Microbial leaching of metals from solid industrial wastes

Biotechnological applications for metal recovery have played a greater role in recovery of valuable metals from low grade sulfide minerals from the beginning of the middle era till the end of the twentieth century. With depletion of ore/minerals and implementation of stricter environmental rules, microbiological applications for metal recovery have been shifted towards solid industrial wastes. Due to certain restrictions in conventional processes, use of microbes has garnered increased attention. The process is environmentally-friendly, economical and cost-effective. The major microorganisms in recovery of heavy metals are acidophiles that thrive at acidic pH ranging from 2.0–4.0. These microbes aid in dissolving metals by secreting inorganic and organic acids into aqueous media. Some of the well-known acidophilic bacteria such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Sulfolobus spp. are well-studied for bioleaching activity, whereas, fungal species like Penicillium spp. and Aspergillus niger have been thoroughly studied for the same process. This mini-review focuses on the acidophilic microbial diversity and application of those microorganisms toward solid industrial wastes.     

Manganese biomining: A review

Biomining comprises of processing and extraction of metal from their ores and concentrates using microbial techniques. Currently this is used by the mining industry to extract copper, uranium and gold from low grade ores but not for low grade manganese ore in industrial scale. The study of microbial genomes, metabolites and regulatory pathways provide novel insights to the metabolism of bioleaching microorganisms and their synergistic action during bioleaching operations. This will promote understanding of the universal regulatory responses that the biomining microbial community uses to adapt to their changing environment leading to high metal recovery. Possibility exists of findings ways to imitate the entire process during industrial manganese biomining endeavor. This paper reviews the current status of manganese biomining research operations around the world, identifies factors that drive the selection of biomining as a processing technology, describes challenges in exploiting these innovations, and concludes with a discussion of Mn biomining’s future.     

Potential of fruit and vegetable wastes as novel biosorbents: summarizing the recent studies

Fruit and vegetable wastes produced in astronomical quantities from food processing and agriculture industries often cause nuisance in municipal landfills owing to their high biodegradability. Biosorption by these waste-based adsorbents can be used as a cost effective and efficient technique for the removal of toxic heavy metals and dyes from wastewater. Recently, many papers claiming the feasible use of these biosorbents for water decontamination, treatment of industrial and agricultural wastewater and valuable metal recovery have been published. The organic waste-based adsorbents, characterized by good uptake capacity and rapid kinetics are expected to be economically and ecologically viable. This paper presents a judicious and pragmatic review depicting the key advances in implications of the fruit and vegetable wastes in pollution mitigation, the underlying mechanisms, major challenges and the future implementations. This compilation is expected to provide an impetus to the bioremediation research and promote green technology.     

Microorganisms resistant to heavy metals and toxic chemicals as indicators of environmental pollution and their use in bioremediation

Microorganisms present in water samples from various industrial effluents were analysed for their resistance to lead, chromium, and cadmium. The ability of these microorganisms to grow on or metabolize toxic hydrocarbons and pesticides was also checked. Microorganisms in samples from the steel and tanning industries were generally resistant to metal ions but were not capable of metabolizing toxic hydrocarbons. Conversely, microorganisms found in samples of pesticide and from the chemical industry were capable of metabolizing hydrocarbons and pesticides but were not much resistant to metal ions. Microorganisms from effluents of the paint industry and urban wastes were resistant to lead. A correlation between the population of microorganisms and the type of pollution was observed. Indigenous microorganism could be regarded as indicators of pollution and be used in various operations to resist, process, metabolize, and detoxify toxic industrial wastes.     

Enzyme Production of the Edible Mushroom Pleorotus ostreatus in Shaken Cultures Completed with Agro‐Industrial Wastes

The enzyme production of the white‐rot fungus, the edible mushroom Pleurotus ostreatus, was determined in shaken culture media containing extracts of agro‐industrial wastes (tomato, potato and pepper residues) as an unique carbon source. The activity of β‐glucosidase, xylanase, laccase as well as manganese‐dependent and independent peroxidases was measured at 0, 3.5, 7.0, 10.5, 14.0, 17.5, 21.0, 24.5, 28.0 and 31.5 days of cultivation. A spectral mapping technique and non‐linear mapping were employed for the calculation of the relationships among the fermentation parameters, such as fermentation time, enzyme activity and selectivity of enzyme production. It was established that P. ostreatus produced β‐glucosidase, xylanase, laccase, manganese‐dependent and independent peroxidases in each culture medium and that the enzyme activities were higher in cultures containing agro‐industrial wastes than in the control containing glucose as a carbon source. The spectral mapping technique allowed demonstrating that the enzyme activities were the highest in the culture completed with pepper extract followed by cultures containing potato and tomato extracts. The differences among the selectivity of the enzyme activities were negligible up to 21.0 days of fermentation and reached the maximum at the end of the fermentation process. The production of laccase as well as manganese‐dependent and independent peroxidases showed similar patterns while the selectivity patterns of xylanase and β‐galactoside production were different. In addition, it became evident that the agro‐industrial wastes influenced the enzyme production in a distinct way.     

Metal cation controls phosphate release in the myosin ATPase

Myosin is an enzyme that utilizes ATP to produce a conformational change generating a force. The kinetics of the myosin reverse recovery stroke depends on the metal cation complexed with ATP. The reverse recovery stroke is slow for MgATP and fast for MnATP. The metal ion coordinates the γ phosphate of ATP in the myosin active site. It is accepted that the reverse recovery stroke is correlated with the phosphate release; therefore, magnesium “holds” phosphate tighter than manganese. Magnesium and manganese are similar ions in terms of their chemical properties and the shell complexation; hence, we propose to use these ions to study the mechanism of the phosphate release. Analysis of octahedral complexes of magnesium and manganese show that the partial charge of magnesium is higher than that of manganese and the slightly larger size of manganese ion makes its ionic potential smaller. We hypothesize that electrostatics play a role in keeping and releasing the abstracted γ phosphate in the active site, and the stronger electric charge of magnesium ion holds γ phosphate tighter. We used stable myosin–nucleotide analog complex and Raman spectroscopy to examine the effect of the metal cation on the relative position of γ phosphate analog in the active site. We found that in the manganese complex, the γ phosphate analog is 0.01 nm further away from ADP than in the magnesium complex. We conclude that the ionic potential of the metal cation plays a role in the retention of the abstracted phosphate.     

Cleanup of industrial effluents containing heavy metals: a new opportunity of valorising the biomass produced by brewing industry

Heavy metal pollution is a matter of concern in industrialised countries. Contrary to organic pollutants, heavy metals are not metabolically degraded. This fact has two main consequences: its bioremediation requires another strategy and heavy metals can be indefinitely recycled. Yeast cells of Saccharomyces cerevisiae are produced at high amounts as a by-product of brewing industry constituting a cheap raw material. In the present work, the possibility of valorising this type of biomass in the bioremediation of real industrial effluents containing heavy metals is reviewed. Given the auto-aggregation capacity (flocculation) of brewing yeast cells, a fast and off-cost yeast separation is achieved after the treatment of metal-laden effluent, which reduces the costs associated with the process. This is a critical issue when we are looking for an effective, eco-friendly, and low-cost technology. The possibility of the bioremediation of industrial effluents linked with the selective recovery of metals, in a strategy of simultaneous minimisation of environmental hazard of industrial wastes with financial benefits from reselling or recycling the metals, is discussed.     

Novel polymerase chain reaction primers for the specific detection of bacterial copper P‐type ATPases gene sequences in environmental isolates and metagenomic DNA

Aims: In the last decades, the worldwide increase in copper wastes release by industrial activities like mining has driven environmental metal contents to toxic levels. For this reason, the study of the biological copper‐resistance mechanisms in natural environments is important. Therefore, an appropriate molecular tool for the detection and tracking of copper‐resistance genes was developed. Methods and Results: In this work, we designed a PCR primer pair to specifically detect copper P‐type ATPases gene sequences. These PCR primers were tested in bacterial isolates and metagenomic DNA from intertidal marine environments impacted by copper pollution. As well, T‐RFLP fingerprinting of these gene sequences was used to compare the genetic composition of such genes in microbial communities, in normal and copper‐polluted coastal environments. New copper P‐type ATPases gene sequences were found, and a high degree of change in the genetic composition because of copper exposure was also determined. Conclusions: This PCR based method is useful to track bacterial copper‐resistance gene sequences in the environment. Significance and Impact of the Study: This study is the first to report the design and use of a PCR primer pair as a molecular marker to track bacterial copper‐resistance determinants, providing an excellent tool for long‐term analysis of environmental communities exposed to metal pollution.     

Inhibition of anaerobic digestion process: a review

Anaerobic digestion is an attractive waste treatment practice in which both pollution control and energy recovery can be achieved. Many agricultural and industrial wastes are ideal candidates for anaerobic digestion because they contain high levels of easily biodegradable materials. Problems such as low methane yield and process instability are often encountered in anaerobic digestion, preventing this technique from being widely applied. A wide variety of inhibitory substances are the primary cause of anaerobic digester upset or failure since they are present in substantial concentrations in wastes. Considerable research efforts have been made to identify the mechanism and the controlling factors of inhibition. This review provides a detailed summary of the research conducted on the inhibition of anaerobic processes. The inhibitors commonly present in anaerobic digesters include ammonia, sulfide, light metal ions, heavy metals, and organics. Due to the difference in anaerobic inocula, waste composition, and experimental methods and conditions, literature results on inhibition caused by specific toxicants vary widely. Co-digestion with other waste, adaptation of microorganisms to inhibitory substances, and incorporation of methods to remove or counteract toxicants before anaerobic digestion can significantly improve the waste treatment efficiency.     

典型固体废物中冶金微生物及其浸出机理研究进展

典型固体废物(废电器、废电池、污泥、焚烧飞灰、废催化剂等)含有大量金属资源，回收再利用的价值极高。微生物浸出典型固体废物受多因素影响。对不同微生物浸出金属的菌种筛选、浸出规律和机理的掌握，有助于典型固体废物中金属资源的绿色高效回收，可为我国“双碳”目标作出贡献。本文综述了从典型固体废物中浸出金属的各类微生物，分析了冶金微生物的作用机制，并展望了微生物冶金的应用前景，以期为微生物冶金技术在典型固体废物中的高效应用提供理论参考。     

Recent advances in microbial mining

Microbial mining of copper sulphide ores, has been practiced on an industrial scale since the late 1950s. Since then, advances in microbial mining and the role of microorganisms involved in solubilization of metals have assumed commerical importance. The fact that bioleaching processes save energy, have a minimum pollution potential and are able to yield value-added by-products make these processes invaluable. The metal extraction processes using microorganisms, which are currently in active use, concern copper and uranium bioleaching. Biobeneficiation is also applied at an industrial scale for recovery of gold from arsenopyrites. The developments in these processes during the last 15 years, with particular reference to developing nations, are reviewed. Information gathered on molecular genetics of these microorganisms should lead to a better understanding and control of microbial leaching processes. Areas still needing research to sustain economic expansion of microbial mining techniques are indicated.The author is with the Agharkar Research Institute, Agarkar Road, Pune 411 004, India     

Diverse molecular resistance mechanisms of <Emphasis Type="Italic">Bacillus megaterium</Emphasis> during metal removal present in a spent catalyst

Bacillus megaterium strain MNSH1-9K-1, isolated from a high-metal content site in Guanajuato, Mexico, has the intrinsic capacity to remove vanadium (V) and nickel (Ni) from a petrochemical spent catalyst, and counteract the toxic effects produced in the cell due to the presence of oxidative stress. Since knowledge of the molecular components involved in the microbial resistance to spent catalysts is scarce, this study aimed to identify the proteins potentially involved in the enhanced resistance of a B. megaterium strain, during the removal of metals contained in a spent catalyst. Thus, the current research uses a proteomic approach to investigate and evidence the differences in the molecular resistance mechanisms of two B. megaterium strains, one isolated from a mining site and a wild type strain, when both are exposed to a spent catalyst. In addition, we studied their ability to eliminate nickel (Ni), vanadium (V), aluminum (Al) and molybdenum (Mo). The data presented here may contribute to the knowledge of the molecular mechanisms involved in the resistance of B. megaterium to high metal content wastes, as well as its potential utilization for the recovery of valuable industrial metals.     

Soil Manganese Enrichment from Industrial Inputs: A Gastropod Perspective

Manganese is one of the most abundant metal in natural environments and serves as an essential microelement for all living systems. However, the enrichment of soil with manganese resulting from industrial inputs may threaten terrestrial ecosystems. Several studies have demonstrated harmful effects of manganese exposure by cutaneous contact and/or by soil ingestion to a wide range of soil invertebrates. The link between soil manganese and land snails has never been made although these invertebrates routinely come in contact with the upper soil horizons through cutaneous contact, egg-laying, and feeding activities in soil. Therefore, we have investigated the direct transfer of manganese from soils to snails and assessed its toxicity at background concentrations in the soil. Juvenile Cantareus aspersus snails were caged under semi-field conditions and exposed first, for a period of 30 days, to a series of soil manganese concentrations, and then, for a second period of 30 days, to soils with higher manganese concentrations. Manganese levels were measured in the snail hepatopancreas, foot, and shell. The snail survival and shell growth were used to assess the lethal and sublethal effects of manganese exposure. The transfer of manganese from soil to snails occurred independently of food ingestion, but had no consistent effect on either the snail survival or shell growth. The hepatopancreas was the best biomarker of manganese exposure, whereas the shell did not serve as a long-term sink for this metal. The kinetics of manganese retention in the hepatopancreas of snails previously exposed to manganese-spiked soils was significantly influenced by a new exposure event. The results of this study reveal the importance of land snails for manganese cycling in terrestrial biotopes and suggest that the direct transfer from soils to snails should be considered when precisely assessing the impact of anthropogenic Mn releases on soil ecosystems.     

Long-term changes in heavy metal loadings of Ascophyllum nodosum from the Firth of Clyde,UK

The aim of this work is to describe changes in heavy metal concentrations in Ascophyllum nodosum from 1964 to 1994. Samples were collected from three sites in the Firth of Clyde and analysed for zinc, manganese, iron, copper, lead and nickel. The results were analysed using the multivariate technique Principal Components Analysis (PCA). At the Wemyss Bay site there was a trend towards increasing lead and nickel over the study period, which could not be accounted for by local industrial activity. At the Hunterston site, two groups were well separated by the PCA ordination, based on manganese and zinc concentrations, which corresponded to land reclamation activities in the area. The separation of samples at the Ardneil Bay site correlated well with copper concentration and this corresponded to the termination of industrial effluent with heavy copper loadings. Other changes in industrial effluent were also reflected in the Hunterston and Ardneil Bay site ordinations. The PCA technique highlighted the interplay between metals. The work demonstrated the potential for using multivariate analysis of seaweed metal concentrations in monitoring a posteriori the environmental impact of industrial change.     

A method for large scale purification of turnip peroxidase and its characterization

Purification of peroxidase has been carried out since 1960 from different sources and with different methods. Ion exchange, affinity, hydrophobic, and metal affinity chromatography are known, to our knowledge. The present method, developed in this study, is three-phase partitioning, a novel technique to separate protein directly from a large volume of crude suspension. It has been observed that interfacing phase with a metal makes this technique highly selective. Turnip peroxidase purified with this method has 512 units/mg with 20.3% recovery. The natural proteins containing histidine or cystine are often purified by immobilized metal affinity chromatography. The purification of turnip peroxidase with the three-phase partitioning technique is based on immobilized metal affinity chromatography and is used for large-scale purification. The present method, described here, would prove its value in purifying an industrially important enzyme on a large scale from a crude suspension. The enzyme purified with this technique showed two bands on SDS- PAGE, which showed a molecular weight of approx. 39KD. Enzyme showed maximum purification with Cu++ metal and had a maximum activity at pH 6.0. The enzyme has an affinity towards hydrogen peroxide as its substrate in the presence of orthodianisidine as a chromogenic substrate. Enzyme activity was enhanced with calcium and magnesium, whereas sodium, potassium, and manganese inhibit the enzyme activity.     

Molecular design of the microbial cell surface toward the recovery of metal ions

The genetic engineering of microorganisms to adsorb metal ions is an attractive method to facilitate the environmental cleanup of metal pollution and to enrich the recovery of metal ions such as rare metal ions. For the recovery of metal ions by microorganisms, cell surface design is an effective strategy for the molecular breeding of bioadsorbents as an alternative to intracellular accumulation. The cell surface display of known metal-binding proteins/peptides and the molecular design of novel metal-binding proteins/peptides have been performed using a cell surface engineering approach. The adsorption of specific metal ions is the important challenge for the practical recovery of metal ions. In this paper, we discuss the recent progress in surface-engineered bioadsorbents for the recovery of metal ions.     

Field bioassays for early detection of chronic impacts of chemical wastes upon marine organisms

A major problem facing those who must assess the environmental effects of the disposal in the ocean of industrial and municipal wastes, including dredged materials, is determining whether given wastes elicit chronic deteriorative responses in important species of organisms. The full importance of such low-level, nonlethal effects is not known, but it is suspected that repeated elicitations may result in ecosystem changes as important as those caused by more easily determinable acute effects. Such considerations are important to the marine environment, where dumped pollutants may be quickly diluted to legal nonlethal concentrations, but may still bring forth cumulative chronic response patterns. One objective of this study has been to develop a field method of assessing the impacts of the disposal of various industrial and municipal wastes. The measure of the impact is not mortality measured against time, but the increase or decrease in activity of certain metabolic enzymes that signal whether an organism is under stress from a class of wastes. Also, by analysing tissues of test and indigenous species for the accumulation of metals, PCBs, and high molecular weight hydrocarbons as well as for the enzyme activity, one gains an insight into the actual effect, if any, of the accumulation upon the whole organism. The test organisms are exposed for selected periods of time in the field in devices called Biotal Ocean Monitors (BOMs); they are then assayed for enzyme induction. At present the following enzymes are used: mitochondrial ATPase, which responds particularly to excess biphenyls in the environment; catalase that is dissolved in the cytosol and responds to excesses of toxic metals; and cytochrome P-420 and P-450, which respond to cyclic and long-chain hydrocarbons. The applicability of the adenylate energy charge system to this problem is also studied.     

X-ray structure of the cambialistic superoxide dismutase from Propionibacterium shermanii active with Fe or Mn

The first structure of a cambialistic superoxide dismutase (SOD) from Propionibacterium shermanii exhibiting similar activity with iron and with manganese was solved at a resolution of 1.6?Å and 1.9?Å respectively. Surprisingly, no obvious differences between the two SODs were observable. The protein crystallises as a homo dimer in the asymmetric unit. Because of the crystallographic symmetry, it forms a tetramer. Structures of both the manganese and the ferric form were solved using molecular replacement techniques and multiple isomorphous replacement. The tertiary structure is similar to that of the other superoxide dismutases, the metal being fivefold coordinated by three histidines, one aspartate and one water molecule. The second shell of residues consists of hydrophobic amino acids, histidines and two water molecules, which are assumed to be involved in both the catalytic activity and structural stability of this superoxide dismutase. This shell may also be responsible for the cambialistic behaviour. This work shows that the reason for the metal specificity is not trivial, although minor alterations in the metal environment might be responsible for this behaviour.