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Variations in water availability represent a foremost stress factor affecting the growth and survival of microorganisms. Acidophilic bioleaching bacteria are industrially applied for releasing metals from mineral sulphides, and they are considered extremely tolerant to oxidative conditions prevailing in acidic bioleaching environments. Such processes usually are performed in heaps and thus these microorganisms are also exposed to intermittent desiccations or high osmolarity periods that reduce the water availability. However, the tolerance to water stress and the molecular basis of adaptation to it are still largely unknown. The aim of this work was to determine the cellular response to desiccation stress and establish its relationship to oxidative stress response in the acidophilic iron-oxidizing bacteria Acidithiobacillus ferrooxidans ATCC 23270 and Leptospirillum ferriphilum DSM 14647. Results showed that the exposure of cell cultures to desiccation (0–120 min) led to a significant reduction in cell growth, and to an increase in content in reactive oxygen species in both bacteria. However, Leptospirillum ferriphilum turned out to be more tolerant than Acidithiobacillus ferrooxidans. In addition, the pre-treatment of the cell cultures with compatible solutes (trehalose and ectoine), and antioxidants (glutathione and cobalamin) restored all stress parameters to levels exhibited by the control cultures. To evaluate the role of the osmotic and redox homeostasis mechanisms in coping with desiccation stress, the relative expression of a set of selected genes was approached by RT-qPCR experiments in cells exposed to desiccation for 30 min. Results showed a generalized upregulation of genes that code for mechanosensitive channels, and enzymes related to the biosynthesis of compatible solutes and oxidative stress response in both bacteria. These data suggest that acidophiles show variable tolerance to desiccation and allow to establish that water stress can trigger oxidative stress, and thus anti-oxidative protection capability can be a relevant mechanism when cells are challenged by desiccation or other anhydrobiosis states. • Acidophilic bacteria At. ferrooxidans and L. ferriphilum can tolerate desiccation and resume growth after re-hydration. • Desiccation leads to an increase in the intracellular content of reactive oxygen species (ROS). • The exogenous supplementation of antioxidants allows the growth´s recovery of cell cultures after exposure to desiccation. • The supplementation of compatible solutes allows the growth´s recovery of cell cultures after exposure to desiccation. • Desiccation stress leads to an increase in transcript levels of genes related to osmotic and redox balance. [ABSTRACT FROM AUTHOR]

PCBs are mainly treated by pyrometallurgy to recover valuable metals. However pyrometallurgy is high energy-cost process and due to presence of plastics in PCBs causes the emission of toxic compounds. Therefore, the development of environmentally friendly, cost- and energy-efficient new processes for efficient metal recovery from PCBs is of particular important. From this point of view bioleaching is considered as a novel promising approach for metal mobilization from various secondary raw materials and wastes. Bioleaching experiments were performed using Leptospirillum ferriphilum CC in the following modes: PCBs were added simultaneously with inoculum, after 24 and 48 hours of cultivation of in order to enhance efficiency of copper recovery. From data obtained it can be concluded that optimal condition for copper recovery is the set of experiment when PCBs were added simultaneously with inoculation of L. ferriphillum CC. The maximum rate of dissolution of copper (0.120 g/L h) was observed in this mode of the experiment. Besides both the higher dissolution rate and larger amount of copper is observed at 2.5 % of PD. [ABSTRACT FROM AUTHOR]

A strain of Leptospirillum sp. CC previously isolated from Akhtala polymetallic ore (Armenia) was studied. The main morphological and physiological characteristics of CC were revealed. The optimal growth temperature was 40 °C and optimal pH 1.5. A phylogenetic analysis based on 16S rRNA gene sequences (GenBank ID OM272948) showed that isolate CC was clustered with L. ferriphilum and possessed 99.8% sequence similarity with the strain L. ferriphilum OL12-2 (KF356024). The molar fraction of DNA (G + C) of the isolate was 58.5%. Bioleaching experiment indicates that L. ferriphilum CC can oxidize Fe(II) efficiently, and after 17 days, 44.1% of copper and 91.4% of iron are extracted from chalcopyrite and pyrite, respectively. The efficiency of L. ferriphilum CC in pyrite oxidation increases 1.7 times when co-cultivated with At. ferrooxidans ZnC. However, the highest activity in pyrite oxidation shows the association of L.ferriphilum CC with heterotrophic Acidocella sp. RBA bacteria. It was shown that bioleaching of copper and iron from chalcopyrite by association of L. ferriphilum CC, At. ferrooxidans ZnC, and At. albertensis SO-2 in comparison with pure culture L. ferriphilum CC for 21 days increased about 1.2 and 1.4–1.6 times, respectively. [ABSTRACT FROM AUTHOR]

• New method is proposed for measuring dissolved oxygen concentration. • DO concentration is determined in high iron concentrations and low pH solutions. • DO was measured using ferrous iron oxidation as an indicator with redox potential. Iron sulfate solutions and the extremophile lifeforms that can live within them are industrially and environmentally important in many applications and require proper assessments of solution properties. Determination of saturated dissolved oxygen concentration is an important parameter for monitoring iron biooxidation processes. However, its determination is not so straight forward using commercially available dissolved oxygen meters. Such meters utilize internal calculation models based on the saline properties of seawater which can be easily overlooked. A method for determination of the saturated dissolved oxygen concentration in acidic iron sulfate solutions with the inclusion of other inorganic salts is proposed in this work using the biooxidation of ferrous iron as an indicator measured with redox potential and converted to oxygen concentration through bioreaction stoichiometry. The technique was tested on a BioGenerator system over the course of four days and proved satisfactory in establishing a value for the saturated dissolved oxygen concentration of the bioreactor broth. Study of the lifespan properties of the microorganisms in absence of ferrous iron substrate was briefly examined to determine the effective handling period of solutions for assessment. [ABSTRACT FROM AUTHOR]

The bioleaching of manganese present in mining waste after metal extraction can be catalyzed by Leptospirillum (L.) ferriphilum by allowing atmospheric carbon dioxide to be used in this autotrophic process and generating the subsequent recovery of silver. Bioleaching of metals is widely performed in agitated tanks; therefore, it is important to assess the mass transfer capacity of gaseous substrates, such as carbon dioxide, during the microbial processes. The main objective of this research was to evaluate the effects of the presence and concentration of a transfer vector (silicone oil) added into a stirred-tank bioreactor during bioleaching of mining tailings catalyzed by L. ferriphilum, determined by the combined gas/oil mass transfer coefficient of carbon dioxide (kLaCO2) into the aqueous phase. The experiments were carried out following a Box–Behnken experimental design, evaluating the concentrations of mining waste (30%, 40%, and 50%), Fe2+, serving as electron donor (2, 8, and 14 g/L), and silicon oil (0%, 5%, and 10%). A significant increase in kLaCO2 was observed after the addition of the transfer vector by comparing the lowest kLaCO2 value of 1.68 h−1 (obtained at 50% pulp, 8 g/L Fe2+, and 0% silicone oil) and the highest kLaCO2 of 21.81 h−1 (obtained at 30% pulp, 2 g/L Fe2+, 5% silicone oil). The results showed statistically significant differences in the transfer of carbon dioxide during the bioleaching process with a transfer vector. [ABSTRACT FROM AUTHOR]

A strain of Leptospirillum sp. CC previously isolated from Akhtala polymetallic ore (Armenia) was studied. The main morphological and physiological characteristics of CC were revealed. The optimal growth temperature was 40 °C and optimal pH 1.5. A phylogenetic analysis based on 16S rRNA gene sequences (GenBank ID OM272948) showed that isolate CC was clustered with L. ferriphilum and possessed 99.8% sequence similarity with the strain L. ferriphilum OL12-2 (KF356024). The molar fraction of DNA (G + C) of the isolate was 58.5%. Bioleaching experiment indicates that L. ferriphilum CC can oxidize Fe(II) efficiently, and after 17 days, 44.1% of copper and 91.4% of iron are extracted from chalcopyrite and pyrite, respectively. The efficiency of L. ferriphilum CC in pyrite oxidation increases 1.7 times when co-cultivated with At. ferrooxidans ZnC. However, the highest activity in pyrite oxidation shows the association of L.ferriphilum CC with heterotrophic Acidocella sp. RBA bacteria. It was shown that bioleaching of copper and iron from chalcopyrite by association of L. ferriphilum CC, At. ferrooxidans ZnC, and At. albertensis SO-2 in comparison with pure culture L. ferriphilum CC for 21 days increased about 1.2 and 1.4–1.6 times, respectively.

Bioleaching is a promising strategy to recover valuable metals from spent printed circuit boards (PCBs). The performance of the process is catalyzed by microorganisms, which the toxic effect of PCBs can inhibit. This study aimed to investigate the capacity of an acidophilic iron-oxidizing culture, mainly composed of Leptospirillum ferriphilum, to oxidize iron in PCB-enriched environments. The culture pre-adapted to 1% (w/v) PCB content successfully thrived in leachates with the equivalent of 6% of PCBs, containing 8.5 g L–1 Cu, 8 g L–1 Fe, 1 g L–1 Zn, 92 mg L–1 Ni, 12.6 mg L–1 Pb, and 4.4 mg L–1 Co, among other metals. However, the inhibiting effect of PCBs limited the microbial activity by delaying the onset of the exponential iron oxidation. Successive subcultures boosted the activity of the culture by reducing this delay by up to 2.6 times under batch conditions. Subcultures also favored the rapid establishment of high microbial activity in continuous mode.

Bioleaching is a promising strategy to recover valuable metals from spent printed circuit boards (PCBs). The performance of the process is catalyzed by microorganisms, which the toxic effect of PCBs can inhibit. This study aimed to investigate the capacity of an acidophilic iron-oxidizing culture, mainly composed of Leptospirillum ferriphilum , to oxidize iron in PCB-enriched environments. The culture pre-adapted to 1% (w/v) PCB content successfully thrived in leachates with the equivalent of 6% of PCBs, containing 8.5 g L–1 Cu, 8 g L–1 Fe, 1 g L–1 Zn, 92 mg L–1 Ni, 12.6 mg L–1 Pb, and 4.4 mg L–1 Co, among other metals. However, the inhibiting effect of PCBs limited the microbial activity by delaying the onset of the exponential iron oxidation. Successive subcultures boosted the activity of the culture by reducing this delay by up to 2.6 times under batch conditions. Subcultures also favored the rapid establishment of high microbial activity in continuous mode. [ABSTRACT FROM AUTHOR]

The bioleaching of manganese present in mining waste after metal extraction can be catalyzed by Leptospirillum (L.) ferriphilum by allowing atmospheric carbon dioxide to be used in this autotrophic process and generating the subsequent recovery of silver. Bioleaching of metals is widely performed in agitated tanks; therefore, it is important to assess the mass transfer capacity of gaseous substrates, such as carbon dioxide, during the microbial processes. The main objective of this research was to evaluate the effects of the presence and concentration of a transfer vector (silicone oil) added into a stirred-tank bioreactor during bioleaching of mining tailings catalyzed by L. ferriphilum, determined by the combined gas/oil mass transfer coefficient of carbon dioxide (kLaCO2) into the aqueous phase. The experiments were carried out following a Box–Behnken experimental design, evaluating the concentrations of mining waste (30%, 40%, and 50%), Fe2+, serving as electron donor (2, 8, and 14 g/L), and silicon oil (0%, 5%, and 10%). A significant increase in kLaCO2 was observed after the addition of the transfer vector by comparing the lowest kLaCO2 value of 1.68 h−1 (obtained at 50% pulp, 8 g/L Fe2+, and 0% silicone oil) and the highest kLaCO2 of 21.81 h−1 (obtained at 30% pulp, 2 g/L Fe2+, 5% silicone oil). The results showed statistically significant differences in the transfer of carbon dioxide during the bioleaching process with a transfer vector.

Sulfobacillus and Leptospirillum occur frequently in leaching systems. Here we investigated the effects of cells of L. ferriphilum on biofilm formation and leaching performance by S. thermosulfidooxidans. The effects were caused by the presence of L. ferriphilum or an addition of pyrite leach liquor from L. ferriphilum. Data show that the number of attached S. thermosulfidooxidans on pyrite increases, if the pyrite had been pre-colonized by living biofilms of L. ferriphilum, while it decreases if the pre-colonized biofilms had been inactivated. Coaggregation between S. thermosulfidooxidans and L. ferriphilum occurs during the dual-species biofilm formation, but different effects on bioleaching were noted, if the preculture of L. ferriphilum had been different. If L. ferriphilum had been pre-colonized on a pyrite, significantly negative effect was shown. However, if the two species were simultaneously inoculated into a sterile leaching system, the bioleaching efficiency was better than that of a pure culture of S. thermosulfidooxidans. The effect might be related to a metabolic preference of S. thermosulfidooxidans. If S. thermosulfidooxidans performed leaching in a filtered pyrite leachate from L. ferriphilum, the cells preferred to oxidize RISCs instead of ferrous ion and the number of attached cells decreased compared with the control. This study gives an indication that in a short-term multi-species leaching system the role of S. thermosufidooxidans may be related to the time of its introduction.

Biological methods for leaching of nonferrous and noble metals from its sulfide ores are widely applied at industrial enterprises of different countries. This process is based on the use of the oxidative activity of acidophilic microorganisms. Since all bio systems are quite sensitive to the temperature, bacterial leaching process also significantly effects. In the present study, the impact of temperature on bacterial leaching of Zn from its sulphide ore, sphalerite, was investigated using ore adapted iron oxidizing bacteria. The bacteria were isolated from mine drainage samples and subjected to gene sequencing. The acquired nucleotide sequence revealed that the isolate was Leptospirillum ferriphilum. The nucleotide sequence of L. ferriphilum isolate was submitted to National Center for Biotechnology Information (NCBI) and accession number KF743135 was assigned. Using the isolate, the Zn leaching data were collected in the 298–318 K temperature range. The results showed that leaching of Zn increases with temperature until optimum temperature of 313 K and achieves highest leaching efficiency of 96.96% within 20 days. Since bioleaching of minerals have become increasingly applied in different mining industries, there is immense important to analyze mechanistically-based kinetics for the design, optimization, operation, and control of biochemical processes. The kinetic study showed that the rate of Zn leaching was maximized at the optimum temperature. Further, the leaching data were analyzed using shrinking core model which revealed that the rate of leaching was inhibited by diffusion through product layer. Reaction kinetics is also to be contrasted with thermodynamics. Using Arrhenius law of thermodynamics, it was found that activation energy for Zn bioleaching reaction was 39.557 kJ mol−1. Such investigations will be necessitated for designing and implanting the ideal bioleaching system for metal bio-mining industries. [ABSTRACT FROM AUTHOR]

The adsorption of moderately thermophilic bacteria (A c, S.t and L f) on the surface of pyrite was studied experimentally. The bacterial adsorption on the surface of pyrite was measured at different pH values. 1. 6, 2. 0 and 2. 5) and temperatures(40 C and 45 C). Results showed that the adsorption capacity of L, f on the mineral surface is strong, when the temperature is 40 C and pH value is 2. 0, the adsorption capacity of L f reached 89. 47%. The adsorption capacity of mixed bacteria (A c : S t : L f = 1:1: 1)reached 75. 54% when pH value is 1.6. Initial temperature of solution had no significant effect on the contact angles and Zeta potentials of pyrite-grown bacteria. The contact angles and Zeta potentials decreased as the initial pH value of solution increased. The results of static microscope and scanning electron microscope showed that the bacteria were arranged in single cell or cluster on the surface of pyrite, and a large number of bacteria were adsorbed on the cracks or depressions of pyrite, which was of great significance to the leaching of minerals. [ABSTRACT FROM AUTHOR]

Sulfobacillus and Leptospirillum occur frequently in leaching systems. Here we investigated the effects of cells of L. ferriphilum on biofilm formation and leaching performance by S. thermosulfidooxidans. The effects were caused by the presence of L. ferriphilum or an addition of pyrite leach liquor from L. ferriphilum. Data show that the number of attached S. thermosulfidooxidans on pyrite increases, if the pyrite had been pre-colonized by living biofilms of L. ferriphilum , while it decreases if the pre-colonized biofilms had been inactivated. Coaggregation between S. thermosulfidooxidans and L. ferriphilum occurs during the dual-species biofilm formation, but different effects on bioleaching were noted, if the preculture of L. ferriphilum had been different. If L. ferriphilum had been pre-colonized on a pyrite, significantly negative effect was shown. However, if the two species were simultaneously inoculated into a sterile leaching system, the bioleaching efficiency was better than that of a pure culture of S. thermosulfidooxidans. The effect might be related to a metabolic preference of S. thermosulfidooxidans. If S. thermosulfidooxidans performed leaching in a filtered pyrite leachate from L. ferriphilum , the cells preferred to oxidize RISCs instead of ferrous ion and the number of attached cells decreased compared with the control. This study gives an indication that in a short-term multi-species leaching system the role of S. thermosufidooxidans may be related to the time of its introduction. [ABSTRACT FROM AUTHOR]

Forced aeration is one of the major energy consumption factors of the bioleaching process of run-of-mine ore. The effect of aeration in the microbial community has scarcely been studied at industrial level. Leptospirillum ferriphilum is one of the most representative species of the Fe3+ producing population in this kind of systems. We analyzed the effect of oxygen availability on L. ferriphilum by growth activity and transcriptional dynamics of its two terminal oxidases (cbb3 and bd complexes) under different experimental test: culture reactor, bioleaching column, and industrial heap tests. Relatively low O2 availability triggered important changes in the microbial community composition, cell growth, microbial activity and cydAB genes transcription in all cases of study. We assessed the potential role of the terminal oxidases on the adaptation to variable aeration conditions in different lifestyles of L. ferriphilum and identified transcriptional markers associated to oxygen metabolism in an industrial system. An interesting hypothesis about the possible role of the cbb3 complex in the response to oxidative stress as well as their role as a high oxygen-affinity oxidase in L. ferriphilum is proposed and discussed. This study successfully proves the function of the cydAB genes as valid genetic markers for low-grade copper industrial bioleaching systems.

The aim of this study is to investigate the potential of newly isolated strain Leptospirillum (L.) ferriphilum CC for bioleaching of pyrite and chalcopyrite in pure or mixed culture with other iron- and/or sulfur-oxidizing bacteria. In this paper, kinetics of ferrous iron (Fe2+) oxidation by newly isolated strain Leptospirillum (L.) ferriphilum CC was studied. The effect of initial Fe2+ in the concentration range of 50–400 mM on bacterial growth and iron oxidation was studied. It was shown that microbial Fe2+ oxidation was competitively inhibited by Fe3+. The influence of copper, zinc, nickel and cobalt ions on the oxidation of Fe2+ by L. ferriphilum CC was also studied. Minimal inhibitory concentrations (MIC) for each metal ion were determined. The toxicity of the ions was found to be as follows: Co > Zn > Ni > Cu. The comparison of iron oxidation kinetic parameters of L. ferriphilum CC with other strains of L. ferriphilum indicates the high potential of strain L. ferriphilum CC for biogenic regeneration of concentrated ferric iron (Fe3+) in bioleaching processes of ores and ore concentrates. Bioleaching tests indicated that the newly isolated L. ferriphilum CC can be a prospective strain for the bioleaching of sulfide minerals in pure culture or in association with other iron- and/or sulfur-oxidizing bacteria.

Forced aeration is one of the major energy consumption factors of the bioleaching process of run-of-mine ore. The effect of aeration in the microbial community has scarcely been studied at industrial level. Leptospirillum ferriphilum is one of the most representative species of the Fe3+ producing population in this kind of systems. We analyzed the effect of oxygen availability on L. ferriphilum by growth activity and transcriptional dynamics of its two terminal oxidases (cbb3 and bd complexes) under different experimental test: culture reactor, bioleaching column, and industrial heap tests. Relatively low O2 availability triggered important changes in the microbial community composition, cell growth, microbial activity and cydAB genes transcription in all cases of study. We assessed the potential role of the terminal oxidases on the adaptation to variable aeration conditions in different lifestyles of L. ferriphilum and identified transcriptional markers associated to oxygen metabolism in an industrial system. An interesting hypothesis about the possible role of the cbb3 complex in the response to oxidative stress as well as their role as a high oxygen-affinity oxidase in L. ferriphilum is proposed and discussed. This study successfully proves the function of the cydAB genes as valid genetic markers for low-grade copper industrial bioleaching systems. [ABSTRACT FROM AUTHOR]

In the paper kinetics of ferrous iron oxidation by isolated Leptospirillum ferriphilum CC was studied in conical flasks on rotary shaker. The effect of initial ferrous iron concentration on bacterial growth and substrate oxidation was studied in the concentration range of 50-400 mM FeSO4 x7H2O. The highest specific growth (0.41- 0.48 h-1) and Fe2+ oxidation rates (6.0-6.2 mM/l h) were detected at ferrous ion concentrations of 100-200 mM. At higher concentrations, the growth of bacteria and Fe2+ oxidation suppression was observed, reaching maximum values at 400 mM Fe2+. The maximum specific growth rate (μmax) of bacteria and half saturation constant (Ks) determined using Monod equation were 6.2mM /h, and 0.83h-1, respectively. It was shown that Fe2+ oxidation competitively inhibited by Fe3+ and the inhibition constant (Ki) was 61.95 mM. The comparison of kinetic parameters obtained for L. ferriphilum with other bacteria indicates the high potential of L.ferriphilum CC in leaching processes of ores and concentrates for biogenic regeneration of concentrated ferric iron. [ABSTRACT FROM AUTHOR]

• At 325 mM NaCl growth and iron oxidation of L. ferriphilum were completely inhibited. • Sb. thermosulfidooxidans tolerated higher NaCl concentrations than L. ferriphilum. • At 200 mM NaCl bioleaching of chalcopyrite by L. ferriphilum was inhibited. • Chalcopyrite leaching with Sb. thermosulfidooxidans was not inhibited by 200 mM NaCl. • Sphalerite leaching with Sb. thermosulfidooxidans was inhibited by 200 mM NaCl. In bio-hydrometallurgical operations, several studies found that besides having inhibitory effects chloride may also enhance the bacterial leaching of metal sulfides. This study compares the effect of chloride on bacterial growth, iron oxidation activity and bioleaching performance of Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans. The exposure to elevated NaCl concentrations affected cell growth and iron oxidation rate in both strains. Sb. thermosulfidooxidans showed better tolerance to NaCl than L. ferriphilum , with the concentration that inhibited biological iron oxidation and bacterial growth completely being 325 mM and 525 mM NaCl for L. ferriphilum and Sb. thermosulfidooxidans, respectively. At 100 mM NaCl, cell growth and iron oxidation of L. ferriphilum were severely slowed down while for Sb. thermosulfidooxidans , in contrast, they appeared almost unaffected. Additionally, while only 22% of L. ferriphilum cells survived after 18 h exposure to 100 mM NaCl, viability of Sb. thermosulfidooxidans was not strongly affected by 300 mM NaCl. Bioleaching of chalcopyrite and sphalerite were studied. For chalcopyrite, bioleaching by Sb. thermosulfidooxidans in the presence of 200 mM was similar to its performance in the absence of NaCl. However, bioleaching by L. ferriphilum was reduced by 50% in the presence of 200 mM NaCl. For sphalerite, bioleaching by both bacteria, L. ferriphilum and Sb. thermosulfidooxidans , was inhibited significantly in the presence of 200 mM NaCl. This study indicates that Sb. thermosulfidooxidans will be more suitable than L. ferriphilum to operate bioleaching with high chloride concentrations. Additionally, since bioleaching performance of chalcopyrite differed from bioleaching of sphalerite under similar conditions, further investigations on bioleaching with different sulfidic minerals in the presence of chloride ions are necessary. [ABSTRACT FROM AUTHOR]

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The exploration of microbial diversity in extremely acidic habitats has provided a vital base for the progression of minerals biotechnology. Three indigenous iron‐oxidizing acidophilic bacterial strains were isolated through serial dilution of enriched bacterial culture from Baiyin Copper Mine Stope, China. The morphological, biochemical, physiological, and phylogenetic characteristics of isolates were investigated. These isolates were motile, Gram‐negative, and curved shape with pleomorphism except isolate WG101 that was a straight rod. The optimum growth pH and temperature for all isolates were 1.5 and 30 °C, respectively, and showed extreme acidophilic nature. All the isolates showed obligate chemoautotrophic nature and used ferrous iron and pyrite as an energy source, however, isolates WG102 and WG103 were unable to use sulfur, while isolate WG101 could use elemental sulfur and reduced inorganic sodium thiosulfate as an energy source. The phylogenetic analyses based on 16S rRNA sequences revealed that the isolates WG101, WG102, and WG103 were homologous with Acidithiobacillus ferrooxidans strain AS2 (99%), Leptospirillum ferriphilum strain YSK (98%), and Leptospirillum ferrooxidans strain L15 (98%), respectively. These bacterial isolates showed efficient copper and zinc dissolution from the ore. The metals dissolution rate of At. ferrooxidans strain WG101 was 54.5 ± 4.33% (copper) and 49.6 ± 5% (zinc). The metals recovery rate of L. ferriphilum strain WG102 was 45.7 ± 3.5% (copper) and 40.5 ± 2.5% (zinc). The recovery rate of copper and zinc was 49.6 ± 4% and 46.5 ± 3% respectively in the case of L. ferrooxidans strain WG103. The findings of this study are consistent with the notion that the indigenous bacteria are more efficient in minerals dissolution. [ABSTRACT FROM AUTHOR]

Abstract Leptospirillum ferriphilum is the dominant iron-oxidising bacterium in traditional microbial communities utilised in bioprocesses for gold recovery from sulfidic minerals. Ferrous iron oxidation activity and growth of unadapted and thiocyanate-adapted L. ferriphilum HT was studied in batch culture across increasing thiocyanate (SCN−) concentrations in the range 0–2 mg/L to assess the feasibility of recycling remediated cyanidation wastewaters. Thiocyanate concentrations of 1 mg/L and 1.4 mg/L induced an inhibitory effect in the unadapted culture wherein ferrous iron oxidation rate and cell growth were compromised. A substantial lag in the onset of ferrous iron oxidation occurred at concentrations above 0.5 mg/L SCN−, with no oxidation activity above 1.75 mg/L SCN−. The adapted culture, however, was uninhibited across the SCN− concentration range investigated and demonstrated a higher specific ferrous iron oxidation rate owing to reduced growth. It is postulated that SCN− exposure in the absence of adaptation induces osmotic stress. Moreover, upregulation of genes associated with the synthesis of osmo-protectants may be responsible for the preservation of activity observed in the adapted culture. As L. ferriphilum is dominant within the biooxidation tank community, evidence of sustained iron oxidation activity at low-level SCN− concentrations affirms the potential of recycling bioremediated cyanidation wastewater. [ABSTRACT FROM AUTHOR]

Niche adaptation has long been recognized to drive intra-species differentiation and speciation, yet knowledge about its relatedness with hereditary variation of microbial genomes is relatively limited. Using Leptospirillum ferriphilum species as a case study, we present a detailed analysis of genomic features of five recognized strains. Genome-to-genome distance calculation preliminarily determined the roles of spatial distance and environmental heterogeneity that potentially contribute to intra-species variation within L. ferriphilum species at the genome level. Mathematical models were further constructed to extrapolate the expansion of L. ferriphilum genomes (an ‘open’ pan-genome), indicating the emergence of novel genes with new sequenced genomes. The identification of diverse mobile genetic elements (MGEs) (such as transposases, integrases, and phage-associated genes) revealed the prevalence of horizontal gene transfer events, which is an important evolutionary mechanism that provides avenues for the recruitment of novel functionalities and further for the genetic divergence of microbial genomes. Comprehensive analysis also demonstrated that the genome reduction by gene loss in a broad sense might contribute to the observed diversification. We thus inferred a plausible explanation to address this observation: the community-dependent adaptation that potentially economizes the limiting resources of the entire community. Now that the introduction of new genes is accompanied by a parallel abandonment of some other ones, our results provide snapshots on the biological fitness cost of environmental adaptation within the L. ferriphilum genomes. In short, our genome-wide analyses bridge the relation between genetic variation of L. ferriphilum with its evolutionary adaptation.

The BioGenerator is a unique microbial fuel cell for the conversion of hydrogen to electricity. It can be used in the hydrogen-based energy storage as a re-electrification device. This paper shows the results of the long-term stability testing of the BioGenerator. Using a bench scale bioreactor and electrochemical cell, it has been shown that the BioGenerator can achieve at least 3.8 years of continuous electricity generation without significant deterioration either in the biological or in the electrochemical components. The only part which was replaced twice a year was the anode in the electrochemical cell. The results of this work are a significant step towards the commercialization of the BioGenerator, especially in the energy storage sector. [ABSTRACT FROM AUTHOR]

Niche adaptation has long been recognized to drive intra-species differentiation and speciation, yet knowledge about its relatedness with hereditary variation of microbial genomes is relatively limited. Using Leptospirillum ferriphilum species as a case study, we present a detailed analysis of genomic features of five recognized strains. Genometo- genome distance calculation preliminarily determined the roles of spatial distance and environmental heterogeneity that potentially contribute to intra-species variation within L. ferriphilum species at the genome level. Mathematical models were further constructed to extrapolate the expansion of L. ferriphilum genomes (an 'open' pangenome), indicating the emergence of novel genes with new sequenced genomes. The identification of diverse mobile genetic elements (MGEs) (such as transposases, integrases, and phage-associated genes) revealed the prevalence of horizontal gene transfer events, which is an important evolutionary mechanism that provides avenues for the recruitment of novel functionalities and further for the genetic divergence of microbial genomes. Comprehensive analysis also demonstrated that the genome reduction by gene loss in a broad sense might contribute to the observed diversification. We thus inferred a plausible explanation to address this observation: the community-dependent adaptation that potentially economizes the limiting resources of the entire community. Now that the introduction of new genes is accompanied by a parallel abandonment of some other ones, our results provide snapshots on the biological fitness cost of environmental adaptation within the L. ferriphilum genomes. In short, our genomewide analyses bridge the relation between genetic variation of L. ferriphilum with its evolutionary adaptation. [ABSTRACT FROM AUTHOR]

Bioleaching experiments and electrochemical measurements were conducted to investigate the effect of pyrite on bornite bioleaching by Leptospirillum ferriphilum . Bioleaching experiments results showed that the addition of pyrite increased the redox potential to 360 mV vs. an Ag/AgCl electrode in the initial period of bioleaching process. The presence of pyrite significantly increased the copper extraction efficiency to 95.9% while the extraction value was only 19% without pyrite addition after 20 days. Furthermore, the addition of pyrite also decreased the consumption of acid during bioleaching of bornite. Especially, the total acid consumption was only 0.002 mmol at a pyrite to bornite ratio of 5:1 while the value was 2.842 mmol without pyrite addition. The results of electrochemical experiments identified that a galvanic effect existed between bornite and pyrite, and bornite was more prone to oxidation sand reduction. Tafel plot and galvanic corrosion tests indicated that the addition of pyrite accelerated the dissolution of bornite. Furthermore, the dissolution of bornite with pyrite additon was not inhibited by the formation of element sulfur and jarosite that may lead to passivation of chalcopyrite bioleaching. Based on all the observations, a mechanism model on how pyrite accelerated bornite dissolution is proposed. [ABSTRACT FROM AUTHOR]

Coal has been serving as a profuse source of energy since centuries and several attempts are being made to reduce sulphur emission levels from coal. Recently, pretreatment techniques such as ultrasonication and utilization of surfactants as additives have surfaced aiming at improving the biodesulphurization of coal. In the present study, biodesulphurization of Turkish lignite was studied for the first time using Leptospirillum ferriphilum. Attempts have been made to study the biodesulphurization aspects of the lignite sample where the effect of Fe 2+ iron, surfactant Span 80 and ultrasonication were studied under shake flask conditions. The study indicated Fe 2+ to be an essential component in the growth media for improving biodesulphurization performance (with 56.2% total sulphur removal). Span 80 (0.05% v/v) marginally enhanced the biodesulphurization of the lignite sample (nearly 61% of total sulphur removal). The carbon content in the lignite sample increased following biodesulphurization. Ultrasonication of the lignite sample, on the other hand, did not yield significant sulphur removal when compared to the effect of Span 80. About 57.6% of total sulphur could be removed from the sample when ultrasonicated for 60 min. Mineralogical characterization along with thermal analysis of the samples pre and post biodesulphurization provided more information on different phases present in coal and the effect of microbial treatment on them. [ABSTRACT FROM AUTHOR]

We evaluated uranium bioleaching from low-grade, granite-type uranium ore using mixed acidophilic microbes from uranium mine leachate. A 4854-ton plant-scale heap bioleaching process achieved sustained leaching with a uranium leaching efficiency of 88.3% using a pH of 1.0-2.0 and an Fe dosage of 3.0-5.5 g/L. Acid consumption amounted to 25.8 g HSO kg ore. Uranium bioleaching follows a diffusion-controlled kinetic model with a correlation coefficient of 0.9136. Almost all uranium was dissolved in aqueous solution, except those encapsulated in quartz particles. Therefore, heap bioleaching by mixed acidophilic microbes enables efficient, economical, large-scale recovery of uranium from low-grade ores. [ABSTRACT FROM AUTHOR]

Leptospirillum ferriphilum ( L . ferriphilum ) is a widely used microorganism in the commercial biooxidation process. Its ability to adhere to sulfide ores when grown in sulfide mineral substrates is very important for the entire biooxidation process. However, few studies have investigated the ore adhesion properties of L . ferriphilum . In this paper, the effects of temperature, pH and the passive layer of the sulfide ore surface on the ore adherence properties and biooxidation capacities of L . ferriphilum LJ02, which was screened by our laboratory, were investigated. The results of these experiments showed that both the contact and non-contact leaching mechanism were evident during the sulfide biooxidation process. L . ferriphilum LJ02 preferred the contact leaching mechanism to the non-contact leaching mechanism. Within the experimental range of temperatures from 36 °C to 46 °C, the OAR (ore adhesion ratio) of L . ferriphilum LJ02 increased initially and then decreased with the temperature. The optimum OAR was 0.84 at 41 °C. Within the experimental pH range of 1.1 to 2.0, the OAR of L . ferriphilum LJ02 decreased with pH. The optimum OAR was 0.87 at pH 1.1. It was also found that the OAR of L . ferriphilum LJ02 could be reduced by the passive layer on the surface of the sulfide ore, which was generated during the biooxidation process. Moreover, it seems that the OAR of L . ferriphilum LJ02 was proportional to the sulfide biooxidation efficiency. [ABSTRACT FROM AUTHOR]

Biomining is defined as biotechnology for metal recovery from minerals, and is promoted by the concerted effort of a consortium of acidophile prokaryotes, comprised of members of the Bacteria and Archaea domains. Ferroplasma acidiphilum and Leptospirillum ferriphilum are the dominant species in extremely acid environments and have great use in bioleaching applications; however, the role of each species in this consortia is still a subject of research. The hypothesis of this work is that F. acidiphilum uses the organic matter secreted by L. ferriphilum for growth, maintaining low levels of organic compounds in the culture medium, preventing their toxic effects on L. ferriphilum. To test this hypothesis, a characterization of Ferroplasma acidiphilum strain BRL-115 was made with the objective of determining its optimal growth conditions. Subsequently, under the optimal conditions, L. ferriphilum and F. acidiphilum were tested growing in each other's supernatant, in order to define if there was exchange of metabolites between the species. With these results, a mixed culture in batch cyclic operation was performed to obtain main specific growth rates, which were used to evaluate a mixed metabolic model previously developed by our group. It was observed that F. acidiphilum, strain BRL-115 is a chemomixotrophic organism, and its growth is maximized with yeast extract at a concentration of 0.04% wt/vol. From the experiments of L. ferriphilum growing on F. acidiphilum supernatant and vice versa, it was observed that in both cases cell growth is favorably affected by the presence of the filtered medium of the other microorganism, proving a synergistic interaction between these species. Specific growth rates were obtained in cyclic batch operation of the mixed culture and were used as input data for a Flux Balance Analysis of the mixed metabolic model, obtaining a reasonable behavior of the metabolic fluxes and the system as a whole, therefore consolidating the model previously developed. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1390-1396, 2016 [ABSTRACT FROM AUTHOR]

Leptospirillum ferriphilum Sp-Cl is a Gram negative, thermotolerant, curved, rod-shaped bacterium, isolated from an industrial bioleaching operation in northern Chile, where chalcocite is the major copper mineral and copper hydroxychloride atacamite is present in variable proportions in the ore. This strain has unique features as compared to the other members of the species, namely resistance to elevated concentrations of chloride, sulfate and metals. Basic microbiological features and genomic properties of this biotechnologically relevant strain are described in this work. The 2,475,669 bp draft genome is arranged into 74 scaffolds of 74 contigs. A total of 48 RNA genes and 2,834 protein coding genes were predicted from its annotation; 55 % of these were assigned a putative function. Release of the genome sequence of this strain will provide further understanding of the mechanisms used by acidophilic bacteria to endure high osmotic stress and high chloride levels and of the role of chloride-tolerant iron-oxidizers in industrial bioleaching operations. [ABSTRACT FROM AUTHOR]