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Acidithiobacillus ferrooxidans is an acidophilic and chemolithotrophic sulfur- and iron-oxidizing bacterium that has been widely used in the bioleaching process for extracting metals. Extracellular polymeric substances (EPS) are essential for bacteria-ore interactions, and the regulation of EPS synthesis could be an important way of influencing the...
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... on the enhancement of the cell growth, sulfur-metabolism activity, EPS synthesis, biofilm formation, and bioleaching efficiency by qs-Ⅰ, a model was outlined to illustrate the role of AfeI/R in the A. ferrooxidans-driven leaching process of minerals (Figure 7). The elevation of the qs-I expression level could promote the synthesis and secretion of EPS and cell growth, which stimulates the formation of biofilm on the surface of ores. ...
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In this study, the bioleaching of low-grade nickel-copper concentrate was carried out using the nutrient medium containing yeast extract (YE) at temperature range of from 40 to 60°C in order to study the dependence of biooxidation rate and Cu and Ni extraction levels on the temperature and the presence of organic compounds. Mixed culture of the str...
The aim of the present work was to perform copper, nickel, and platinum group metals (PGMs) recovery from low-grade copper–nickel concentrate containing pyrrhotite, pentlandite, and chalcopyrite by bioleaching in stirred tank reactors in batch mode and subsequent cyanidation. The concentrate contained (%) Fe 32.7, Cu 0.7, Ni 2.3, Stotal 20.9, Ssulf...
The biological leaching of metals from different waste streams by bacteria is intensively investigated to address metal recycling and circular economy goals. However, usually external addition of sulfuric acid is required to maintain the low pH optimum of the bacteria to ensure efficient leaching. Extremely acidophilic Acidithiobacillus spp. produc...
Cell adhesion is generally a prerequisite to the microbial bioleaching of sulfide minerals, and surface biofilm formation is modulated via quorum sensing (QS) communication. We explored the impact of the overexpression of endogenous QS machinery on the covellite bioleaching capabilities of Acidithiobacillus ferrooxidans, a representative acidophili...
Communication is important for organisms living in nature. Quorum sensing system (QS) are intercellular communication systems that promote the sociality of microbes. Microorganisms could promote cell-to-cell cooperation and population density to adapt to the changing environment through QS-mediated regulation that is dependent on the secretion and...
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... AHL-QS-overexpressing strains show significant differences in biofilm formation. The cultivation of A. ferrooxidans in pyrite and the overexpression of AHL-QS led to a significant increase in EPS synthesis [106]. Overexpression of the AHL-QS or the afeI-only gene strains shows enhanced adhesion to cobaltite [107]. ...
Bioleaching has gained significant attention as a cost-effective and environmentally friendly approach for extracting metals from low-grade ores and industrial byproducts. The application of acidophiles in bioleaching has been extensively studied. Among the various mechanisms leaching microorganisms utilize, quorum sensing (QS) is pivotal in regulating their life activities in response to population density. QS has been confirmed to regulate bioleaching, including cell morphology, community structure, biofilm formation, and cell metabolism. Potential applications of QS have also been proposed, such as increasing mineral leaching rates by adding signaling molecules. This review is helpful for comprehensively understanding the role of QS in bioleaching and promoting the practical application of QS-based strategies in bioleaching process optimization.
... For example, it is shown that Acidithiobacillus ferrooxidans can be used to remove heavy metals in acidic wastewater (Min et al. 2017). Also, it is indicated that Acidithiobacillus ferrooxidans is one of the efficient bioleaching bacteria modulating the bioleaching process (Gao et al. 2020). ...
Bioleaching is a common and eco-friendly method for the metals mobilization from mines, contaminated soils and wastes and it can be used in metal extraction and bioremediation. Due to the fact that these processes are considered as metabolism-dependent processes, isolation and identifying of the strains with high resistance features in responsible bacteria are one of the most important steps to have. In present study, an Iranian new isolate of iron-oxidizing bacteria was characterized. The phylogenetic analysis and 16S rRNA gene sequence of strain ZT-94 indicated that this strain is related to Acidithiobacillus ferrooxidans. It is investigated that the ferrous iron oxidation was increased dramatically in the early hours of bacterial growth and the ferrous iron (Fe2+) was completely oxidized at 30 h. According to the results, strain ZT-94 had the high tolerance capability to U, Ba, Al and Se. Iron oxidation by strain ZT-94 was inhibited by the addition of 312.5 mg/L Se and 70 mg/L Te but concentrations above 5000 mg/L of Ba and 2000 mg/L Al had no inhibitory effect on bacterial growth. In addition, strain ZT-94 was able to grow in the pH range of 1–4, temperatures at 25–35 °C. Results showed no inhibitory effects on bacterial growth rate in presence of 0.1 w/v organic compounds like fructose and glucose but a delayed growth was detected in presence of yeast extract in comparison with the others. The results showed that strain ZT-94 had high environmental adaptability and can be introduced as a suitable and valuable candidate for research in the bioleaching and bioremediation processes.
... Exposure to a synthetic QS blocker also revealed that AfeI/R mediates Cu 2+ resistance in A. ferrooxidans (Wenbin et al., 2011). In addition, the overexpression of afeI/R operon suggested the important roles of Afe/R in the growth of A. ferrooxidans in S 0 -enriched media and in improving the bioleaching efficiency of A. ferrooxidans to ores (Gao et al., 2020). However, although some functions of AfeI/R have been identified via the addition assays of exogenous signal molecules, the understanding of the roles of AfeI/R in A. ferrooxidans has not been fully achieved. ...
A LuxI/R‐like quorum sensing (QS) system (AfeI/R) has been reported in the acidophilic and chemoautotrophic Acidithiobacillus spp. However, the function of AfeI/R remains unclear because of the difficulties in genetic manipulation of these bacteria. Here, we constructed different afeI mutants of the sulfur‐ and iron‐oxidizer A. ferrooxidans, identified the N‐acyl homoserine lactones (acyl‐HSLs) synthesized by AfeI, and determined the regulatory effects of AfeI/R on genes expression, extracellular polymeric substance (EPS) synthesis, energy metabolism, cell growth and population density of A. ferrooxidans in different energy substrates. Acyl‐HSLs ‐mediated distinct regulation strategies were employed to influence bacterial metabolism and cell growth of A. ferrooxidans cultivated in either sulfur or ferrous iron. Based on these findings, an energy‐substrate‐dependent regulation mode of AfeI/R in A. ferrooxidans was illuminated, that AfeI/R could produce different types of acyl‐HSLs and employ specific acyl‐HSLs to regulate specific genes in response to different energy substrates. The discovery of the AfeI/R‐mediated substrate‐dependent regulatory mode expands our knowledge on the function of QS system in the chemoautotrophic sulfur‐ and ferrous iron‐oxidizing bacteria, and provides new insights in understanding energy metabolism modulation, population control, bacteria‐driven bioleaching process, and the coevolution between the acidophiles and their acidic habitats. This article is protected by copyright. All rights reserved.
... In this same sense, it has been shown that a high concentration of cells can overcome adverse conditions, probably because it encourages the cellular communication (Atkinson and Williams, 2009;Gao et al., 2020). At. ferrooxidans presents quorum sensing of type I (Zhang et al., 2018), and this communication allows cell-cell signaling through self-inducing molecules, allowing the regulation of different cell processes that are dependent on the density of the microbial population, including EPS production, adaptation and tolerance (Gao et al., 2020). ...
... In this same sense, it has been shown that a high concentration of cells can overcome adverse conditions, probably because it encourages the cellular communication (Atkinson and Williams, 2009;Gao et al., 2020). At. ferrooxidans presents quorum sensing of type I (Zhang et al., 2018), and this communication allows cell-cell signaling through self-inducing molecules, allowing the regulation of different cell processes that are dependent on the density of the microbial population, including EPS production, adaptation and tolerance (Gao et al., 2020). ...
Acidithiobacillus ferrooxidans, together with other microorganisms, has an important role on biohydrometallurgical processes. Such bacterium gets its energy from the oxidation of ferrous ion and reduced sulfur; in the first case, the accumulation of ferric ion as a product can cause its inhibition. It is known that the extracellular polymeric substances (EPS) may have an important role in the adaptation and tolerance to diverse inhibiting conditions. In the present study, it was tested how D-galactose can influence the production of extracellular polymeric substances (EPS) on At. ferrooxidans by evaluating at the same time its biooxidant activity and capacity to tolerate high concentrations of ferric ion. The visualization and quantification of EPS was done through a confocal laser scanning microscope (CLSM). The results show that at low cellular concentrations, the D-galactose inhibits the microbial growth and the biooxidation of ferrous ion; however, when the quantity of microorganisms is high enough, the inhibition is not present. By means of chemostat tests, several concentrations of D-galactose (0; 0.15; 0.25; and 0.35%) were evaluated, thus reaching the highest production of EPS when using 0.35% of this sugar. In cultures with such concentration of D-galactose, the tolerance of the bacterium was tested at high concentrations of ferric ion and it was compared with cultures in which sugar was not added. The results show that cultures with D-galactose reached a higher tolerance to ferric ion (48.15 ± 1.9 g L −1) compare to cultures without adding D-galactose (38.7 ± 0.47 g L −1 ferric ion). Also it was observed a higher amount of EPS on cells growing in the presence of D-galactose suggesting its influence on the greater tolerance of At. ferrooxidans to ferric ion. Therefore, according to the results, the bases of a strategy are considered to overproduce EPS by means of At. ferrooxidans in planktonic state, so that, it can be used as a pre-treatment to increase its resistance and tolerance to high concentrations of ferric ion and improve the efficiency of At. ferrooxidans when acting in biohydrometallurgical processes.
Electronic waste, also known as e-waste, is the discarded or by-products of electronic appliances, constituting a major percentage of the total solid waste produced globally. Such e-waste is mostly composed of plastics, various heavy metals, azo dyes, and xenobiotic components, which are mostly non-biodegradable or less degradable in nature. As a result, they increase environmental toxicity, preventing the growth of crops and causing health issues for humans and other animals. On the other hand, recycling e-waste may also lead to the consumption of heavy metals through water or the inhalation of polluted air after combustion, which may cause various health issues such as asthma, nerve, respiratory, kidney, liver disease, and even cancer. Hence, microbial degradation of e-waste has become a new trend in managing such solid wastes. However, their mode of action is somewhat less explored. Microbes degrade various components of e-waste through a number of mechanisms such as bioleaching, biosorp-tion, biotransformation, bioaccumulation, and biomineralization. Some microorganisms release enzymes such as reductases, laccases, esterases, carboxylesterases, catalases, and dioxygenases for the bioconversion of various components of e-waste into their less toxic forms. This review provides insight into the role of microbes in the conversion of various components of e-wastes such as polyaromatic hydrocarbons (PAHs), azo dyes, and heavy metals and their mode of action.
Biomass waste management relies on enzymes to catalyze chemical reactions that turn waste into usable goods. Enzymes can convert biomass waste polysaccharides, proteins, and lipids into glucose, fatty acids, and amino acids. Simpler chemicals can be energy sources or building blocks. They can transform biomass waste cellulose into glucose and, eventually, ethanol. Enzymes can transform proteins and lipids into bio-solids for various uses. Enzymes can also break down lignin, a complex polymer in plant biomass, producing aromatic chemicals for numerous benefits. Enzymes are used in biodegradation, biofuel production, bioremediation, pulping, and animal feed. Microbial enzymatic processes break down organic materials in biodegradation. This procedure decomposes food waste and yard clippings into compost or fertilizer. Enzymes accelerate organic waste breakdown. Biomass is converted into biofuel. Enzymes convert biomass into sugars for biofuels. This trash management method could cut fossil fuel use. Microorganisms degrade contaminants in bioremediation. They also speed up this process, making pollution removal more efficient, and turn woody resources into pulp for papermaking in pulping. This approach reduces wood waste in landfills and paper production energy and materials. Finally, enzymes can make animal feed. They can improve animal feed digestibility and nutrient utilization. Animal health and growth may improve. In this work, we examine the possibility of developing additional enzymatic processes to support sustainable waste management practices and review the existing state of knowledge on the application of enzymes in biomass waste management.
Methanethiol (MeSH) and dimethyl sulfide (DMS) are important volatile organic sulfur compounds involved in atmospheric chemistry and climate regulation. However, little is known about the metabolism of these compounds in the ubiquitous marine vibrios. Here, we investigated MeSH/DMS production and whether these processes were regulated by quorum-sensing (QS) systems in Vibrio harveyi BB120. V. harveyi BB120 exhibited strong MeSH production from methionine (Met) (465 nmol mg total protein−1) and weak DMS production from dimethylsulfoniopropionate (DMSP) cleavage. The homologs of MegL responsible for MeSH production from L-Met widely existed in vibrio genomes. Using BB120 and its nine QS mutants, we found that the MeSH production was regulated by HAI-1, AI-2 and CAI-1 QS pathways, as well as the luxO gene located in the center of this QS cascade. The regulation role of HAI-1 and AI-2 QS systems in MeSH production was further confirmed by applying quorum-quenching enzyme MomL and exogenous autoinducer AI-2. By contrast, the DMS production from DMSP cleavage showed no significant difference between BB120 and its QS mutants. Such QS-regulated MeSH production may help to remove excess Met that can be harmful for vibrio growth. These results emphasize the importance of QS systems and the MeSH production process in vibrios.
Biomining processes utilize microorganisms, such as Acidithiobacillus, to extract valuable metals by producing sulfuric acid and ferric ions that dissolve sulfidic minerals. However, excessive production of these compounds can result in metal structure corrosion and groundwater contamination. Synthetic biology offers a promising solution to improve Acidithiobacillus strains for sustainable, eco-friendly, and cost-effective biomining, but genetic engineering of these slow-growing microorganisms is challenging with current inefficient and time-consuming methods. To address this, we established a CRISPR-dCas9 system for gene knockdown in A. ferridurans JAGS, successfully downregulating the transcriptional levels of two genes involved in sulfur oxidation. More importantly, we constructed an all-in-one CRISPR-Cas9 system for fast and efficient genome editing in A. ferridurans JAGS, achieving seamless gene deletion (HdrB3), promoter substitution (Prus to Ptac), and exogenous gene insertion (GFP). Additionally, we created a HdrB-Rus double-edited strain and performed biomining experiments to extract Ni from pyrrhotite tailings. The engineered strain demonstrated a similar Ni recovery rate to wild-type A. ferridurans JAGS but with significantly lower production of iron ions and sulfuric acid in leachate. These high-efficient CRISPR systems provide a powerful tool for studying gene functions and creating useful recombinants for synthetic biology-assisted biomining applications in the future.
In modern societies, the accumulation of vast amounts of waste Li-ion batteries (WLIBs) is a grave concern. Bioleaching has great potential for the economic recovery of valuable metals from various electronic wastes. It has been successfully applied in mining on commercial scales. Bioleaching of WLIBs can not only recover valuable metals but also prevent environmental pollution. Many acidophilic microorganisms (APM) have been used in bioleaching of natural ores and urban mines. However, the activities of the growth and metabolism of APM are seriously inhibited by the high concentrations of heavy metal ions released by the bio-solubilization process, which slows down bioleaching over time. Only when the response mechanism of APM to harsh conditions is well understood, effective strategies to address this critical operational hurdle can be obtained. In this review, a multi-scale approach is used to summarize studies on the characteristics of bioleaching processes under metal ion stress. The response mechanisms of bacteria, including the mRNA expression levels of intracellular genes related to heavy metal ion resistance, are also reviewed. Alleviation of metal ion stress via addition of chemicals, such as spermine and glutathione is discussed. Monitoring using electrochemical characteristics of APM biofilms under metal ion stress is explored. In conclusion, effective engineering strategies can be proposed based on a deep understanding of the response mechanisms of APM to metal ion stress, which have been used to improve bioleaching efficiency effectively in lab tests. It is very important to engineer new bioleaching strains with high resistance to metal ions using gene editing and synthetic biotechnology in the near future.
