Search Results (70)

Soils heavily contaminated with potentially toxic elements (PTEs) pose substantial risks to the environment and human health. However, conventional remediation methods are often plagued by high energy consumption and the potential for secondary pollution. To address this challenge, this study developed a synergistic system combining acidophilic bacteria with a Fe-modified anode, aiming to enhance the remediation of PTEs in such contaminated soils. This system integrates the following three core components: the catalytic function of Fe₃O₄–graphene-oxide (Fe₃O₄–GO) nanocomposites, the acclimation of microbial communities, and the optimization of process parameters—specifically, applied electric current, pH, and oxidation–reduction potential (ORP). Experimental treatments were designed to assess the individual and combined effects of three key factors: bacterial inoculation, the Fe-modified anode, and the addition of Fe₃O₄–GO. The results revealed that the integrated synergistic system effectively reduced the soil pH from 2.9 to 2.0 and maintained the ORP at approximately 600 mV. For PTE removal, the system achieved efficiencies of 89% for Zn, 85.89% for Cu, 66.3% for Pb, 77.89% for Cd, and 40.63% for Cr, respectively. In contrast, control groups lacking bacteria, applied current, or Fe₃O₄–GO exhibited significantly lower metal removal efficiencies. Notably, the bacteria-free treatment led to a more than 50% reduction in Cr removal. Additionally, the group with an unmodified anode only achieved 1/3 to 1/2 of the removal efficiencies observed in the full synergistic system; this discrepancy is likely attributed to reduced electron transfer efficiency and compromised microbial adhesion on the anode surface. These findings demonstrate that the coupling of electrochemical enhancement, acidophilic microbial activity, and Fe₃O₄–GO catalysis constitutes an effective and energy-efficient approach for remediating soils contaminated with high concentrations of PTEs while simultaneously minimizing the risk of secondary pollution. Full article

Extremely acidophilic iron- and sulfur-oxidizing bacteria and archaea are used in the processing of different sulfide ores and concentrates (biohydrometallurgical technologies); therefore, studying their metabolic pathways and regulation is an urgent task. Thus, the goal of this work was to compare differential gene expression in the thermoacidophilic archaeal strain, representative of the genus Acidiplasma, a predominant microbial group in bioleach reactors, during growth in the presence of ferrous iron and elemental sulfur as well as pyrite and arsenopyrite, which are the most widespread sulfide minerals, and to obtain novel data on the mechanisms of interaction of microorganisms and sulfide minerals. Transcriptomic analysis revealed metabolic pathways involved in ferrous iron and sulfur oxidation (key processes in sulfide mineral oxidation) and determined their expression dependence on different substrates. It was shown that the blue copper protein sulfocyanin may play an important role in both iron and sulfur oxidation, while sulfur oxidation also involves genes encoding well-known proteins for reduced inorganic sulfur compounds (RISC), sulfur oxygenase reductase (SOR), and thiosulfate quinone oxidoreductase (TQO). The results obtained in the present study may be used in further work to improve biohydrometallurgical technologies. Full article

Chloride ions can enhance the bioleaching of copper minerals, yet most biomining microorganisms are highly sensitive to chloride and cannot survive or colonize mineral surfaces in saline environments. Chloride tolerance varies among acidophilic iron-oxidizing bacteria, but the concentrations at which they remain active are generally too low to permit the industrial use of seawater. Therefore, identifying highly chloride-tolerant leaching microorganisms and studying their bioleaching potential in chloride-containing systems is of utmost importance. This study investigated chloride tolerance and adaptability of bacteria from different genera, with a focus on Sulfobacillus thermosulfidooxidans subsp. asporogenes 41, a moderately thermophilic strain that can oxidize both Fe (II) and reduced inorganic sulfur compounds (RISCs). This dual activity makes it advantageous for bioleaching by facilitating sulfur removal, generating acidity, and preventing mineral passivation. Comparative experiments on the bioleaching of pyrite and chalcopyrite demonstrated that adaptation to 0.3 M NaCl enhanced the chloride tolerance of S. thermosulfidooxidans subsp. asporogenes 41. The adapted strain exhibited significantly improved copper extraction under saline conditions compared with the native culture. Maximum copper recovery was achieved at 0.4 M NaCl, highlighting the potential of chloride-adapted moderate thermophiles for biomining applications in saline environments. In contrast the minimal inhibitory concentration for Acidithiobacillud ferrooxidans Dr was 0.005 M (causing 41.2% inhibition), while Leptospirillum ferriphilum CC was unaffected by lower concentrations (0.01–0.02 M) and only showed severe inhibition (86.5%) at 0.1 M NaCl, defining its minimal inhibitory concentration (MIC) at 0.05 M. Full article

Iron, an essential element for virtually all known organisms, serves not only as a micronutrient but also as an energy source for bacteria. Iron-oxidizing microorganisms mediate Fe(II) oxidation under diverse redox conditions, yielding amorphous iron (hydr)oxides or crystalline iron minerals. This globally significant biogeochemical process drives modern iron cycling across terrestrial and aquatic ecosystems. The resulting biomineralization not only produces secondary minerals but also effectively immobilizes heavy metals, offering a sustainable strategy for environmental remediation. This review systematically examines (1) the biogeochemical mechanisms and mineralogical signatures of Fe(II) oxidation by four distinct iron oxidizers: acidophilic aerobes (e.g., Acidithiobacillus), neutrophilic microaerophiles (e.g., Gallionella), nitrate-reducing anaerobes (e.g., Acidovorax), and anoxygenic phototrophs (e.g., Rhodobacter); (2) research advances in heavy metal immobilization by biogenic iron minerals: adsorption, coprecipitation, and structural incorporation; and (3) the impact of pH, temperature, organic matter, and coexisting ions on Fe(II) oxidation efficiency and iron mineral formation by iron-oxidizing bacteria. By characterizing iron-oxidizing bacterial species and their functional processes under varying pH and redox conditions, this study provides critical insights into microbial behaviors driving the evolution of acid mine drainage (AMD). Full article

This study investigated the role of indigenous inoculum (primarily sulfur-oxidizing Acidithiobacillus thiooxidans and other acidophilic bacteria) in heavy metal removal from sewage sludge (SS) and anaerobic digested sludge (ADS). Four treatments were evaluated: inoculum + elemental sulfur (S/ADS + E), inoculum alone (S/ADS + B), elemental sulfur alone (S/ADS + S), and a control with no additives. After 7 days of bioleaching, SS and ADS exhibited comparable heavy metal removal rates on Ni (92–98%) and Pb (88–92%), which were significantly more mobilized than Cu (30–44%) and Cr (63–73%). After bioleaching treatment, residual metals in both sludge types were predominantly sequestered in the oxidizable (F3) and residual (F4) fractions, markedly reducing their environmental mobility and pollution risk during land application. The dewaterability performance, assessed via capillary suction time (CST), reached the optimal values in S + E and ADS + E within 24–48 h, after which CST increased alongside rising extracellular polymeric substances and dissolved organic carbon. While the S/ADS + B configuration exhibited marginally reduced Cu, Ni, and Pb removal efficiencies relative to S/ADS + E, it demonstrated superior dewaterability characteristics under equivalent reaction durations. These results suggest that limiting the sulfur (S₀) supply to moderate the growth and activity of autotrophic A. thiooxidans can maintain the bioleaching pH within 2.0–3.0, striking a balance between effective heavy metal removal and favorable dewatering performance. Full article

Mofettes or natural CO₂ springs release large amounts of geogenic CO₂ at ambient temperature, leading to long-term soil hypoxia in these extreme ecosystems. Thus, they can serve as natural long-term experiments in ecology and evolution and other environmental studies, providing stable long-term changes in abiotic factors that are most pronounced in mofette soils. This paper reviews basic research on rhizosphere processes, soil microbial communities, and microbial diversity in mofettes, focusing on reports describing the effects of altered soil gas regimes on root respiration and the diversity and community structure of archaea, bacteria, and fungi in soil. Furthermore, an insight into possible applications of mofette ecosystems is given. For more than 20 years, mofettes have provided new insights into the importance of long-term changes in abiotic environmental factors in regulating soil biodiversity, serving as a model for extreme ecosystems. Mofettes provide an innovative approach to the study of many ecological processes that occur slowly and, therefore, require extensive and lengthy observations and experiments, acting as a space-for-time substitution. Previous studies in mofettes around the world have determined plant responses to elevated CO₂ concentrations over multiple generations, described new species of collembolans and yeasts, and identified stable patterns in microbial communities describing specific acidophilic and methanogenic consortia of soil archaea and bacteria, as well as stable communities of plant symbiotic arbuscular mycorrhizal fungi. As the development of high-throughput molecular techniques has accelerated rapidly in the last decade, mofettes now serve more than ever as a natural long-term experimental system to study soil and rhizosphere ecology and contribute to further research on long-term ecological and evolutionary processes that are crucial for understanding past evolutionary events, managing future ecosystems, and predicting ecological responses to global change. Some recent developments target the specific geological and biological characteristics of these extreme ecosystems, including in terms of applications related to environmental impact assessment of carbon capture and storage systems, as well as conservation status, tourism, culture and education, i.e., broader ecosystem services of mofettes, which are addressed in this review together with basic research on soil biodiversity. Full article

Magnetosomes are magnetic nanocrystals synthesized by bacteria that have important application value in biomedicine. Therefore, it is very important to evaluate their biocompatibility. It has been reported that the extremophilic acidophilic bacterium Acidithiobacillus ferrooxidans, which is aerobic, can synthesize intracellular Fe₃O₄ magnetosomes. In this paper, we performed a comprehensive and systematic evaluation of the biocompatibility of magnetosomes with an average particle size of 53.66 nm from Acidithiobacillus ferrooxidans, including pharmacokinetics, degradation pathways, acute systemic toxicity, cytotoxicity, genotoxicity, blood index and immunotoxicity. The phase composition of the magnetosomes was identified as Fe3O4 through XRD and HRTEM analyses. Biocompatibility evaluation results showed that magnetosomes metabolized rapidly in rats and degraded thoroughly in major organs, with almost no residue. When the injection concentration was low (40 mg/kg, 60 mg/kg), magnetosomes would not cause pathological changes in the major organs of mice, basically. At the same time, magnetosomes had low cytotoxicity, genotoxicity, immunotoxicity and hemolysis rate, which proved that the magnetosomes synthesized by Acidithiobacillus ferrooxidans are magnetic nanomaterials with good biocompatibility. This research provides an important theoretical basis for the large-scale application of bacterial magnetosomes as functional magnetic nanomaterials. Full article

Cold-active enzymes hold promise for energy-efficient processes. Amylases are widely used in household and industrial applications, but only a few are cold-active. Here we describe three novel secreted amylases, Rho13, Ika2 and I3C6, all from bacteria growing in the cold and alkaline ikaite columns in Greenland. They all hydrolyzed starch to smaller malto-oligomers, but only Rho13 and Ika2 hydrolyzed cyclodextrins, and only Ika2 displayed transglycosylation activity. Ika2 forms a stable dimer, while both Rho13 and I3C6 are mainly monomeric. They all have optimal active temperatures around 30–35 °C and significant enzymatic activity below 20 °C, but Rho13 and I3C6 had an alkaline optimal pH, while Ika2 was markedly acidophilic. They showed complex dependence on Ca²⁺ concentration, with the activity of Rho13 and I3C6 following a bell-shaped curve and Ika2 being unaffected; however, removal of Ca²⁺ reduced the stability of all three enzymes. Loss of structure occurred well above the temperature of optimal activity, showing the characteristic psychrophilic divorce between activity and stability. MD simulations showed that Ika2 did not have a well-defined Ca²⁺ binding site, while Rho13 and I3C6 both maintained one stably bound Ca²⁺ ion. We identified psychrophilic features as higher levels of backbone fluctuations compared to mesophilic counterparts, based on a lower number of internal hydrogen bonds and salt bridges. This increased fluctuation was also found in regions outside the active site and may provide easier substrate access and accommodation, as well as faster barrier transitions. Our work sheds further light on the many ways in which psychrophilic enzymes adapt to increased catalysis at lower temperatures. Full article

In this research, the bio-oxidative capacity of three acidophilic bacterial strains (Acidithiobacillus thiooxidans, Leptospirillum ferriphilum, and an unidentified native consortium) are analyzed through the dissolution of cyanicidal species in a polymetallic sulfide mineral mainly composed of pyrite, quartz, sphalerite, and chalcocite. The main objective is the reduction in the amount of sodium cyanide used for the recovery of Au and Ag for the improvement of economic and environmental benefits in the processing of these minerals. Additionally, through a 2³ factorial experimental design, the effect of pH and pulp density (%) on bio-oxidation is evaluated. The results reveal that the bio-oxidation process of the mineral sulfide concentrate has been favored at low pH values and pulp density, favoring Cu species above all dissolution, which form stable complexes with cyanide, leading to excessive cyanide consumption. Therefore, at pH = 1.0 and pulp density of 10%, the catalytic activity of Acidithiobacillus thiooxidans achieves 73.30% Cu, 19.92% Pb, 57.37% Zn, and 25.17% Fe dissolution at the flask level and 83.18% Cu, 12.18% Pb, 55.36% Zn, and 40.98% Fe dissolution at the bioreactor level, allowing the dissolution of 89.5% and 80.4% of Au and Ag, respectively. Full article

Autotrophic sulfur-oxidizing bacteria can play a key role in the metal bioleaching from low-grade sulfide-containing ores. The most commonly used bioleaching group is presented with acidophilic bacteria of the order Acidithiobacillales. We studied the diversity of bacteria in the arsenopyrite gold-bearing ore and also discovered a wide distribution of neutrophilic non-thermophilic bacteria Thermithiobacillus plumbiphilus in this ore, as well as its drainage and flotation concentrate. For the first time, T. plumbiphilus was isolated from the natural arsenic-containing mineral material. The first description of complete genome for the species T. plumbiphilus was also carried out and discovered genes providing the As resistance. Culturing the isolated strain T. plumbiphilus AAFK confirmed the found bacterial resistance to arsenite and cocadylate during the effective thiosulfate oxidation. Experiments on the arsenopyrite bioleaching showed that T. plumbiphilus AAFK can be used as an auxiliary bacterial culture capable of oxidizing reduced / intermediate sulfur compounds. The genetic basis of the T. plumbiphilus AAFK resistance to the arsenic compounds is discussed; the mechanisms are similar with the ones known for acidophilic thiobacilli. The biofilm formation is shown for the first time for T. plumbiphilus; presumably, it could provide some protection and immobilization of the cells. Structures of the T. plumbiphilus AAFK cells and their production of outer membrane vesicles are described and discussed. Full article

Extremophiles, microorganisms blooming in extreme environmental conditions, hold particular significance in the domain of microbial research. This review paper focuses on extremophilic microorganisms, emphasizing their adaptations and the diverse products they generate, with a particular emphasis on exopolysaccharides (EPSs). EPSs, high molecular weight carbohydrate biopolymers, stand out as valuable products with applications across various industries. The review explores EPS production by bacteria in extreme conditions, including thermophilic, halophilic, and psychrophilic environments. Noteworthy examples, such as B. thermantarcticus and H. smyrnensis AAD6T, highlight the vast potential of extremophiles in EPS production. Additionally, the paper explores the major synthesis pathways of EPSs, shedding light on the factors influencing biosynthesis. The commercial significance of EPSs, especially for extremophiles, is underlined by their applications in medicine, food, environmental protection, agriculture, cosmetics, and more. Furthermore, the review sheds light on the role of extremophiles in various ecosystems, such as acidophiles, alkaliphiles, halophiles, hyperthermophiles, oligotrophs, osmophiles, piezophiles, and radioresistant organisms. This comprehensive analysis highlights the broad impact of extremophilic microorganisms and their EPS products in scientific exploration and commercial innovation. Full article

Bioleaching, a process catalyzed by acidophilic microorganisms, offers a sustainable approach to metal extraction from sulfide minerals. Chalcopyrite, the world’s most abundant copper sulfide, presents challenges due to surface passivation limiting its bioleaching efficiency. Also, indigenous species and microbial communities may present high copper extraction rates and offer new possibilities for application in bioleaching processes. This study examines the bioleaching potential of microbial isolates and communities obtained from Amolanas Mine in Chile. Samples were collected, cultivated, and identified by Sanger sequencing. The bioleaching potential and biofilm formation of isolates and enrichments were evaluated on pyrite and chalcopyrite. The results show the isolation of nine Leptospirillum and two Acidithiobacillus strains. The bioleaching experiments demonstrated good copper bioleaching potentials of the Leptospirillum I2CS27 strain and EICA consortium (composed mainly of Leptospirillum ferriphilum, Acidiphilium sp., and Sulfobacillus thermosulfidooxidans), with 11% and 25% copper recovery rates, respectively. Microbial attachment to the surface mineral was not mandatory for increasing the bioleaching rates. Our findings underscore the importance of indigenous microbial communities in enhancing copper bioleaching efficiency. Full article

Extreme acidophilic bacteria like Leptospirillum sp. require an efficient enzyme system to counteract strong oxygen stress conditions in their natural habitat. The genome of Leptospirillum sp. CF-1 encodes the thioredoxin-fold protein TFP2, which exhibits a high structural similarity to the thioredoxin domain of E. coli CnoX. CnoX from Escherichia coli is a chaperedoxin that protects protein substrates from oxidative stress conditions using its holdase function and a subsequent transfer to foldase chaperones for refolding. Recombinantly produced and purified Leptospirillum sp. TFP2 possesses both thioredoxin and chaperone holdase activities in vitro. It can be reduced by thioredoxin reductase (TrxR). The tfp2 gene co-locates with genes for the chaperone foldase GroES/EL on the chromosome. The “tfp2 cluster” (ctpA-groES-groEL-hyp-tfp2-recN) was found between 1.9 and 8.8-fold transcriptionally up-regulated in response to 1 mM hydrogen peroxide (H₂O₂). Leptospirillum sp. tfp2 heterologously expressed in E. coli wild type and cnoX mutant strains lead to an increased tolerance of these E. coli strains to H₂O₂ and significantly reduced intracellular protein aggregates. Finally, a proteomic analysis of protein aggregates produced in E. coli upon exposition to oxidative stress with 4 mM H₂O₂, showed that Leptospirillum sp. tfp2 expression caused a significant decrease in the aggregation of 124 proteins belonging to fifteen different metabolic categories. These included several known substrates of DnaK and GroEL/ES. These findings demonstrate that Leptospirillum sp. TFP2 is a chaperedoxin-like protein, acting as a key player in the control of cellular proteostasis under highly oxidative conditions that prevail in extreme acidic environments. Full article

This study presents findings regarding the kinetics of ferrous iron oxidation in solution mediated by Acidithiobacillus ferrooxidans bacteria within a continuous-flow bioreactor employing diverse types of immobilizers. The objective is to augment the rate of ferrous iron oxidation in solutions utilizing an immobilizer for Acidithiobacillus ferrooxidans strains. Immobilization represents a promising avenue for enhancing the efficiency of Fe²⁺ oxidation via acidophilic ferrooxidizing bacteria, leading to a several-fold increase in oxidation rate. A comparative analysis was conducted to evaluate the efficacy of different types of immobilizer in facilitating iron oxidation within a continuous-flow bioreactor, including the application of wood chips coated with Fe(OH)₃. The results indicate that wood chips coated with iron hydroxide serve as effective type of immobilizer, facilitating the robust attachment of Acidithiobacillus ferrooxidans via electrostatic interactions between negatively charged bacteria and positively charged surfaces. Experimental investigations were conducted using novel immobilization matrices in pilot-scale tests simulating the underground borehole leaching (UBL) of uranium. The bioactivation of leaching solutions enhances the efficiency and environmental compatibility of UBL compared to conventional chemical oxidation methods. The relationships between redox potential and ferric iron content in bioactivated solutions during the UBL of uranium were delineated. The significance of this study lies in its elucidating the pivotal role of Fe²⁺ oxidation in uranium extraction processes, particularly in the context of UBL. By employing bioactivation mediated by Acidithiobacillus ferrooxidans, the study demonstrates not only enhanced uranium extraction efficiency, but also markedly improved environmental sustainability compared to traditional chemical oxidation methods. The findings reveal crucial correlations between redox potential and ferric iron concentration in bioactivated solutions. Full article

Conserved Histidine Alpha-helical Domain (CHAD) proteins attached to the surface of polyphosphate (PolyP) have been studied in some bacteria and one archaeon. However, the activity of CHAD proteins is unknown beyond their interaction with PolyP granules. By using bioinformatic analysis, we report that several species of the biomining acidophilic bacteria contain orthologs of CHAD proteins with high sequence identity. Furthermore, the gene coding for the CHAD protein is in the same genetic context of the enzyme polyphosphate kinase (PPK), which is in charge of PolyP synthesis. Particularly, the group of ppk and CHAD genes is highly conserved. Metallosphaera sedula and other acidophilic archaea used in biomining also contain CHAD proteins. These archaea show high levels of identity in genes coding for a cluster having the same organization. Amongst these genes are chad and ppx. In general, both biomining bacteria and archaea contain high PolyP levels and are highly resistant to heavy metals. Therefore, the presence of this conserved genetic organization suggests a high relevance for their metabolism. It has been formerly reported that a crystallized CHAD protein contains a copper-binding site. Based on this previous knowledge, in the present report, it was determined that all analyzed CHAD proteins are very conserved at their structural level. In addition, it was found that the lack of YgiF, an Escherichia coli CHAD-containing protein, decreases copper resistance in this bacterium. This phenotype was not only complemented by transforming E. coli with YgiF but also by expressing CHAD from Acidithiobacillus ferrooxidans in it. Interestingly, the strains in which the possible copper-binding sites were mutated were also more metal sensitive. Based on these results, we propose that CHAD proteins are involved in copper resistance in microorganisms. These findings are very interesting and may eventually improve biomining operations in the future. Full article