 0–1.5) Acidithiobacillus-dominated biofilms known as snottites are found in sulfide-rich caves around the world. Given the extreme geochemistry and subsurface location of the biofilms, we hypothesized that snottite Acidithiobacillus populations would be genetically isolated. We therefore investigated biogeographic relationships among snottite Acidithiobacillus spp. separated by geographic distances ranging from meters to 1000s of kilometers. We determined genetic relationships among the populations using techniques with three levels of resolution: (i) 16S rRNA gene sequencing, (ii) 16S–23S intergenic transcribed spacer (ITS) region sequencing and (iii) multi-locus sequencing typing (MLST). We also used metagenomics to compare functional gene characteristics of select populations. Based on 16S rRNA genes, snottites in Italy and Mexico are dominated by different sulfur-oxidizing Acidithiobacillus spp. Based on ITS sequences, Acidithiobacillus thiooxidans strains from different cave systems in Italy are genetically distinct. Based on MLST of isolates from Italy, genetic distance is positively correlated with geographic distance both among and within caves. However, metagenomics revealed that At. thiooxidans populations from different cave systems in Italy have different sulfur oxidation pathways and potentially other significant differences in metabolic capabilities. In light of those genomic differences, we argue that the observed correlation between genetic and geographic distance among snottite Acidithiobacillus populations is partially explained by an evolutionary model in which separate cave systems were stochastically colonized by different ancestral surface populations, which then continued to diverge and adapt in situ.

High-resolution microbial community succession of microbially induced concrete corrosion in working sanitary manholes.

Microbially-induced concrete corrosion in headspaces threatens wastewater infrastructure worldwide. Models for predicting corrosion rates in sewer pipe networks rely largely on information from culture-based investigations. In this study, the succession of microbes associated with corroding concrete was characterized over a one-year monitoring campaign using rRNA sequence-based phylogenetic methods. New concrete specimens were exposed in two highly corrosive manholes (high concentrations of hydrogen sulfide and carbon dioxide gas) on the Colorado Front Range for up to a year. Community succession on corroding surfaces was assessed using Illumina MiSeq sequencing of 16S bacterial rRNA amplicons and Sanger sequencing of 16S universal rRNA clones. Microbial communities associated with corrosion fronts presented distinct succession patterns which converged to markedly low α-diversity levels (< 10 taxa) in conjunction with decreasing pH. The microbial community succession pattern observed in this study agreed with culture-based models that implicate acidophilic sulfur-oxidizer Acidithiobacillus spp. in advanced communities, with two notable exceptions. Early communities exposed to alkaline surface pH presented relatively high α-diversity, including heterotrophic, nitrogen-fixing, and sulfur-oxidizing genera, and one community exposed to neutral surface pH presented a diverse transition community comprised of less than 20% sulfur-oxidizers.

Critical values of the volumetric oxygen transfer coefficient and oxygen concentration that prevent oxygen limitation in ferrous iron and elemental sulfur oxidation by Acidithiobacillus ferrooxidans

Biochemical and biotechnological aspects of aeration conditions in iron- and sulfur-oxidizing Acidithiobacillus ferrooxidans cultures were studied. The critical values of volumetric oxygen transfer coefficient, (kLa)crit, and oxygen concentration, Ccrit, were used to define the conditions necessary for minimum aeration and to eliminate potential oxygen limitation during substrate oxidation by the model bioleaching culture. The Michaelis constants for oxygen were 1.07 and 0.61μmol O2 l−1 for the oxidation of ferrous iron and elemental sulfur, respectively. The Ccrit values, below which oxygen limitation may occur, were 6.250 and 3.125μmol O2 l−1, determined in respirometric experiments for the oxidation of ferrous iron and elemental sulfur, respectively. The rates of iron and sulfur oxidation were also determined at the Ccrit values by measuring the formation of ferric iron and protons in the corresponding cell suspensions. Neither iron nor sulfur oxidation was limited by oxygen at Ccrit. The (kLa)crit values required to maintain oxygen-unlimited oxidation of ferrous iron and elemental sulfur were 7.70 and 4.88h−1, respectively.

Analysis of the microbial community in moderately acidic drainage from the Yanahara pyrite mine in Japan.

Acid rock drainage (ARD) originating from the Yasumi-ishi tunnel near the main tunnel of the Yanahara mine in Japan was characterized to be moderately acidic (pH 4.1) and contained iron at a low concentration (51 mg/L). The composition of the microbial community was determined by sequence analysis of 16S rRNA genes using PCR and denaturing gradient gel electrophoresis. The analysis of the obtained sequences showed their similarity to clones recently detected in other moderately acidic mine drainages. Uncultured bacteria related to Ferrovum- and Gallionella-like clones were dominant in the microbial community. Analyses using specific primers for acidophilic iron- or sulfur-oxidizing bacteria, Acidithiobacillus ferrooxidans, Leptospirillum spp., Acidithiobacillus caldus, Acidithiobacillus thiooxidans, and Sulfobacillus spp. revealed the absence of these bacteria in the microbial community in ARD from the Yasumi-ishi tunnel. Clones affiliated with a member of the order Thermoplasmatales were detected as the dominant archaea in the ARD microbial population.

New Insights into the Biofilm Lifestyle and Metabolism of &lt;i&gt;Acidithiobacillus&lt;/i&gt; Species from Analysis of High Throughput Proteomic Data

Bioleaching is the extraction of metals, such as copper or gold, from sulfidic ores by microorganisms. Their energy for growth is obtained by oxidation of ferrous iron and/or reduced inorganic sulfur compounds. Bacterial attachment to ores increase leaching activities through the formation of a special microenvironment between the bacterium and the metal sulfide surface, filled by extracellular polymeric substances (EPS). Recently, a high-throughput proteomic comparison from biofilm cells attached to pyrite (FeS2) and planktonic cells of the mesophilic iron and/or sulfur oxidizer Acidithiobacillus ferrooxidans ATCC 23270 was done. Several proteins were found to be up-regulated in biofilm cells. Among them, membrane and outer membrane proteins probably involved in osmotic regulation, polysaccharide biosynthesis and protein secretion, as well as proteins probably involved in cofactor metabolism were present. In order to extend our knowledge of the genus Acidithiobacilli, we started a high-throughput proteomic analysis of the sulfur oxidizer Acidithiobacillus caldus ATCC 51756 by comparing cells grown with an insoluble energy substrate such as elemental sulfur (S°) against cells grown on a soluble energy substrate, such as thiosulfate. The results revealed several differences in proteins related to sulfur metabolism, potential EPS biosynthesis pathways as well as membrane and transport functions. In both microorganisms several conserved hypothetical proteins were found. Some of them were also found to be induced in sessile cells, suggesting their potential involvement in biofilm formation. This study will provide new insights into the biology of Acidithiobacilli and will probably help assigning functions to poorly characterized and unknown proteins. Keywords: Biofilm, Proteomics, Acidithiobacilli

Cellular ATP and biomass of attached and planktonic sulfur-oxidizing Acidithiobacillus ferrooxidans

This study demonstrates differences in ATP levels between attached and planktonic cells of Acidithiobacillus ferrooxidans growing with elemental sulfur. A small fraction of 3.7–14.4% of the bacterial cells was attached to the sulfur particles. The highest cell attachment of 14.4% was at the end of the lag phase, decreasing to 3.7% into the latter part of the active growth phase. Therefore, attached cells and their ATP content made a minor contribution to the total culture biomass in the active growth phase. However, the cellular ATP content was 1.01amol per attached cell and 0.34amol per planktonic cell. The significantly (P<0.01) lower ATP content was attributed to sulfur limitation in the planktonic cells. These results suggest that a negligibly small subpopulation may be a link in cooperative interaction whereby sulfur oxidation by attached cells under boundary conditions provides bioavailable substrates to planktonic cells in the population.

Investigation of energy gene expressions and community structures of free and attached acidophilic bacteria in chalcopyrite bioleaching

In order to better understand the bioleaching mechanism, expression of genes involved in energy conservation and community structure of free and attached acidophilic bacteria in chalcopyrite bioleaching were investigated. Using quantitative real-time PCR, we studied the expression of genes involved in energy conservation in free and attached Acidithiobacillus ferrooxidans during bioleaching of chalcopyrite. Sulfur oxidation genes of attached A. ferrooxidans were up-regulated while ferrous iron oxidation genes were down-regulated compared with free A. ferrooxidans in the solution. The up-regulation may be induced by elemental sulfur on the mineral surface. This conclusion was supported by the results of HPLC analysis. Sulfur-oxidizing Acidithiobacillus thiooxidans and ferrous-oxidizing Leptospirillum ferrooxidans were the members of the mixed culture in chalcopyrite bioleaching. Study of the community structure of free and attached bacteria showed that A. thiooxidans dominated the attached bacteria while L. ferrooxidans dominated the free bacteria. With respect to available energy sources during bioleaching of chalcopyrite, sulfur-oxidizers tend to be on the mineral surfaces whereas ferrous iron-oxidizers tend to be suspended in the aqueous phase. Taken together, these results indicate that the main role of attached acidophilic bacteria was to oxidize elemental sulfur and dissolution of chalcopyrite involved chiefly an indirect bioleaching mechanism.

Influence of the sulfur species reactivity on biofilm conformation during pyrite colonization by Acidithiobacillus thiooxidans

Massive pyrite (FeS₂) electrodes were potentiostatically modified by means of variable oxidation pulse to induce formation of diverse surface sulfur species (S(n)²⁻, S⁰). The evolution of reactivity of the resulting surfaces considers transition from passive (e.g., Fe(1-x )S₂) to active sulfur species (e.g., Fe(1-x )S(2-y ), S⁰). Selected modified pyrite surfaces were incubated with cells of sulfur-oxidizing Acidithiobacillus thiooxidans for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the attached cells density and their exopolysaccharides were analyzed by confocal laser scanning microscopy (CLMS) and atomic force microscopy (AFM) on bio-oxidized surfaces; additionally, S(n)²⁻/S⁰ speciation was carried out on bio-oxidized and abiotic pyrite surfaces using Raman spectroscopy. Our results indicate an important correlation between the evolution of S(n)²⁻/S⁰ surface species ratio and biofilm formation. Hence, pyrite surfaces with mainly passive-sulfur species were less colonized by A. thiooxidans as compared to surfaces with active sulfur species. These results provide knowledge that may contribute to establishing interfacial conditions that enhance or delay metal sulfide (MS) dissolution, as a function of the biofilm formed by sulfur-oxidizing bacteria.

Microbial Architecture of Environmental Sulfur Processes: A Novel Syntrophic Sulfur-Metabolizing Consortia

Microbial oxidation of sulfur-rich mining waste materials drives acid mine drainage (AMD) and affects the global sulfur biogeochemical cycle. The generation of AMD is a complex, dynamic process that proceeds via multiple reaction pathways. The role of natural consortia of microbes in AMD generation, however, has received very little attention despite their widespread occurrence in mining environments. Through a combination of geochemical experimentation and modeling, scanning transmission X-ray microscopy, and fluorescent in situ hybridization, we show a novel interdependent metabolic arrangement of two ubiquitous and abundant AMD bacteria: chemoautotrophic sulfur-oxidizing Acidithiobacillus sp. and heterotrophic Acidiphilium sp. Highly reminiscent of anaerobic methane oxidation (AOM) consortia, these bacteria are spatially segregated within a planktonic macrostructure of extracellular polymeric substance in which they syntrophically couple sulfur oxidation and reduction reactions in a mutually beneficial arrangement that regenerates their respective sulfur substrates. As discussed here, the geochemical impacts of microbial metabolism are linked to the consortial organization and development of the pod structure, which affects cell-cell interactions and interactions with the surrounding geochemical microenvironment. If these pods are widespread in mine waters, echoing the now widespread discovery of AOM consortia, then AMD-driven CO(2) atmospheric fluxes from H(2)SO(4) carbonate weathering could be reduced by as much as 26 TgC/yr. This novel sulfur consortial discovery indicates that organized metabolically linked microbial partnerships are likely widespread and more significant in global elemental cycling than previously considered.

Impacts of growth kinetics of sulfur-oxidizing Acidithiobacillus ferrooxidans on kinetic models

The purpose of this study was to evaluate changes in kinetics of growth and elemental sulfur oxidation in Acidithiobacillus ferrooxidans cultures from the point of view of kinetic models of sulfuric acid formation. The values of maximum sulfur oxidation rate (v) and growth yield on sulfur (Y) were determined from data obtained in 86 batch cultures using bioreactors and shakers under the conditions described earlier. Both the constants demonstrated very different values in different cultures of the same strain. No significant correlation between the v and Y values was observed. Two metabolic phases of ATP formation occurred. During the second one, the rate of cell growth did not correlate with the rate of ATP formation. The reasons for the above changes remain unclear. Whether or not the background of the kinetic changes is related to the natural property of sulfur metabolism in the studied strain or other sulfur-oxidizing bacteria remains to be determined. As a result of this, the comparison and prediction of the kinetic constants is uncertain. Traditional kinetic approaches (exponential growth, the Monod equation) could be used for data of growth and sulfur oxidation. However, high variations of kinetic parameters represented substantial limits for the kinetic model application to predict the bioprocess course.

Bioleaching of chromium from tannery sludge by indigenous Acidithiobacillus thiooxidans

Chromium in tannery sludge will cause serious environmental problems and is toxic to organisms. The acidophilic sulfur-oxidizing Acidithiobacillus thiooxidans can leach heavy metals form urban and industrial wastes. This study examined the ability of an indigenous sulfur-oxidizing A. thiooxidans to leach chromium from tannery sludge. The results showed that the pH of sludge mixture inoculated with the indigenous A. thiooxidans decreased to around 2.0 after 4 days. After 6 days incubation in shaking flasks at 30 °C and 160 rpm, up to 99% of chromium was solubilized from tannery sludge. When treated in a 2-l bubble column bioreactor for 5 days at 30 °C and aeration of 0.5 vvm, 99.7% of chromium was leached from tannery sludge. The results demonstrated that chromium in tannery sludge can be efficiently leached by the indigenous A. thiooxidans.