Molybdate reduction to molybdenum blue by an Antarctic bacterium

Molybdenum tolerance of strains screened from molybdenum tailings and their potential application in molybdenum-contaminated soils

Mining and smelting activities of molybdenum (Mo) have led to increasingly severe Mo pollution in the environment, posing potential threats to ecosystems and human health. Microbial remediation technology has emerged as an effective approach for reducing Mo pollution due to its environmental friendliness and cost-effectiveness. In this study, two Mo (Ⅵ) tolerant strains (MoTB 2 and MoTB 79) with exceptional Mo reduction capacities were isolated and identified from the rhizosphere soil of pioneer plants in Mo-contaminated tailings. Systematic studies were conducted to evaluate their Mo tolerance, reduction efficiency, and underlying mechanisms in both controlled and soil environments. The results showed that both strains exhibited robust growth in high-Mo (VI) conditions (6000 mg L-1), comparable to Mo-free environments, with optimal growth observed at pH 5.0 and 30°C. Notably, under conditions of 5.0 mmol L-1 phosphate and 60.0 mmol L-1 molybdate, the strains demonstrated significant Mo (Ⅵ) removal capabilities (14.8%-22.5% within 24 h) via bioconversion to molybdate. Further mechanistic analysis using a multi-technique approach revealed that FTIR spectroscopy identified phosphate groups, amide bonds, C-O-C, and -CH groups as key functional entities for extracellular Mo (Ⅵ) adsorption, while TEM-EDX confirmed intracellular bioaccumulation. Critically, XPS quantification demonstrated valence state transformations, with 79.8%-86.3% of toxic Mo (Ⅵ) reduced to less toxic Mo (Ⅳ) (23.4%-39.7%) and Mo (Ⅴ) (40.1%-63.0%). To bridge laboratory findings with environmental applications, soil remediation experiments revealed an 11.8%-19.6% conversion of mobile Mo (Ⅵ) to immobilized Mo (0) and Mo (Ⅳ) fractions via XANES, effectively passivating bioavailable Mo. Notably, the strains also exhibited phosphate/potassium solubilization capabilities, suggesting dual roles in metal detoxification and nutrient cycling. This integrated study elucidates the potential of MoTB strains as eco-engineers for bioremediation in Mo-contaminated ecosystems through adsorption, bioaccumulation, multi-valence reduction, and soil fertility enhancement.

Effects of heavy metals on bacterial growth parameters in degradation of phenol by an Antarctic bacterial consortium

Antarctica has often been perceived as a pristine continent until the recent few decades as pollutants have been observed accruing in the Antarctic environment. Irresponsible human activities such as accidental oil spills, waste incineration and sewage disposal are among the primary anthropogenic sources of heavy metal contaminants in Antarctica. Natural sources including animal excrement, volcanism and geological weathering also contribute to the increase of heavy metals in the ecosystem. A microbial growth model is presented for the growth of a bacterial cell consortium used in the biodegradation of phenol in media containing different metal ions, namely arsenic (As), cadmium (Cd), aluminium (Al), nickel (Ni), silver (Ag), lead (Pb) and cobalt (Co). Bacterial growth was inhibited by these ions in the rank order of Al < As < Co < Pb < Ni < Cd < Ag. Greatest bacterial growth occurred in 1 ppm Al achieving an OD600 of 0.985 and lowest in 1 ppm Ag with an OD600 of 0.090. At a concentration of 1.0 ppm, Ag had a considerable effect on the bacterial consortium, inhibiting the degradation of phenol, whereas this concentration of the other metal ions tested had no effect on degradation. The biokinetic growth model developed supports the suitability of the bacterial consortium for use in phenol degradation.

Potential applications of extremophilic bacteria in the bioremediation of extreme environments contaminated with heavy metals

Protecting the environment from harmful pollutants has become increasingly difficult in recent decades. The presence of heavy metal (HM) pollution poses a serious environmental hazard that requires intricate attention on a worldwide scale. Even at low concentrations, HMs have the potential to induce deleterious health effects in both humans and other living organisms. Therefore, various strategies have been proposed to address this issue, with extremophiles being a promising solution. Bacteria that exhibit resistance to metals are preferred for applications involving metal removal due to their capacity for rapid multiplication and growth. Extremophiles are a special group of microorganisms that are capable of surviving under extreme conditions such as extreme temperatures, pH levels, and high salt concentrations where other organisms cannot. Due to their unique enzymes and adaptive capabilities, extremophiles are well suited as catalysts for environmental biotechnology applications, including the bioremediation of HMs through various strategies. The mechanisms of resistance to HMs by extremophilic bacteria encompass: (i) metal exclusion by permeability barrier; (ii) extracellular metal sequestration by protein/chelator binding; (iii) intracellular sequestration of the metal by protein/chelator binding; (iv) enzymatic detoxification of a metal to a less toxic form; (v) active transport of HMs; (vi) passive tolerance; (vii) reduced metal sensitivity of cellular targets to metal ions; and (viii) morphological change of cells. This review provides comprehensive information on extremophilic bacteria and their potential roles for bioremediation, particularly in environments contaminated with HMs, which pose a threat due to their stability and persistence. Genetic engineering of extremophilic bacteria in stressed environments could help in the bioremediation of contaminated sites. Due to their unique characteristics, these organisms and their enzymes are expected to bridge the gap between biological and chemical industrial processes. However, the structure and biochemical properties of extremophilic bacteria, along with any possible long-term effects of their applications, need to be investigated further.

Antarctic heavy metal pollution and remediation efforts: state of the art of research and scientific publications

In Antarctica, human activities have been reported to be the major cause of the accumulation of heavy metal contaminants. A comprehensive bibliometric analysis of publications on heavy metal contamination in Antarctica from year 2000 to 2020 was performed to obtain an overview of the current landscape in this line of research. A total of 106 documents were obtained from Scopus, the largest citation database. Extracted data were analysed, and VOSviewer software was used to visualise trends. The result showed an increase in publications and citations in the past 20 years indicating the rising interest on heavy metal contamination in the Antarctic region. Based on the analysis of keywords, the publications largely discuss various types of heavy metals found in the Antarctic water and sediment. The analysis on subject areas detects multiple disciplines involved, wherein the environmental science was well-represented. The top countries and authors producing the most publication in this field were from Australia, China, Brazil and Chile. Numerous efforts have been exercised to investigate heavy metal pollution and its mitigation approaches in the region in the past decades. This paper not only is relevant for scholars to understand the development status and trends in this field but also offers clear insights on the future direction of Antarctic heavy metal contamination and remediation research.

The potential of Pseudomonas for bioremediation of oxyanions

Non-metal, metal and metalloid oxyanions occur naturally in minerals and rocks of the Earth's crust and are mostly found in low concentrations or confined in specific regions of the planet. However, anthropogenic activities including urban development, mining, agriculture, industrial activities and new technologies have increased the release of oxyanions to the environment, which threatens the sustainability of natural ecosystems, in turn affecting human development. For these reasons, the implementation of new methods that could allow not only the remediation of oxyanion contaminants but also the recovery of valuable elements from oxyanions of the environment is imperative. From this perspective, the use of microorganisms emerges as a strategy complementary to physical, mechanical and chemical methods. In this review, we discuss the opportunities that the Pseudomonas genus offers for the bioremediation of oxyanions, which is derived from its specialized central metabolism and the high number of oxidoreductases present in the genomes of these bacteria. Finally, we review the current knowledge on the transport and metabolism of specific oxyanions in Pseudomonas species. We consider that the Pseudomonas genus is an excellent starting point for the development of biotechnological approaches for the upcycling of oxyanions into added-value metal and metalloid byproducts.

Optimisation of Various Physicochemical Variables Affecting Molybdenum Bioremediation Using Antarctic Bacterium, Arthrobacter sp. Strain AQ5-05

The versatility of a rare metal, molybdenum (Mo) in many industrial applications is one of the reasons why Mo is currently one of the growing environmental pollutants worldwide. Traces of inorganic contaminants, including Mo, have been discovered in Antarctica and are compromising the ecosystem. Bioremediation utilising bacteria to transform pollutants into a less toxic form is one of the approaches for solving Mo pollution. Mo reduction is a process of transforming sodium molybdate with an oxidation state of 6+ to Mo-blue, an inert version of the compound. Although there are a few Mo-reducing microbes that have been identified worldwide, only two studies were reported on the microbial reduction of Mo in Antarctica. Therefore, this study was done to assess the ability of Antarctic bacterium, Arthrobacter sp. strain AQ5-05, in reducing Mo. Optimisation of Mo reduction in Mo-supplemented media was carried out using one-factor-at-a-time (OFAT) and response surface methodology (RSM) approaches. Through OFAT, Mo was reduced optimally with substrate concentration of sucrose, ammonium sulphate, and molybdate at 1 g/L, 0.2 g/L, and 10 mM, respectively. The pH and salinity of the media were the best at 7.0 and 0.5 g/L, respectively, while the optimal temperature was at 10 °C. Further optimisation using RSM showed greater Mo-blue production in comparison to OFAT. The strain was able to stand high concentration of Mo and low temperature conditions, thus showing its potential in reducing Mo in Antarctica by employing conditions optimised by RSM.

Statistical Optimisation and Kinetic Studies of Molybdenum Reduction Using a Psychrotolerant Marine Bacteria Isolated from Antarctica

The extensive industrial use of the heavy metal molybdenum (Mo) has led to an emerging global pollution with its traces that can even be found in Antarctica. In response, a reduction process that transforms hexamolybdate (Mo6+) to a less toxic compound, Mo-blue, using microorganisms provides a sustainable remediation approach. The aim of this study was to investigate the reduction of Mo by a psychrotolerant Antarctic marine bacterium, Marinomonas sp. strain AQ5-A9. Mo reduction was optimised using One-Factor-At-a-Time (OFAT) and Response Surface Methodology (RSM). Subsequently, Mo reduction kinetics were further studied. OFAT results showed that maximum Mo reduction occurred in culture media conditions of pH 6.0 and 50 ppt salinity at 15 °C, with initial sucrose, nitrogen and molybdate concentrations of 2.0%, 3.0 g/L and 10 mM, respectively. Further optimization using RSM identified improved optimum conditions of pH 6.0 and 47 ppt salinity at 16 °C, with initial sucrose, nitrogen and molybdate concentrations of 1.8%, 2.25 g/L and 16 mM, respectively. Investigation of the kinetics of Mo reduction revealed Aiba as the best-fitting model. The calculated Aiba coefficient of maximum Mo reduction rate (µmax) was 0.067 h−1. The data obtained support the potential use of marine bacteria in the bioremediation of Mo.

Microbiological Reduction of Molybdenum to Molybdenum Blue as a Sustainable Remediation Tool for Molybdenum: A Comprehensive Review

Molybdenum (Mo) microbial bioreduction is a phenomenon that is beginning to be recognized globally as a tool for the remediation of molybdenum toxicity. Molybdenum toxicity continues to be demonstrated in many animal models of spermatogenesis and oogenesis, particularly those of ruminants. The phenomenon has been reported for more than 100 years without a clear understanding of the reduction mechanism, indicating a clear gap in the scientific knowledge. This knowledge is not just fundamentally important-it is specifically important in applications for bioremediation measures and the sustainable recovery of metal from industrial or mine effluent. To date, about 52 molybdenum-reducing bacteria have been isolated globally. An increasing number of reports have also been published regarding the assimilation of other xenobiotics. This phenomenon is likely to be observed in current and future events in which the remediation of xenobiotics requires microorganisms capable of degrading or transforming multi-xenobiotics. This review aimed to comprehensively catalogue all of the characterizations of molybdenum-reducing microorganisms to date and identify future opportunities and improvements.

INTERACTION OF OBLIGATE ANAEROBIC DESTROYER OF SOLID ORGANIC WASTE Clostridium butyricum GMP1 WITH SOLUBLE COMPOUNDS OF TOXIC METALS Cr(VI), Mo(VI) AND W(VI)

Increasing pollution of environment by toxic metals is the urgent problem requiring effective solution worldwide. The goal of the work was to study the dynamics of the interaction of Cr(VI), Mo(VI), W(VI) compounds with obligate anaerobic microorganisms Clostridium butyricum GMP1, which ferment organic compounds with the synthesis of hydrogen. The standard methods were used to determine рН and redox potential (Eh), the gas composition, and the concentration of metals. The application Clostridium butyricum GMP1 was showed to be useful to investigate its interaction with toxic metals. The higher redox potential of metal provided the opportunity for its faster and more effective reduction. The patterns of the reduction of toxic metals Cr(VI), Mo(VI) and W(VI) by obligate anaerobic strain Clostridium butyricum GMP1 were obtained. The experimental data confirmed the thermodynamically calculated correlation between the redox potential of the metal reduction to insoluble form and effectiveness of its removal. Obtained results can serve as the basis for further optimization and development of environmental biotechnologies for wastewater treatment with the simultaneous destruction of solid organic waste and hydrogen synthesis.

Characterisation of the simultaneous molybdenum reduction and glyphosate degradation by Burkholderia vietnamiensis AQ5-12 and Burkholderia sp. AQ5-13

In this novel study, we report on the use of two molybdenum-reducing bacteria with the ability to utilise the herbicide glyphosate as the phosphorus source. The bacteria reduced sodium molybdate to molybdenum blue (Mo-blue), a colloidal and insoluble product, which is less toxic. The characterisation of the molybdenum-reducing bacteria was carried out using resting cells immersed in low-phosphate molybdenum media. Two glyphosate-degrading bacteria, namely Burkholderia vietnamiensis AQ5-12 and Burkholderia sp. AQ5-13, were able to use glyphosate as a phosphorous source to support molybdenum reduction to Mo-blue. The bacteria optimally reduced molybdenum between the pHs of 6.25 and 8. The optimum concentrations of molybdate for strain Burkholderia vietnamiensis strain AQ5-12 was observed to be between 40 and 60 mM, while for Burkholderia sp. AQ5-13, the optimum molybdate concentration occurred between 40 and 50 mM. Furthermore, 5 mM of phosphate was seen as the optimum concentration supporting molybdenum reduction for both bacteria. The optimum temperature aiding Mo-blue formation ranged from 30 to 40 °C for Burkholderia vietnamiensis strain AQ5-12, whereas for Burkholderia sp. AQ5-13, the range was from 35 to 40 °C. Glucose was the best electron donor for supporting molybdate reduction, followed by sucrose, fructose and galactose for both strains. Ammonium sulphate was the best nitrogen source in supporting molybdenum reduction. Interestingly, increasing the glyphosate concentrations beyond 100 and 300 ppm for Burkholderia vietnamiensis strain AQ5-12 and Burkholderia sp. AQ5-13, respectively, significantly inhibited molybdenum reduction. The ability of these bacteria to reduce molybdenum while degrading glyphosate is a useful process for the bioremediation of both toxicants.

Optimisation of culture composition for glyphosate degradation by Burkholderia vietnamiensis strain AQ5-12

The herbicide glyphosate is often used to control weeds in agricultural lands. However, despite its ability to effectively kill weeds at low cost, health problems are still reported due to its toxicity level. The removal of glyphosate from the environment is usually done by microbiological process since chemical process of degradation is ineffective due to the presence of highly stable bonds. Therefore, finding glyphosate-degrading microorganisms in the soil of interest is crucial to remediate this glyphosate. Burkholderia vietnamiensis strain AQ5-12 was found to have glyphosate-degrading ability. Optimisation of biodegradation condition was carried out utilising one factor at a time (OFAT) and response surface methodology (RSM). Five parameters including carbon and nitrogen source, pH, temperature and glyphosate concentration were optimised. Based on OFAT result, glyphosate degradation was observed to be optimum at fructose concentration of 6, 0.5 g/L ammonia sulphate, pH 6.5, temperature of 32 °C and glyphosate concentration at 100 ppm. Meanwhile, RSM resulted in a better degradation with 92.32% of 100 ppm glyphosate compared to OFAT. The bacterium was seen to tolerate up to 500 ppm glyphosate while increasing concentration results in reduced degradation and bacterial growth rate.

Determination of element composition and extraterrestrial material occurrence in moss and lichen samples from King George Island (Antarctica) using reactor neutron activation analysis and SEM microscopy

Seven lichens (Usnea antarctica and U. aurantiacoatra) and nine moss samples (Sanionia uncinata) collected in King George Island were analyzed using instrumental neutron activation analysis, and concentration of major and trace elements was calculated. For some elements, the concentrations observed in moss samples were higher than corresponding values reported from other sites in the Antarctica, but in the lichens, these were in the same range of concentrations. Scanning electron microscopy (SEM) and statistical analysis showed large influence of volcanic-origin particles. Also, the interplanetary cosmic particles (ICP) were observed in investigated samples, as mosses and lichens are good collectors of ICP and micrometeorites.

Impacts of residual aluminum from aluminate flocculant on the morphological and physiological characteristics of Vallisneria natans and Hydrilla verticillata

Aluminate is generally used as a flocculant in water and wastewater treatment processes, but the residual aluminum (Al) may have toxic effects on aquatic organisms when the concentration accumulates beyond a threshold level. The in situ and laboratory tests were conducted to evaluate the impact of residual Al on submerged macrophytes in West Lake, Hangzhou, China, which receives Al flocculant-purified water diverted from the Qiantang River. The responses of Vallisneria natans and Hydrilla verticillata were investigated based on their morphological and physiological parameters in pot culture and aquarium simulation experiments. In the pot culture experiments, the biomass, seedling number, plant height, stolon number, stolon length, and root weight were significantly higher at a site located 150m from the inlet compared with those at a site located 15m from the inlet (P < 0.05), thereby indicating that the residual Al significantly inhibited the morphological development of V. natans and H. verticillata. The variations in the chlorophyll-a, protein, and malondialdehyde contents of the two species in both the pot culture and aquarium simulation experiments also demonstrated that the two submerged macrophytes were stressed by residual Al. V. natans and H. verticillata accumulated 0.052-0.227mg of Al per gram of plant biomass (fresh weight, mg/g FW) and 0.045-0.205mg Al/g FW in the in situ experiments, respectively, where the amounts of Al were significantly higher in the plants in the treatment aquaria during the laboratory experiments than those in the controls. These results may have important implications for the restoration of submerged macrophytes and ecological risk assessments in Al-exposed lakes. It is recommended that the Al salt concentration used for the control of lake eutrophication should be reduced to an appropriate level.

Isolation and Characterisation of a Molybdenum-reducing and Metanil Yellow Dye-decolourising Bacillus sp. strain Neni-10 in Soils from West Sumatera, Indonesia

A molybdenum reducing bacterium with the novel ability to decolorise the azo dye Metanil Yellow is reported. Optimal conditions for molybdenum reduction were pH 6.3 and at 34°C. Glucose was the best electron donor. Another requirement includes a narrow phosphate concentration between 2.5 and 7.5 mM. A time profile of Mo-blue production shows a lag period of approximately 12 hours, a maximum amount of Mo-blue produced at a molybdate concentration of 20 mM, and a peak production at 52 h of incubation. The heavy metals mercury, silver, copper and chromium inhibited reduction by 91.9, 82.7, 45.5 and 17.4%, respectively. A complete decolourisation of the dye Metanil Yellow at 100 and 150 mg/L occurred at day three and day six of incubations, respectively. Higher concentrations show partial degradation, with an approximately 20% decolourisation observed at 400 mg/L. The bacterium is partially identified based on biochemical analysis as Bacillus sp. strain Neni-10. The absorption spectrum of the Mo-blue suggested the compound is a reduced phosphomolybdate. The isolation of this bacterium, which shows heavy metal reduction and dye-decolorising ability, is sought after, particularly for bioremediation.

Complete genome sequence of the molybdenum-resistant bacterium Bacillus subtilis strain LM 4-2

Bacillus subtilis LM 4–2, a Gram-positive bacterium was isolated from a molybdenum mine in Luoyang city. Due to its strong resistance to molybdate and potential utilization in bioremediation of molybdate-polluted area, we describe the features of this organism, as well as its complete genome sequence and annotation. The genome was composed of a circular 4,069,266 bp chromosome with average GC content of 43.83 %, which included 4149 predicted ORFs and 116 RNA genes. Additionally, 687 transporter-coding and 116 redox protein-coding genes were identified in the strain LM 4–2 genome.

Phylogenetic relationship of phosphate solubilizing bacteria according to 16S rRNA genes

Phosphate solubilizing bacteria (PSB) can convert insoluble form of phosphorous to an available form. Applications of PSB as inoculants increase the phosphorus uptake by plant in the field. In this study, isolation and precise identification of PSB were carried out in Malaysian (Serdang) oil palm field (University Putra Malaysia). Identification and phylogenetic analysis of 8 better isolates were carried out by 16S rRNA gene sequencing in which as a result five isolates belong to the Beta subdivision of Proteobacteria, one isolate was related to the Gama subdivision of Proteobacteria, and two isolates were related to the Firmicutes. Bacterial isolates of 6upmr, 2upmr, 19upmnr, 10upmr, and 24upmr were identified as Alcaligenes faecalis. Also, bacterial isolates of 20upmnr and 17upmnr were identified as Bacillus cereus and Vagococcus carniphilus, respectively, and bacterial isolates of 31upmr were identified as Serratia plymuthica. Molecular identification and characterization of oil palm strains as the specific phosphate solubilizer can reduce the time and cost of producing effective inoculate (biofertilizer) in an oil palm field.