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In the present work, bioleaching of two valuable metals of cobalt (Co) and nickel (Ni) from spent lithium-ion batteries (LIBs) of laptop by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans through a novel adaptation procedure was investigated. Different bioleaching methods including A. ferrooxidans and A. thiooxidans spent medium, A. ferrooxidans one-step and two-step bioleaching were carried out. The effect of silver ion on the bioleaching of Co and Ni in these methods was evaluated. Moreover, a novel strain adaptation approach to the toxic solid content of the battery powder was chosen, which resulted in a very short adaptation time and bioleaching (2 days). Even though silver ion did not have a significant effect on the spent medium method, it had an increasing effect of 26% and 7%, for Co and Ni recovery, respectively, on two-step bioleaching with silver ion-adapted A. ferrooxidans, in gradual addition of the battery powder. The highest extraction results in the spent medium method were 45.2% and 71.5% for Co and Ni, respectively, and a very high extraction yield of 99.95% for these metals was achieved in a short time of only 3 days by two-step bioleaching with gradual addition of the solid content and in the presence of Ag

There are several natural and anthropomorphic environments where iron- and/or sulfur-oxidizing bacteria thrive in extremely acidic conditions. These acidophilic chemolithautotrophs play important roles in biogeochemical iron and sulfur cycles, are critical catalysts for industrial metal bioleaching operations, and have underexplored potential in future biotechnological applications. However, their unique growth conditions complicate the development of genetic techniques. Over the past few decades genetic tools have been successfully developed for Acidithiobacillus ferrooxidans, which serves as a model organism that exhibits both iron- and sulfur-oxidizing capabilities. Conjugal transfer of plasmids has enabled gene overexpression, gene knockouts, and some preliminary metabolic engineering. We highlight the development of genetic systems and recent genetic engineering of A. ferrooxidans, and discuss future perspectives.

Trehalose is a type of carbohydrate that protects against different types of stress and is also used as a source of carbon storage in prokaryotes. There are four different ways of synthesizing trehalose in Acidithiobacillus ferrivorans and two in Acidithiobacillus ferrooxidans, but its purpose remains unknown. This study aimed to measure the production of trehalose under different conditions by quantifying it in three culture media at two different temperatures. The growth kinetics of both species were also assessed, and the trehalose concentration was analysed during the early stationary phase using an enzymatic method. The results showed that the modified 9K medium with ferrous iron at 28°C had the highest production of trehalose, with A. ferrivorans CF27 having a higher production of 0.34 µmol/mg protein compared to A. ferrooxidans ATCC 23270 at 0.31 µmol/mg protein. When using CuS, the production of trehalose was lower, with 0.02 and 0.03 µmol/mg protein for A. ferrivorans CF27 and A. ferrooxidans ATCC 23270, respectively, while no trehalose was detected in the presence of zinc. At 15°C, the enzymatic method did not detect any trehalose in all three culture media, this would indicate that this carbohydrate does not protect against low temperatures in either species., La trehalosa es un tipo de carbohidrato, que en procariotas protege contra diferentes tipos de estrés y también se utiliza como fuente de almacenamiento de carbono. Hay cuatro formas diferentes de sintetizar trehalosa en Acidithiobacillus ferrivorans y dos en Acidithiobacillus ferrooxidans, pero su propósito sigue siendo desconocido. Este estudio tuvo como objetivo medir la producción de trehalosa en diferentes condiciones mediante su cuantificación en tres medios de cultivo a dos temperaturas diferentes. También se evaluó la cinética de crecimiento de ambas especies y se analizó la concentración de trehalosa durante la fase estacionaria temprana mediante un método enzimático. Los resultados mostraron que el medio 9K modificado con hierro ferroso a 28 °C tuvo la mayor producción de trehalosa, con A. ferrivorans CF27 con una mayor producción de 0.34 µmol/mg de proteína en comparación con A. ferrooxidans ATCC 23270 a 0.31 µmol/mg de proteína. Al utilizar CuS, la producción de trehalosa fue menor, con 0.02 y 0.03 µmol/mg de proteína para A. ferrivorans CF27 y A. ferrooxidans ATCC 23270, respectivamente, mientras que en presencia de zinc no se detectó trehalosa. A 15°C, el método enzimático no detectó trehalosa en los tres medios de cultivo, lo que indicaria que este carbohidrato no protege contra las bajas temperaturas en ninguna de las especies.

Among the many extraction technologies for recovering metal resources from tailings, bioleaching technology is gradually showing its momentum. In our research, the enhanced effect of biochar on the bioleaching of stone coal tailings by Thiobacillus ferrooxidans (T. ferrooxidans) has been explored. In the static bioleaching experiment for 10 days, the leaching rate of vanadium (V) and copper (Cu) increased by 26.8% and 21.0% respectively after adding 5 g/L biochar. The dynamic bioleaching experiment further verified that under the promotion of biochar, the 44 day cumulative leaching rate of V and Cu increased by 15.3% and 14.5%, respectively. The promoting effect of biochar on T. ferrooxidans was mainly reflected in two aspects. The unique porous structure of biochar created a microenvironment for free microorganisms for inhabitation, while storing abundant nutrients. Biochar can also act as an excellent electronic medium to promote electron transfer, improving the oxidation ability of T. ferrooxidans on Fe2+. Furthermore, the presence of biochar may effectively inhibit the formation of jarosite precipitation on tailings in bioleaching, thereby improving the dissolution of tailings and the release of metal elements. This study demonstrates that biochar-enhanced bioleaching may be an efficient and environmentally friendly method for recovering metal resources from tailings.

The success of Next generation sequencing (NGS) technology over the past decades has led to a better understanding of complex microbial communities in such environment. Here, we employed NGS to monitor sulfur oxidizing bacteria (SOB) community from cassava starch industry (BPT), which can oxidize H2S into sulfate or elemental sulfur under aerobic conditions. Microbial sludge was collected from two sampling points comprising starting sludge (BPT1) and recirculating sludge (BPT2) of the biotrickling filter. gDNA was extracted from BPT1 and BPT2 samples and removed other contaminations by using the GenepHarM Gel/PCR Kit (Geneaid). DNA concentrations and DNA purity were analyzed by using gel electrophoresis and NanoDrop™ 1000 Spectrophotometer, respectively. Analysis of SOB species using NGS technique was based on the hypervariable regions V4 on the 16S rRNA gene. The comparative genomic hybridization (CGH) microarray probes for detection and identification of SOB species-strain that high expression of soxAXBYZ and fccAB genes in the cassava starch industry. For the recirculating sludge (BPT2), the bacterial communities were dominated by Sulfurimonas (13.7%) followed by Synechococcus (9.4%), Hydrogenophaga (6.5%), Methanosaeta (2.4%), and Acidithiobacillus (2.1%), the same dominant genera were also found in the starting sludge (BPT1), but with slightly different abundancy. The heatmap revealed that Acidithiobacillus caldus species (33.9%–49.9%) could play a vital role in eliminating H2S in biogas from the cassava starch industry. The CGH microarray indicated that Thiothrix, Paracoccus, Sulfurimonas, Hydrogenophaga, Magnetospirillum, Rhodoplanes, Syntrophomonas, Pseudomonas, Sulfuricurvum, and Arcobacter were dominant genus, that has a high expression of sulfur oxidation genes in biotrickling filter.

Bioleaching is of increasing interest because of its high efficiency in improving sludge dewaterability and removing heavy metals from sewage sludge. However, in traditional single-phase bioleaching, a high-efficiency level cannot be maintained continuously, wherein the microbial synergistic effect is disrupted at a low pH environment. Therefore, in this study, a series of multi-compartment-baffled flow trials were performed to assess the effects of phase separation on sludge bioleaching by comparing a two-phase trial with two single-phase trials. Energy substrate and part of the bioleached sludge were introduced separately into two compartments to form two phases, namely selection phase and bioleaching phase. The results show that phase separation apparently shortened the start-up duration of sludge bioleaching from 7 days in a single-phase bioleaching to 4 days in two-phase bioleaching. The dewaterability of bioleached sludge was also enhanced by phase separation with relative decreases of 25.0-33.3% for specific resistance to filtration and 14.2% for capillary suction time, which was attributed to lower pH values, zeta potential closer to zero, and less dissolved organic matter in bioleached sludge after two-phase bioleaching. Phase separation generally increased the removal ratios of heavy metals during sludge bioleaching by -0.79 to 2.60%, 11.06 to 15.04%, 4.45 to 11.03%, 17.98 to 23.46%, 7.20 to 9.28%, -9.22 to -2.46%, and -6.72 to -10.68% for As, Cd, Cr, Cu, Ni, Pb, and Zn, respectively. Phase separation also enriched the Acidithiobacillus spp. and reduced the inactivation of acid-tolerant fungi, which can be conducive to better synergistic effect, and therefore maintain long-term stable state in the bioleaching phase of the two-phase bioleaching process.

Sulfide-containing mine waste was oxidized to produce acid mine drainage, which lead to acidification of surrounding soil and downstream rivers and posed a threat to the surrounding environment. Quartz often coexists with sulfide minerals and affects the oxidation of sulfide minerals. In order to explore the role of quartz in the bio-oxidation of sulfide minerals in mine solid waste, the mixed minerals of quartz and sulfide minerals were bio-oxidized by Acidithiobacillus ferrooxidans. The results showed that quartz could improve the microbial activity and increase the acid production of sulfide minerals. The larger the proportion of quartz in bio-oxidation of sulfide minerals, the less the production of secondary minerals such as jarosite, and the larger the leaching amount of iron and sulfate. This research provides new ideas for speeding up the bio-oxidation of sulfide mineral to remove iron and sulfate. It provides a new way to solve acid pollution caused by oxidation of sulfide minerals.

The effect of bio-oxidation and neutral atmospheric oxidation pre-treatment of refractory gold concentrates on gold and silver extraction during cyanidation was investigated. A series of pre-treatment experiments was conducted on three high sulfur (> 9%) refractory concentrates with 0.92–1.25 g/t gold and 64–90 g/t silver. Cyanidation of the pre-treated concentrates using both methods was compared with respect to gold and silver leaching efficiency and reagent consumption. Bio-oxidation experiments were carried out using a mixed culture of Acidithiobacillus ferroxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans. The experimental results showed that both neutral atmospheric oxidation and bio-oxidation processes led to improvements in gold and silver extractions. The best result was achieved using neutral atmospheric oxidation at 20% pulp density, increasing gold and silver extraction to 78 and 73%, respectively. This corresponds to increases of 47 and 37% over direct cyanidation of the untreated concentrate. For bio-oxidation pre-treatment, increasing the duration had a negative effect on silver leaching efficiency due to jarosite formation. Cyanide consumption was reduced after neutral atmospheric oxidation and increased after bio-oxidation pre-treatment. Lime consumption increased while thiocyanate production was decreased after both pre-treatment methods. In terms of economic efficiency, neutral atmospheric oxidation pre-treatment was superior to bio-oxidation pre-treatment. Potential value in $USD per ton of three refractory concentrates with and without pre-treatment with neutral atmospheric oxidation and bio-oxidation.

The present work deals with the use of iron/sulfur-oxidizing bacterium Acidithiobacillus ferrooxidans for the desulfurization of a coal sample from Assam, India. The coal sample contains 3.87% w/w ...

Banana crops require large amounts of fertilizers to maintain nutrients levels and achieve satisfactory yields. The use of biological fertilizers combined with organic waste is an efficient and sus...

Acidithiobacillus ferrooxidans is an acidophilic chemolithoautotroph that is commonly reported to exhibit diauxic population growth behavior where ferrous iron is oxidized before elemental sulfur when both are available, despite the higher energy content of sulfur. We have discovered sulfur dispersion formulations that enables sulfur oxidation before ferrous iron oxidation. The oxidation of dispersed sulfur can lower the culture pH within days below the range where aerobic ferrous iron oxidation can occur. Thus, ferric iron reduction can be observed quickly which had previously been reported over extended incubation periods with untreated sulfur. Therefore, we demonstrate that this substrate utilization pattern is strongly dependent on the cell loading in relation to sulfur concentration, sulfur surface hydrophobicity, and the pH of the culture. Our dispersed sulfur formulation, lig-sulfur, can be used to support the rapid antibiotic selection of plasmid-transformed cells, which is not possible in liquid cultures where ferrous iron is the main source of energy for these acidophiles. Furthermore, we find that media containing lig-sulfur supports higher production of green fluorescent protein compared to media containing ferrous iron. The use of dispersed sulfur is a valuable new tool for the development of engineered A. ferrooxidans strains and it provides a new method to control iron and sulfur oxidation behaviors.

Aims Acidithiobacillus caldus is an important sulphur-oxidizing bacterium that plays crucial roles in the bioleaching industry. This study aims to analyse the optimal reference gene for real-time quantitative PCR (RT-qPCR) under different conditions and investigate the transcription levels of the sigma factor genes in the stress response. Methods and results We selected six housekeeping genes and analysed them via RT-qPCR using two energy resources, under four stress conditions. Three statistical approaches BestKeeper, geNorm, and NormFinder were utilized to determine transcription stability of these reference genes. The gapdH gene was the best internal control gene using elemental sulphur as an energy resource and under heat stress, map was the best internal control gene under pH and osmotic stress, era was the best internal control gene for the K2 S4 O6 energy resource, and rpoC was the best internal control gene under Cu2+ stress. Furthermore, the expressional levels of 11 sigma factors were analysed by RT-qPCR in the stress response. Conclusions Stable internal control genes for RT-qPCR analysis of A. caldus were determined, and the expression patterns of sigma factor genes of A. caldus were investigated. Significance and impact of the study The identification of the optimal reference gene and analysis of transcription levels of sigma factors in A. caldus can provide clues for reference gene selection and the study of sigma factor function.

Experiments were carried out to examine the oxido-reduction of manganese by extremely acidophilic Acidithiobacillus spp. grown with either elemental sulfur or molecular hydrogen as electron donor. ...

How to recycle metals from the waste resources becomes a hotspot all around the world. Non-ferrous residues, which was produced by non-ferrous melting industry, and various of Cu and Co compounds exist in the residues in the form of CuxOy, CuxSy, CoxSy. In order to efficiently extract valuable metals from the non-ferrous residues, this study investigated the bioleaching behavior of Cu and Co from non-ferrous residues, using iron-oxidizing bacteria (IOB, Leptospirillum ferriphilum CS13) and sulfur-oxidizing bacteria (SOB, Acidithiobacillus caldus S2) by controlling the microbial composition, initial pH, and initial ferrous ion concentration. The results showed that IOB had a better performance on extracting Cu and Co than that of SOB, especially for Cu. Furthermore, 77.7 and 79.8% of Cu and Co were extracted under the optimal ratio of the initial number of IOB and SOB (1:1) after bioleaching, which was more than that when bioleaching by any one of these two kinds of bacteria. However, the changes of initial pH and ferrous ion concentration could not significantly enhance bioleaching performance. The results indicated that bioleaching had a good performance on recovering of metals from non-ferrous residues and excellent application prospect for the cleaner resource recycling.

Phosphate rock containing rare-earth elements (REEs) is considered one of the most promising potential secondary sources of REEs, as evidenced by large tonnages of phosphate rock mined annually. The bioleaching of REEs from phosphate rock using Acidithiobacillus ferrooxidans was done for the first time in this study, and it was found to be greater than abiotic leaching and was more environmentally friendly. The result showed that the total leaching rate of REEs in phosphate rock was 28·46% under the condition of 1% pulp concentration and pH = 2, and the leaching rates of four key rare earths, Y, La, Ce and Nd, were 35·7, 37·03, 27·92 and 32·53% respectively. The bioleaching process was found to be accomplished by bacterial contact and Fe2+ oxidation. The blank control group which contained Fe2+ was able to leach some of the rare earths, indicating that the oxidation of Fe2+ may affect the leaching of rare earths. X-ray diffraction analysis showed that the minerals were significantly altered and the intensity of the diffraction peaks of dolomite and apatite decreased significantly after microbial action compared to the blank control, and it was observed that bacteria adhere to the mineral surface and the minerals become smooth and angular after bioleaching by scanning electron microscope, indicating that bacteria have a further effect on the rock based on Fe2+ oxidation. Finally, Fourier transform infrared spectroscopy and three-dimensional excitation-emission matrix fluorescence spectra analysis showed that extracellular polymeric substances participate in the bioleaching process.

With global demands for mineral resources increasing and ore grades decreasing, microorganisms have been increasingly deployed in biomining applications to recover valuable metals particularly from normally considered waste, such as low-grade ores and used consumer electronics. Acidithiobacillus are a genus of chemolithoautotrophic extreme acidophiles that are commonly found in mining process waters and acid mine drainage, which have been reported in several studies to aid in metal recovery from bioremediation of metal-contaminated sites. Compared to conventional mineral processing technologies, biomining is often cited as a more sustainable and environmentally friendly process, but long leaching cycles and low extraction efficiency are main disadvantages that have hampered its industrial applications. Genetic engineering is a powerful technology that can be used to enhance the performance of microorganisms, such as Acidithiobacillus species. In this review, we compile existing data on Acidithiobacillus species' physiological traits and genomic characteristics, progresses in developing genetic tools to engineer them: plasmids, shutter vectors, transformation methods, selection markers, promoters and reporter systems developed, and genome editing techniques. We further propose genetic engineering strategies for enhancing biomining efficiency of Acidithiobacillus species and provide our perspectives on their future applications.

The potential of Acidithiobacillus (Thiobacillus) genus members, namely Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, for bioleaching purposes is known. Specifically, previous studies have shown the potential of A. thiooxidans strain DSM 26636 used in bioleaching processes to remove metals in high-metal-content matrices. All Acidithiobacillus growth-monitoring techniques available to date, including sulfate production, commonly used, present disadvantages. Thus, the current work shows a technique based on DNA quantification to evaluate the growth of A. thiooxidans DSM 26636, which is useful even in the presence of a high-metal-content residue. This proposed methodology may represent a functional complementary tool to evaluate Acidithiobacillus growth to develop biometallurgical applications.

Acidithiobacillus ferrooxidans ATCC23270 is a gram-negative and autotrophic bacillus acquiring energy via the oxidation of iron and sulfur. The pet II operon is involved in the sulfur metabolism of A. ferrooxidans. However, the mechanisms that control the expression of the pet II operon are poorly understood. We previously described that the AFE2726 protein is associated with the expression of the pet II operon. Here, we attempted to analyze the involvement of AFE2726 in the regulation of pet II operon expression. First, pEGF recombinant vectors driven by the promotor of the pet II operon, denoted pEGF-pet II, were constructed. Then, DH5α E. coli cultures containing the vector mentioned above were cultivated in Na2S2O3, as this medium substantially enhances the expression of green fluorescent proteins. To examine the regulatory effect of AFE2726 on the pet II operon, the C62/V and C72/V mutants for AFE2726 were constructed in pEGF-pet II vectors using the site-directed deletion method. Compared to pEFG-pet II and pEFG-pet II-Δ-C62/V, pEFG-pet II-Δ-C72/V reduced the expression of green fluorescent proteins dramatically when transformed into DH5α E.coli in Na2S2O3 medium. This suggested that the 72nd cysteine was a crucial residue of the AFE2726 protein, affecting the response of the pet II operon to sodium thiosulfate. Furthermore, the binding site of AFE2726 on the promotor of the pet II operon was identified using the electrophoretic mobility shift assay (EMSA), and it was found to be a 34bp inverted repeat sequence (named IR4), which ranged from −65 to −32. In summary, our results indicated that the AFE2726 protein regulates the pet II operon by binding to the IR4 sequence in its promotor region, whose function is likely affected by Na2S2O3 binding to its Cys72 residue counterpart.

Summary 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 the 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 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.

Acidithiobacillus ferrooxidans cells can oxidize iron and sulfur and are key members of the microbial biomining communities that are exploited in the large-scale bioleaching of metal sulfide ores. Some minerals are recalcitrant to bioleaching due to the presence of other inhibitory materials in the ore bodies. Additives are intentionally included in processed metals to reduce environmental impacts and microbially influenced corrosion. We have previously reported a new aerobic corrosion mechanism where A. ferrooxidans cells combined with pyrite and chloride can oxidize low-grade stainless steel (SS304) with a thiosulfate-mediated mechanism. Here we explore process conditions and genetic engineering of the cells that enable corrosion of a higher grade steel (SS316). The addition of elemental sulfur and an increase in the cell loading resulted in a 74% increase in the corrosion of SS316 as compared to the initial sulfur- and cell-free control experiments containing only pyrite. The overexpression of the endogenous rus gene, which is involved in the cellular iron oxidation pathway, led to a further 85% increase in the corrosion of the steel in addition to the improvements made by changes to the process conditions. Thus, the modification of the culturing conditions and the use of rus-overexpressing cells led to a more than threefold increase in the corrosion of SS316 stainless steel, such that 15% of the metal coupons was dissolved in just 2 weeks. This study demonstrates how the engineering of cells and the optimization of their cultivation conditions can be used to discover conditions that lead to the corrosion of a complex metal target.

We have previously proposed a highly efficient technology for metal recovery from low-grade zinc sulfide concentrate by two-step treatment including ferric iron leaching and biooxidation of the produced ferrous iron to ferric iron (an oxidizer for sulfide minerals). The present work proposes joint biooxidation of the products of ferric leaching of the low-grade zinc concentrate: a solution containing 24.2 g/L ferrous iron and a residue containing 29.7% elemental sulfur. Apart from regeneration of the oxidant, joint biooxidation of the solution and the residue by microbial associations including iron- and sulfur-oxidizing organisms, also prevents alkalinization of the solution, which makes it possible to omit using sulfuric acid during bioregeneration. The most efficient bioregeneration of ferric iron occurred when a mixed microbial culture was grown at 40°C. According to the results of metagenomic analysis, predominant lithotrophs in the culture belonged to the genera Leptospirillum, Sulfobacillus, Acidithiobacillus, and Ferroplasma; organotrophic Cuniculiplasma was also present. Under these conditions, the rate of ferrous iron oxidation was 5.4 g/(L day), and the oxidation level of elemental sulfur in the residue was 59.5%. The role of mixo- and organotrophic acidophilic microorganisms is discussed. They predominated in associations during bioregeneration of the oxidant, as well as in the course of the medium detoxication in order to ensure growth of the autotrophic association by utilization of organic compounds. The latter were released by autotrophs during the initial production of the ferric leaching solution and due to autolysis of microbial cells during the high-temperature ferric leaching.

This study aims to investigate the attachment of Acidithiobacillus ferrooxidans to pyrite in two different environments: fresh and saline water (water with 35 g/L of NaCl or 0.6 M). Adsorption isotherms were analyzed using the Langmuir and Freundlich models. Saline water is water with 35 g/L of NaCl (0.6 M), which is the concentration of NaCl in seawater. The use of raw seawater in mining is becoming relevant in leaching and flotation process. At the same time the use of microorganisms in both processes is gaining attention. For this reason, it is important to study the behavior of adherence of microorganisms to minerals in saline aqueous environments, similar to seawater. The bacteria showed a higher level of attachment to pyrite in fresh water than in saline water. The Langmuir model fitted better the experimental data obtained in fresh water than in saline water with a coefficient of determination (R2) of 0.85 and 0.61 for fresh and saline water, respectively. This suggests that the bacteria tend to adhere more as a monolayer in fresh than in saline water in the early stage of adhesion.

Production of conventional fertilizers requires significant energy consumption which increases the price of the product. In recent years, a growing interest on the application of natural products has been shown by public. The aim of this work is to evaluate the effectiveness of the sulfur bacteria Acidithiobacillus thiooxidans to promote mineralogy changes and increase nutrient availability, using phosphate and potassic rocks to produce PK biofertilizers. The study was set up in Petri dishes using 30 g of phosphate rock + 30 g of potassium rock, each rock mixed with elemental sulfur applied at two levels 10% and 20% (3 g and 6 g) in dish. The experiment was conducted in a completely randomized design with eight replications (each rock). The bacterium was inoculated applying 1 ml per g of elemental sulfur. The rocks were incubated during 180 days and mineralogical analysis by XRD and chemical analysis were processed at 30, 60, 120, 150 and 180 days after inoculation. The Acidithiobacillus produced sulfuric acid, which promoted mineralogical changes especially at 180 days after inoculation, compared with the initial time. The inoculation of Acidithiobacillus reduced pH and promoted mineralogical changes in P and K rocks with a significant increase in P and K availability, becoming a viable alternative to plant nutrition instead of soluble PK fertilizers. In addition, it showed great potential for a sustainable agriculture system.

In this work, a method of enhanced packed-bed microbial oxidation-neutralization has been employed to treat Fe

Oxidative dissolution of stibnite (Sb

Submitted by Mario BC (mario@bc.ufrpe.br) on 2022-09-12T12:00:43Z No. of bitstreams: 1 Rita Magally Oliveira da Silva Marcelino.pdf: 751200 bytes, checksum: 265157fe42d6c197a50bf025a3930f30 (MD5) Made available in DSpace on 2022-09-12T12:00:43Z (GMT). No. of bitstreams: 1 Rita Magally Oliveira da Silva Marcelino.pdf: 751200 bytes, checksum: 265157fe42d6c197a50bf025a3930f30 (MD5) Previous issue date: 2022-02-24 The development of crops such as cowpea (Vigna unguiculata (L.) Walp) can be limited by the excess of salts and/or exchangeable sodium in the soils, being necessary the correction of areas that present these problems in order to make them viable for the agriculture. The application of products such as agricultural gypsum are commonly used to reduce salinity, but are not able to contribute to the reduction of soil pH. In this case, it is necessary to use acidifying products such as elemental sulfur, which when associated with bacteria of the genus Acidithiobacillus thiooxidans promotes the reduction of soil pH. The objective of this work was to correct a saline-sodic soil and determine through the use of different conditions: Sulfur, Gypsum, and Sulfur + Gypsum (S, G, S+G), to determine which is the most efficient for the reduction of soil pH. and to enable the increase of soil nutrient contents as a function of the application of different doses of biofertilizer (BNPK) inoculated or not with Bradyrhizobium (BR3267). The study was carried out in a greenhouse at the Universidade Federal Rural de Pernambuco in Recife PE, using a Fluvic Saline-Sodium Neosol collected (0-20 cm) in the region of Ibimirim-PE. A completely randomized design (DIC) was used in a 3x3x2 + 1 factorial scheme, where the interactions between 3 types of conditioning (sulfur + A. thiooxidans; gypsum; sulfur + A. thiooxidans + gypsum), 3 doses of BNPK (50 , 100 and 150% of the recommended dose of N for the cowpea crop, taking into account the soil analysis), in the absence and presence of Bradyrhizobium sp. (BR 3267), with a control treatment (soil only), 3 replications, totaling 57 experimental plots. Each experimental plot consisted of a pot (6 kg of soil) with a cowpea plant. The development of the experiment consisted of the application of the conditioners for 45 days, followed by the application of a leaching depth, corresponding to three times the total volume of soil pores. Then, the fertilization of the biofertilizer with different doses was carried out and the sowing of cowpea inoculated or not with Bradyrhizobium. The application of the conditioner S + A. thiooxidans provided the soil with a reduction in the pH value of the soil, when associated with the application of leaching depth, this conditioner also contributes to the reduction of exchangeable sodium in the soil. In addition, the incorporation of high doses of BNPK contributed to the increment of nutrients in the soil such as K, Ca and Mg. The inoculation of Bradyrhizobium associated with BNPK influenced the number of nodules, the growth of cowpea and the accumulation of nitrogen in the shoot. O desenvolvimento de culturas como o feijão-caupi (Vigna unguiculata (L.) Walp) pode ser limitado pelo excesso de sais e/ou sódio trocável nos solos, sendo necessária a correção de áreas que apresentem esses problemas objetivando torná-las viáveis para a agricultura. A aplicação de produtos como o gesso agrícola são comumente utilizados para reduzir a salinidade, mas não são capazes de contribuir para a redução do pH do solo. Neste caso se faz necessário o uso de produtos acidificantes como o enxofre elementar, que quando associado a bactéria do gênero Acidithiobacillus thiooxidans promove a redução do pH do solo. O trabalho teve como objetivo corrigir um solo salino-sódico e determinar através do uso de diferentes condicionantes: Enxofre, Gesso e Enxofre + Gesso (S, G, S+G), qual o mais eficiente para a redução do pH do solo e possibilitar o aumento dos teores de nutrientes no solo em função da aplicação de diferentes doses do biofertilizante (BNPK) inoculados ou não com Bradyrhizobium (BR3267). O estudo foi realizado em casa de vegetação na Universidade Federal Rural de Pernambuco em Recife PE, utilizando um Neossolo Flúvico salino-sódico coletado (0-20 cm) na região de Ibimirim-PE. Utilizou-se delineamento inteiramente casualizado (DIC) em esquema fatorial 3x3x2 + 1, onde foram avaliadas as interações entre 3 tipos de condicionantes (enxofre + A. thiooxidans; gesso; enxofre + A. thiooxidans + gesso), 3 doses de BNPK (50, 100 e 150% da dose recomendada de N para a cultura do feijão-caupi, levando em consideração a análise do solo), na ausência e presença de Bradyrhizobium sp. (BR 3267), com um tratamento controle (apenas o solo), 3 repetições, totalizando 57 parcelas experimentais. Cada parcela experimental foi constituída por um vaso (6 kg de solo) com uma planta de feijão-caupi. O desenvolvimento do experimento consistiu na aplicação dos condicionantes durante 45 dias, seguidos da aplicação de lâmina de lixiviação, correspondente a três vezes o volume total de poros do solo. Em seguida realizou-se a adubação do biofertilizante com diferentes doses e o semeio do feijão-caupi inoculados ou não com Bradyrhizobium. A aplicação do condicionante S + A. thiooxidans proporcionou ao solo redução do valor de pH do solo, quando associado a aplicação de lâmina de lixiviação, esse condicionante contribui também para a redução de sódio trocável no solo. Além disso, a incorporação de doses elevadas do BNPK contribuiu para o incremento de nutrientes no solo como K, Ca e Mg. A inoculação de Bradyrhizobium associado ao BNPK influenciou no número de nódulos, no crescimento do feijão-caupi e no acúmulo de nitrogênio na parte aérea.

Biological desulfurization plays an increasingly important role in desulfurization industry. A strain of

The MarR family, as multiple antibiotic resistance regulators, is associated with the resistance of organisms to unfavorable conditions. MarR family extracellular polymeric substances (EPS)-associated transcriptional regulator (EpsR

Bundesanstalt fur Geowissenschaften und Rohstoffe GEOS Centro de Tecnologia Mineral CPRM Landesamt fur Bergbau Brasilian Nickel PLC Natural History Museum 2027-12

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A group of particular acidophiles microorganisms (bacteria and archaea) known as chemolithoautotrophs are capable of using minerals as fuel. Its oxidation generates electrons to obtain energy and carbon that is obtained by fixing CO2 from the air. During this aerobic mineral oxidation, metals are solubilized or biodegraded. Metal bioleaching usually is used in biomining and urban biomining approaches to recovery metals such as copper, gold and zinc. Several species of bacterial genus Acidithiobacillus display a great bioleaching activity. Bacterial attachment and biofilm formation are the initial requirements to begin a successful bioleaching process. Biofilm formation in Acidithiobacillus bacteria is strongly regulated by cell to cell communication system called Quorum Sensing. The goal of this chapter is to review the Quorum Sensing system mediated by the autoinducer N-acyl- homoserine-lactones in the Bacterium Acidiothiobacillus ferroxidans, in order to enhance and to boost the bioleaching technologies based in the use of this bacterium. The main applications of the cell-to-cell communication system concepts in A. ferrooxidans are reviewed in this chapter. It is that the addition of synthetic autoinducers molecules, which act as agonist of quorum sensing system, especially those with long acyl chains, both as single molecules (C12-AHL, 3-hydroxy-C12-AHL, C14-AHL, and 3-hydroxy-C14-AHL) or as a mixture (C14-AHL/3- hydroxy-C14-AHL/3-oxo-C14-AHL) increased the adhesion to sulfur and pyrite and enhance the metal bioleaching in urban biomining approaches.

Harmful chemicals present in electric vehicle Li-ion batteries (EV LIBs) can limit the pulp density of bioleaching processes using Acidithiobacillus sp. to 1.0% (w/v) or lower. The strong enhancing mechanisms of extracellular polymeric substances (EPS) on the bioleaching of metals from spent EV LIBs at high pulp density (4% w/v) were studied using bio-chemical, spectroscopic, surface structure imaging and bioleaching kinetic methods. Results demonstrated that the added EPS significantly improved bioleaching efficiency of Ni, Co and Mn improved by 42%, 40% and 44%, respectively. EPS addition boosted the growth of cells under adverse conditions to produce more biogenic H

Most studies conducted have focused on the pulp density, Fe3+ concentration and sulfuric acid concentration, etc., of bio-oxidation, and few have reported on the influence of different bio-oxidation methods on kinetics. In this study, a comparative investigation on refractory gold concentrate by batch and continuous bio-oxidation was conducted, with the purpose of revealing the kinetics influence. The results showed that improving the removal rates of the gold-bearing pyrite (FeS2) and arsenopyrite (FeAsS) yielded the best results for increasing gold recovery. The removal rates of S, Fe and relative gold recovery linearly increased when compared to the second-order equation increase of the As removal rate in both batch and continuous bio-oxidation processes. The removal kinetics of S and Fe by continuous bio-oxidation was 12.02% and 12.17% per 24 h day, approximately 86.64% and 51.18% higher than batch bio-oxidation, respectively. The higher removal kinetics of continuous bio-oxidation resulted from a stepwise increase in microbe growth, a larger population and higher dissolved Fe3+ and H2SO4 concentration compared to a linear increase by batch bio-oxidation. The cyanidation gold recovery was as high as 94.71% after seven days of continuous bio-oxidation, with the gold concentrate sulfur removal rates of 83.83%; similar results will be achieved after 13 days by batch bio-oxidation. The 16sRNA sequencing showed seven more microbe cultures in the initial residue than Acid Mine Drainage (AMD) at genus level. The quantitative real-time Polymerase Chain Reaction (PCR) test showed the four main functional average microbe populations of Acidithiobacillus, Leptospirillum, Ferroplasma and Sulfobacillus in continuous bio-oxidation residue as 1.08 × 103 higher than in solution. The multi-microbes used in this study have higher bio-oxidation activity and performance in a highly acidic environment since some archaea co-exist and co-contribute.

Bioleaching of tannery sludge is an efficient and environmentally friendly way for chromium (Cr) removal, which supports the sustainable development of the leather industry. Acidithiobacillus thiooxidans has been reported effective in Cr bioleaching of tannery sludge. However, little is known about whether the presence of other benefiting species could further improve the Cr leaching efficiency of A. thiooxidans. Here, we studied the enhancing roles of four species namely Acidiphilium cryptum, Sulfobacillus acidophilus, Alicyclobacillus cycloheptanicus, and Rhodotorula mucilaginosa in chromium bioleaching of tannery sludge with A. thiooxidans by batch bioleaching experiments. We found that each of the four species facilitated the quick dominance of A. thiooxidans in the bioleaching process and significantly improved the bioleaching performance including bioleaching rate and efficiency. The bioleaching efficiency of Cr in the tannery sludge could reach 100% on the sixth day by co-inoculating A. thiooxidans and four auxiliary species. The achievements shed a light on the role of the community-level interactions on bioleaching and may also serve as guidance for managing bioleaching consortiums for better outcomes.

Acidithiobacillus ferrooxidans is an iron-oxidizing chemolithotroph used for bioleaching of precious metals and is also regarded as a potential host for bioelectrochemical production of value-added chemicals. Despite its industrial utility, however, it is difficult to genetically engineer A. ferrooxidans due to low transformation and recombination efficiencies. Here, we developed a clustered regularly interspaced short palindromic repeats interference (CRISPRi) system that can selectively repress the expression of a target gene in A. ferrooxidans. The mutated gene encoding a nuclease-deactivated Cas9 protein was cloned into the broad-host-range plasmid pBBR1-MCS2, and the applicability of the CRISPRi system was examined using the nitrogenase nifH gene as a knockdown target. Introduction of the CRISPRi plasmid into A. ferrooxidans resulted in decreased nifH transcription and retarded cell growth in the absence of nitrogen sources, demonstrating that the CRISPRi system altered the phenotype of this bacterium via selective gene knockdown. We suggest that the CRISPRi system developed in this study provides an efficient technique for constructing A. ferrooxidans knockdown mutants that are useful for the genetic dissection of this bacterium.

A magnetosome-producing bacterium Acidithiobacillus ferrooxidans BYM (At. ferrooxidans BYM) was isolated and magnetically screened. The magnetosome yield from 0.5896 to 13.1291 mg/g was achieved under different aeration rates, ferrous sulfate, ammonium sulfate, and gluconic acid concentrations at 30 ℃. TEM observed 6–9 magnetosomes in size of 20–80 nm irregularly dispersed in a cell. STEM-EDXS and HRTEM-FFT implied that the elongated-prismatic magnetite magnetosomes with {110} crystal faces grown along the [111] direction. Whole-genome sequencing and annotation of BYM showed that 3.2 Mb chromosome and 47.11 kb plasmid coexisted, and 322 genes associated with iron metabolism were discovered. Ten genes shared high similarity with magnetosome genes were predicted, providing sufficient evidence for the magnetosome-producing potential of BYM. Accordingly, we first proposed a hypothetic model of magnetosome formation including vesicle formation, iron uptake and mineralization, and magnetite crystal maturation in At. ferrooxidans. These indicated that At. ferrooxidans BYM would be used as a commercial magnetosome-producing microorganism.

In the subsurface, the interplay between microbial communities and the surrounding mineral substrate, potentially used as an energy source, results in different mineralized structures. The molecular composition of such structures can record and preserve information about the metabolic pathways that have produced them. To characterize the molecular composition of the subsurface biosphere, we have analyzed some core samples by time-of-flight secondary ion mass spectrometry (ToF-SIMS) that were collected in the borehole BH8 during the operations of the Mars Analog and Technology Experiment (MARTE) project. The molecular analysis at a micron-scale mapped the occurrence of several inorganic complexes bearing PO3-, SOx(2to4)-, NOx(2,3)-, FeOx(1,2)- SiO2-, and Cl-. Their distribution correlates with organic molecules that were tentatively assigned to saturated and monounsaturated fatty acids, polyunsaturated fatty acids, saccharides, phospholipids, sphingolipids, and potential peptide fragments. SOx- appear to be mineralizing some microstructures larger than 25 microns, which have branched morphologies, and that source SO3-bearing adducts. PO3-rich compounds occur in two different groups of microstructures which size, morphology, and composition are different. While a group of >40-micron sized circular micronodules lacks organic compounds, an ovoidal microstructure is associated with m/z of other lipids. The NO2-/NO3- and Cl- ions occur as small microstructure clusters (, Fundo de Desenvolvimento das Cientifico e da Tecnologia da RAE de Macau (proposals FDCT-0005-2020-A1 and FDCT-18-024-SSI), and the project on Civil Aerospace Technologies No. D020303 funded by China National Space Administration and NRA-02-OSS-01 NASAASTEP ‘‘Mars Astrobiology Research and Technology Experiment (MARTE),’’

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. producing sulfuric acid and ferric iron have been investigated for several decades in the bioleaching of metal-containing ores. Their application has now been extended to the extraction of metals from artificial ores and other secondary sources. In this study, an optimized process for producing biogenic sulfuric acid from elemental sulfur by two sulfur-oxidizing species, A. thiooxidans and A. caldus and their combinations, was investigated in batch and stirred tank experiments. Using a combined culture of both species, 1.05 M and 1.4 M biogenic sulfuric acid was produced at 30 °C and 6% elemental sulfur in batch and semi continuous modes, respectively. The acid produced was then used to control the pH in a heap bioleaching system in which iron- and sulfur-oxidizing A. ferrooxidans was applied to biologically leach metals from waste incineration residuals. Metals like Cu, Ni, Al, Mn, and Zn were successfully recovered by 99, 93, 84, 77 and 68%, respectively within three weeks of heap bioleaching. Overall, a potential value recovery of incorporated metals70% could be achieved. This highlights the potential and novelty of applying extremely acidophilic sulfur-oxidizing bacteria for cheap and efficient production of biogenic sulfuric acid and its use in pH control.

Genetically encoded biosensors based on engineered fluorescent proteins (FPs) are essential tools for monitoring the dynamics of specific ions and molecules in biological systems. Arsenic ion in the +3 oxidation state (As3+) is highly toxic to cells due to its ability to bind to protein thiol groups, leading to inhibition of protein function, disruption of protein–protein interactions, and eventually to cell death. A genetically encoded biosensor for the detection of As3+ could potentially facilitate the investigation of such toxicity both in vitro and in vivo. Here, we designed and developed two prototype genetically encoded arsenic biosensors (GEARs), based on a bacterial As3+ responsive transcriptional factor AfArsR from Acidithiobacillus ferrooxidans. We constructed FRET-based GEAR biosensors by insertion of AfArsR between FP acceptor/donor FRET pairs. We further designed and engineered single FP-based GEAR biosensors by insertion of AfArsR into GFP. These constructs represent prototypes for a new family of biosensors based on the ArsR transcriptional factor scaffold. Further improvements of the GEAR biosensor family could lead to variants with suitable performance for detection of As3+ in various biological and environmental systems.

Using acidophilic bacteria to catalyze the reductive dissolution of oxidized minerals is an innovative process that facilitates the extraction of valuable base metals (principally cobalt and nickel) from limonites, which are otherwise often regarded as waste products of laterite mining. The most appropriate conditions required to optimize reductive mineral dissolution are unresolved, and the current work has reassessed the roles of Acidithiobacillus spp. in this process and identified novel facets. Aerobic bio-oxidation of zero-valent sulfur (ZVS) can generate sufficient acidity to counterbalance that consumed by the dissolution of oxidized iron and manganese minerals but precludes the development of low redox potentials that accelerate the reductive process, and although anaerobic oxidation of sulfur by iron-reducing species can achieve this, less acid is generated. Limited reduction of soluble iron (III) occurs in pure cultures of Acidithiobacillus spp. (Acidithiobacillus thiooxidans and Acidithiobacillus caldus) that do not grow by iron respiration. This phenomenon (“latent iron reduction”) was observed in aerated cultures and bioreactors and was independent of electron donor used (ZVS or hydrogen). Sufficient ferrous iron was generated in the presence of sterilized hydrophilic sulfur (bio-ZVS) to promote the effective reductive dissolution of Mn (IV) minerals in limonite and the solubilization of cobalt in the absence of viable acidophiles.

Acidithiobacillus ferrooxidans are well-studied iron- and sulfur-oxidizing acidophilic chemolithoautotrophs that are exploited for their ability to participate in the bioleaching of metal sulfides. Here, we overexpressed the endogenous glutamate--cysteine ligase and glutathione synthetase genes in separate strains and found that glutathione synthetase overexpression increased intracellular glutathione levels. We explored the impact of pH on the halotolerance of iron oxidation in wild type and engineered cultures. The increase in glutathione allowed the modified cells to grow under salt concentrations and pH conditions that are fully inhibitory to wild type cells. These results indicate that glutathione overexpression can be used to increase halotolerance in A. ferrooxidans and would likely be a useful strategy on other acidophilic bacteria.ImportanceThe use of acidophilic bacteria in the hydrometallurgical processing of sulfide ores can enable many benefits including the potential reduction of environmental impacts. The cells involved in bioleaching tend to have limited halotolerance, and increased halotolerance could enable several benefits, including a reduction in the need for fresh water resources. We show that the genetic modification of A. ferrooxidans for the overproduction of glutathione is a promising strategy to enable cells to resist the oxidative stress that can occur during growth in the presence of salt.

A chemolithotrophic bacterium was isolated from sulfur hot spring. According to phenotypic traits and 16-23S rDNA intergenic spacer region analysis, the isolate was identified and named as Acidithiobacillus sp. MR39, which was a gram-negative, rod- shape and non-motile bacterium. The strain was able to grow in a synthetic liquid medium supplemented with the mineral ore as the source of energy. The optimum conditions were found to be within initial pH range of 2.0-2.5, at 34±1˚C and with shaking at 120 rpm. The bacterium had a remarkable potential for mineralization of 88% iron, 75% copper, 59% zinc, 59% nickel and 40% cobalt upon their growth in the liquid media. After adapting the bacterial cells to copper ions in 100 mM for 5-day incubation, biorecovery of Cu increased about 10% comparing to unadapted cells that are able to dissolve approximately 15% of total cu of mineral concentrate. Considering the finding in this study, the strain MR39 offers a great prospect for in situ extraction of metals from various ores along with other indigenous bacteria that can grow under ambient conditions.

The semi-pilot scale bioleaching of electroplating sludge by the moderately thermophilic acidophilic consortium was carried out for the first time. During the microbial cultivation, Leptospirillum ferriphilum CS13, Acidithiobacillus caldus S2, and Sulfobacillus acidophilus CS5 could grow rapidly in a 300 L aeration packed reactor, in which the total suspended cell concentration could fluctuate around 3 × 108 cells/mL and the community structure remained relatively stable. During the bioleaching process, the microbial stock solution could effectively leach heavy metals from electroplating sludge in a stirred reactor within a few hours. Meanwhile, the effects of pH, temperature, the quantity of active culture, and liquid-solid ratio on the bioleaching behavior were also investigated. The optimal conditions for electroplating sludge bioleaching were pH 1.5, temperature 45 °C, bacterial liquid ratio 40%, liquid-solid ratio 4:1 L kg−1, and leaching time 5 h. The total removal rate of various heavy metals in electroplating sludge was over 99%. The bioleaching residue was successfully passed the TCLP test, and the total contents of heavy metals in the residue were also well below the regulatory criteria. In addition, the XRD analysis of the bioleaching residue was also confirmed that the moderately thermophilic consortium bioleaching provided a cleaner process than chemical leaching on the removal of the residual fraction metals, which was feasible and attractive for industrial treatment of electroplating sludge.

The low bioleaching efficiency of Acidithiobacillus ferrooxidans results in its sparse industrial application for metal extraction from waste printed circuit boards (WPCBs). To improve the bioleaching efficiency of Acidithiobacillus ferrooxidans, we propose the use of mechanical activation to dispose WPCBs prior to performing bioleaching. Response surface methodology (RSM), scanning electron microscope- energy dispersive spectrometer (SEM-EDS), and laser particle size analyzer (LPSA) were used to optimize and analyze the mechanical activation process, respectively. The optimal conditions for mechanical activation was a milling time of 2 h, milling speed of 340 r min−1, and ball material ratio (w/w) of 10/1; the bioleaching rates of Cu, Ni, and Zn were 94.33%, 90.69%, and 90.78%, respectively. The bioleaching rates of Cu, Ni, and Zn were 74.75%, 70.46%, and 71.05%, respectively, without mechanical activation pretreatment. SEM-EDS and LPSA analyses indicated that mechanical activation could lead to a smaller particle size and expose wrapped metals, thus improving the bioleaching efficiency oyf tyhe metals inside the WPCBs. The electrode potential of the metals was likely changed by the mechanical activation, resulting in an improvement of their bioleaching efficiency. Additionally, the bioleaching rates of Pb, Cr, and Cd after mechanical activation pretreatment were 10.29%, 74.89%, and 54.12%, respectively. Contrastingly, the bioleaching rates of Pb, Cr, and Cd without mechanical activation pretreatment were 5.18%, 59.97%, and 37.12%, respectively. Thereinto, the precipitation of PbSO4 may result in a decrease of leached Pb. We propose a mechanical activation process for improving the bioleaching efficiency of metals from WPCBs.

A biotrickling filter (BTF) inoculated with concentrated activated sludge possessing highly efficient degrading strains was investigated on a pilot-scale for the treatment of viscose fibre waste gas containing carbon disulfide (CS2) and hydrogen sulfide (H2S). The BTF had a quick start-up period, with 90.6% and 98.2% removal of CS2 and H2S, respectively, from the 18th day of acclimation. When the influent concentration was increased from 145 mg m−3 to 1912 mg m−3, steady removal efficiencies (REs) of above 70% for CS2 and 90% for H2S were achieved for the entire operation, with maximum elimination capacities (ECs) of 122.7 g m−3 h−1and 108.2 g m−3 h−1 for CS2 and H2S, respectively. The results showed that H2S was preferentially degraded by BTF, owing to hydrophilic H2S having a low Henry coefficient, which allowed it to adsorb on the biofilm surface more easily and made its biodegradation more favorable. The pH significantly affected the REs of CS2 and H2S, which decreased from 81% to 52% and from 95% to 73%, respectively, with a pH increase from 2 to 8, while sulfate accumulation did not significantly affect the pollutant REs. A tolerance experiment showed that BTF was resistant to large fluctuations in CS2 and H2S concentrations, with a RE of 80% recovered in only 2 days. Microbial diversity analysis showed that Acidithiobacillus, Acidiphilium, and Metallibacterium had higher relative abundances at the genus level, and remained persistent throughout the operation, implying that these strains played an important role in the simultaneous removal of CS2 and H2S from waste gas.

The genus Acidithiobacillus currently includes seven species with validly published names, which fall into two major groups, those that can oxidize ferrous iron and those that do not. All seven species can use zero-valent sulfur and reduced sulfur oxy-anions as electron donors, are obligately chemolithotrophic and acidophilic bacteria with pH growth optima below 3.0. The 16S rRNA gene of a novel strain (CJ-2T) isolated from circum-neutral pH mine drainage showed 95–97 % relatedness to members of the genus Acidithiobacillus . Digital DNA–DNA hybridization (dDDH) values between strains and whole-genome pairwise comparisons between the CJ-2T strain and the reference genomes available for members of the genus Acidithiobacillus confirmed that CJ-2Trepresents a novel species of this genus. CJ-2T is a strict aerobe, oxidizes zero-valent sulfur and reduced inorganic sulfur compounds but does not use ferrous iron or hydrogen as electron donors. The isolate is mesophilic (optimum growth temperature 25–28 °C) and extremely acidophilic (optimum growth pH 3.0), though its pH optimum and maximum were significantly higher than those of non-iron-oxidising acidithiobacilli with validly published names. The major fatty acids of CJ-2T were C18 : 1ω7c, C:16 : 1ω7c/iso-C15 : 0 2-OH, C16 : 0 and C19 : 0 cyclo ω8c and the major respiratory quinone present was Q8. The name Acidithiobacillus sulfuriphilus sp. nov. is proposed, the type strain is CJ-2T (=DSM 105150T=KCTC 4683T).

Acidithiobacillus ferrooxidans, a chemolithoautotrophic bacterium, is well known for its mineral oxidizing properties. The current study combines experimental and whole genome sequencing approaches to investigate an iron oxidizing, extreme acidophilic bacterium, A. ferrooxidans isolate (IO-2C) from an acid seep area near Carlos, TX, USA. Strain IO-2C was capable of oxidizing iron i.e. iron sulphate and iron ammonium sulphate yielding shwertmannite and jarosite minerals. Further, the bacterium’s genome was sequenced, assembled and annotated to study its general features, structure and functions. To determine genetic heterogeneity, it was compared with the genomes of other published A. ferrooxidans strains. Pan-genome analysis displayed low gene conservation and significant genetic diversity in A. ferrooxidans species comprising of 6926 protein coding sequences with 23.04% (1596) core genes, 46.13% (3195) unique and 30.82% (2135) accessory genes. Variant analysis showed >75,000 variants, 287 of them with a predicted high impact, in A. ferrooxidans IO-2C genome compared to the reference strain, resulting in abandonment of some important functional key genes. The genome contains numerous functional genes for iron and sulphur metabolism, nitrogen fixation, secondary metabolites, degradation of aromatic compounds, and multidrug and heavy metal resistance. This study demonstrated the bio-oxidation of iron by newly isolated A. ferrooxidans IO-2C under acidic conditions, which was further supported by genomic analysis. Genomic analysis of this strain provided valuable information about the complement of genes responsible for the utilization of iron and tolerance of other metals.