Multiple metal tolerance and biosorption of cadmium by Candida tropicalis isolated from industrial effluents: glutathione as detoxifying agent

Unlocking Cd(II) biosorption potential of Candida tropicalis XTA 1874 for sustainable wastewater treatment

Cd(II) is a potentially toxic heavy metal having carcinogenic activity. It is becoming widespread in the soil and groundwater by various natural and anthropological activities. This is inviting its immediate removal. The present study is aimed at developing a Cd(II) resistant strain isolated from contaminated water body and testing its potency in biological remediation of Cd(II) from aqueous environment. The developed resistant strain was characterized by SEM, FESEM, TEM, EDAX, FT-IR, Raman Spectral, XRD and XPS analysis. The results depict considerable morphological changes had taken place on the cell surface and interaction of Cd(II) with the surface exposed functional groups along with intracellular accumulation. Molecular contribution of critical cell wall component has been evaluated. The developed resistant strain had undergone Cd(II) biosorption study by employing adsorption isotherms and kinetic modeling. Langmuir model best fitted the Cd(II) biosorption data compared to the Freundlich one. Cd(II) biosorption by the strain followed a pseudo second order kinetics. The physical parameters affecting biosorption were also optimized by employing response surface methodology using central composite design. The results depict remarkable removal capacity 75.682 ± 0.002% of Cd(II) by the developed resistant strain from contaminated aqueous medium using 500 ppm of Cd(II). Quantitatively, biosorption for Cd(II) by the newly developed resistant strain has been increased significantly (p < 0.0001) from 4.36 ppm (non-resistant strain) to 378.41 ppm (resistant strain). It has also shown quite effective desorption capacity 87.527 ± 0.023% at the first desorption cycle and can be reused effectively as a successful Cd(II) desorbent up to five cycles. The results suggest that the strain has considerable withstanding capacity of Cd(II) stress and can be employed effectively in the Cd(II) bioremediation from wastewater.

The Cd resistant mechanism of Proteus mirabilis Ch8 through immobilizing and detoxifying

Cadmium (Cd) pollution is a serious global environmental problem, which requires a global concern and practical solutions. Microbial remediation has received widespread attention owing to advantages, such as environmental friendliness and soil amelioration. However, Cd toxicity also severely deteriorates the remediation performance of functional microorganisms. Analyzing the mechanism of bacterial resistance to Cd stress will be beneficial for the application of Cd remediation. In this study, the bacteria strain, up to 1400 mg/L Cd resistance, was employed and identified as Proteus mirabilis Ch8 (Ch8) through whole genome sequence analyses. The results indicated that the multiple pathways of immobilizing and detoxifying Cd maintained the growth of Ch8 under Cd stress, which also possessed high Cd extracellular adsorption. Firstly, the changes in surface morphology and functional groups of Ch8 cells were observed under different Cd conditions through SEM-EDS and FTIR analyses. Under 100 mg/L Cd, Ch8 cells exhibited aggregation and less flagella; the Cd biosorption of Ch8 was predominately by secreting exopolysaccharides (EPS) and no significant change of functional groups. Under 500 mg/L Cd, Ch8 were present irregular polymers on the cell surface, some cells with wrapping around; the Cd biosorption capacity exhibited outstanding effects (38.80 mg/g), which was mainly immobilizing Cd by secreting and interacting with EPS. Then, Ch8 also significantly enhanced the antioxidant enzyme activity and the antioxidant substance content under different Cd conditions. The activities of SOD and CAT, GSH content of Ch8 under 500 mg/L Cd were significantly increased by 245.47%, 179.52%, and 241.81%, compared to normal condition. Additionally, Ch8 significantly induced the expression of Acr A and Tol C (the resistance-nodulation-division (RND) efflux pump), and some antioxidant genes (SodB, SodC, and Tpx) to reduce Cd damage. In particular, the markedly higher expression levels of SodB under Cd stress. The mechanism of Ch8 lays a foundation for its application in solving soil remediation.

Characterization of heavy metal-associated bacteria from petroleum-contaminated soil and their resistogram and antibiogram analysis

The aim of the current study was to screen and identify heavy metal (chromium, cadmium, and lead) associated bacteria from petroleum-contaminated soil of district Muzaffarabad, Azad Jammu and Kashmir, Pakistan to develop ecofriendly technology for contaminated soil remediation. The petroleum-contaminated soil was collected from 99 different localities of district Muzaffarabad and the detection of heavy metals via an atomic absorption spectrometer. The isolation and identification of heavy metals-associated bacteria were done via traditional and molecular methods. Resistogram and antibiogram analysis were also performed using agar well diffusion and agar disc diffusion methods. The isolated bacteria were classified into species, i.e., B. paramycoides, B. albus, B. thuringiensis, B. velezensis, B. anthracis, B. pacificus Burkholderia arboris, Burkholderia reimsis, Burkholderia aenigmatica, and Streptococcus agalactiae. All heavy metals-associated bacteria showed resistance against both high and low concentrations of chromium while sensitive towards high and low concentrations of lead in the range of 3.0 ± 0.0 mm to 13.0 ± 0.0 mm and maximum inhibition was recorded when cadmium was used. Results revealed that some bacteria showed sensitivity towards Sulphonamides, Norfloxacin, Erythromycin, and Tobramycin. It was concluded that chromium-resistant bacteria could be used as a favorable source for chromium remediation from contaminated areas and could be used as a potential microbial filter.

Plants-Microorganisms-Based Bioremediation for Heavy Metal Cleanup: Recent Developments, Phytoremediation Techniques, Regulation Mechanisms, and Molecular Responses

Rapid industrialization, mine tailings runoff, and agricultural activities are often detrimental to soil health and can distribute hazardous metal(loid)s into the soil environment, with harmful effects on human and ecosystem health. Plants and their associated microbes can be deployed to clean up and prevent environmental pollution. This green technology has emerged as one of the most attractive and acceptable practices for using natural processes to break down organic contaminants or accumulate and stabilize metal pollutants by acting as filters or traps. This review explores the interactions between plants, their associated microbiomes, and the environment, and discusses how they shape the assembly of plant-associated microbial communities and modulate metal(loid)s remediation. Here, we also overview microbe-heavy-metal(loid)s interactions and discuss microbial bioremediation and plants with advanced phytoremediation properties approaches that have been successfully used, as well as their associated biological processes. We conclude by providing insights into the underlying remediation strategies' mechanisms, key challenges, and future directions for the remediation of metal(loid)s-polluted agricultural soils with environmentally friendly techniques.

Heavy metal-induced oxidative stress and alteration in secretory proteins in yeast isolates

In the recent years, yeasts have evolved as potent bioremediative candidates for the detoxification of xenobiotic compounds found in the natural environment. Candida sp. are well-studied apart from Saccharomyces sp. in heavy metal detoxification mechanisms. In the current study, Candida parapsilosis strain ODBG2, Candida sp. strain BANG3, and Candida viswanathii strain ODBG4 were isolated from industrial effluents and contaminated ground water, and were studied for their metal tolerance. Among these three isolates, the metal tolerance was found to be more towards Lead (Pb 2 mM), followed by Cadmium (Cd 1.5 mM) and Chromium [Cr(VI), 1 mM]. On further exploring the involvement of primary defensive enzymes in these isolates towards metal tolerance, the anti-oxidative enzyme superoxide dismutase was found to be prominently high (25% with respect to the control) during first 24 h of metal-isolate interaction. The Catalase enzyme assay was observed to have increased enzyme activity at 48 h. It also triggered the activity of peroxidases, which lead to the increase in reduced glutathione in the organism by 0.87-1.9-fold as a metal chelator and also as a second-line defensive molecule. The exoproteome profile showed the early involvement (exponential growth phase) of secreted proteins (low-molecular-weight) of about ~ 40-45 kDa under Cd and Pb stress (0.5 mM). The exoproteome profiling under heavy metal stress in Candida parapsilosis strain ODBG2 and Candida viswanathii strain ODBG4 is the first report.

Determination of Fungal Tolerance Index to Heavy Metals and Heavy Metal Resistance Tests

Fungal metallo-tolerance has been described in different species and plays an important role in bioremediation of contaminated environments. Metallo-tolerance is mainly documented by microdilution assays and agar well diffusion methods using equipment that can be expensive. The tolerance index can be calculated to determine the efficiency of a fungus to degrade and resist heavy metals. The present protocol is based on analyzing the tolerance index and minimum inhibitory concentration of the metallo-tolerance potential of culturable fungi on solid media. This can be calculated by daily measurements of colony size on agar supplemented with different concentrations of heavy metals. This method is an easy approach to determine fungal heavy metal resistance using simple laboratory equipment without spectroscopy.

Antimicrobial coatings for environmental surfaces in hospitals: a potential new pillar for prevention strategies in hygiene

Recent reports provide evidence that contaminated healthcare environments represent major sources for the acquisition and transmission of pathogens. Antimicrobial coatings (AMC) may permanently and autonomously reduce the contamination of such environmental surfaces complementing standard hygiene procedures. This review provides an overview of the current status of AMC and the demands to enable a rational application of AMC in health care settings. Firstly, a suitable laboratory test norm is required that adequately quantifies the efficacy of AMC. In particular, the frequently used wet testing (e.g. ISO 22196) must be replaced by testing under realistic, dry surface conditions. Secondly, field studies should be mandatory to provide evidence for antimicrobial efficacy under real-life conditions. The antimicrobial efficacy should be correlated to the rate of nosocomial transmission at least. Thirdly, the respective AMC technology should not add additional bacterial resistance development induced by the biocidal agents and co- or cross-resistance with antibiotic substances. Lastly, the biocidal substances used in AMC should be safe for humans and the environment. These measures should help to achieve a broader acceptance for AMC in healthcare settings and beyond. Technologies like the photodynamic approach already fulfil most of these AMC requirements.

Microbial retention and resistances in stormwater quality improvement devices treating road runoff

Current knowledge about the microbial communities that occur in urban road runoff is scarce. Road runoff of trafficked roads can be heavily polluted and is treated by stormwater quality improvement devices (SQIDs). However, microbes may influence the treatment process of these devices or could lead to stress resistant opportunistic microbial strains. In this study, the microbial community in the influent, effluent and the filter materials used to remove dissolved heavy metals from two different SQIDs were analyzed to determine microbial load, retention, composition, and mobile resistance genes. Although the microbes were replaced by new taxa in the effluent, there was no major retention of microbial genera. Further, the bacterial abundance of the SQIDs effluent was relatively stable over time. The heavy metal content correlated with intl1 and with microbial genera. The filter media itself was enriched with Intl1 gene cassettes, carrying several heavy metal and multidrug resistance genes (e.g. czrA, czcA, silP, mexW and mexI), indicating that this is a hot spot for horizontal gene transfer. Overall, the results shed light on road runoff microbial communities, and pointed to distinct bacterial communities within the SQIDs, which subsequently influence the microbial community and the genes released with the treated water.

Bioremediation potential and lead removal capacity of heavy metal-tolerant yeasts isolated from Dayet Oum Ghellaz Lake water (northwest of Algeria)

Seven metal-resistant yeast strains were isolated and selected from Dayet Oum Ghellaz Lake water (northwest of Algeria) known as a highly polluted area by lead and cadmium. The yeast strains were screened on the basis of their resistance to seven heavy metals Hg, Cr, Cd, Pb, Cu, Zn, and Fe and characterized by molecular and phylogenetic analysis. The sequencing of the D1/D2 domain of the 26S rRNA genes revealed the affiliation of the seven yeast isolates to Rhodotorula mucilaginosa, Clavispora lusitaniae, and Wickerhamomyces anomalus species. All yeast strains were halotolerant as they were able to grow in 10-15% NaCl. The yeast isolates were highly resistant to the studied heavy metals and exhibited different tolerance according to the metal type. The highest minimum inhibitory concentrations (MIC) were observed in R. mucilaginosa RO7 and W. anomalus WO2 strains which were then selected for lead removal assays. The present study is the first to investigate the lead elimination by W. anomalus. The lead uptake was significantly affected by biomass concentration in a reverse relationship, with purification percentages estimated at 98.15 ± 0.9% and 97.046 ± 0.47% and removal efficiency of 12.68 ± 0.91 and 15.55 ± 0.72 mg/g for W. anomalus WO2 and R. mucilaginosa RO7, respectively. The investigated metal-tolerant yeast strains proved to be promising candidates for bioremediation processes of heavy metals. This work amends the metal-resistant yeast bank with new strains having interesting abilities to resist to relatively high concentrations of toxic heavy metals and which can be used in the near future as low-cost biosorbents.

Phylogeny, evolution, and potential ecological relationship of cytochrome CYP52 enzymes in Saccharomycetales yeasts

Cytochrome P450s from the CYP52 family participate in the assimilation of alkanes and fatty acids in fungi. In this work, the evolutionary history of a set of orthologous and paralogous CYP52 proteins from Saccharomycetales yeasts was inferred. Further, the phenotypic assimilation profiles were related with the distribution of cytochrome CYP52 members among species. The maximum likelihood phylogeny of CYP52 inferred proteins reveled a frequent ancient and modern duplication and loss events that generated orthologous and paralogous groups. Phylogeny and assimilation profiles of alkanes and fatty acids showed a family expansion in yeast isolated from hydrophobic-rich environments. Docking analysis of deduced ancient CYP52 proteins suggests that the most ancient function was the oxidation of C4-C11 alkanes, while the oxidation of >10 carbon alkanes and fatty acids is a derived character. The ancient CYP52 paralogs displayed partial specialization and promiscuous interaction with hydrophobic substrates. Additionally, functional optimization was not evident. Changes in the interaction of ancient CYP52 with different alkanes and fatty acids could be associated with modifications in spatial orientations of the amino acid residues that comprise the active site. The extended family of CYP52 proteins is likely evolving toward functional specialization, and certain redundancy for substrates is being maintained.

Yeast strain Debaryomyces hansenii for amelioration of arsenic stress in rice

Arsenic (As) is a serious threat for environment and human health. Rice, the main staple crop is more prone to As uptake. Bioremediation strategies with heavy metal tolerant rhizobacteria are well known. The main objective of the study was to characterize arsenic-resistant yeast strains, capable of mitigating arsenic stress in rice. Three yeast strains identified as Debaryomyces hansenii (NBRI-Sh2.11), Candida tropicalis (NBRI-B3.4) and Candida dubliniensis (NBRI-3.5) were found to have As reductase activity. D. hansenii with higher As tolerance has As expulsion ability as compared to other two strains. Inoculation of D. hansenii showed improved detoxification through scavenging of reactive oxygen species (ROS) by the modulation of SOD and APX activity under As stress condition in rice. Modulation of defense responsive gene (NADPH, GST, GR) along with arsR and metal cation transporter are the probable mechanism of As detoxification as evident with improved membrane (electrolyte leakage) stability. Reduced grain As (~40% reduction) due to interaction with D. hansenii (NBRI-Sh2.11) further validated it's As mitigation property in rice. To the best of our knowledge D. hansenii has been reported for the first time for arsenic stress mitigation in rice with improved growth and nutrient status of the plant.

Alleviating the toxicity of quantum dots to Phanerochaete chrysosporium by sodium hydrosulfide and cysteine

Quantum dots (QDs) have caused large challenges in clinical tests and biomedical applications due to their potential toxicity from nanosize effects and heavy metal components. In this study, the physiological responses of Phanerochaete chrysosporium (P. chrysosporium) to CdSe/ZnS QDs with either an inorganic sulfide NaHS or an organic sulfide cysteine as antidote have been investigated. Scanning electron microscope analysis showed that the hyphal structure and morphology of P. chrysosporium have obviously changed after exposure to 100 nM of COOH CdSe/ZnS 505, NH₂ CdSe/ZnS 505, NH₂ CdSe/ZnS 565, or NH₂ CdSe/ZnS 625. Fourier transform infrared spectroscopy analysis indicated that the existence of hydroxyl, amino, and carboxyl groups on cell surface could possibly conduct the stabilization of QDs in an aqueous medium. However, after NaHS or cysteine treatment, the cell viability of P. chrysosporium exposed to CdSe/ZnS QDs increased as compared to control group, since NaHS and cysteine have assisted P. chrysosporium to alleviate oxidative damage by regulating lipid peroxidation and superoxide production. Meanwhile, NaHS and cysteine have also stimulated P. chrysosporium to produce more antioxidant enzymes (superoxide dismutase and catalase), which played significant roles in the defense system. In addition, NaHS and cysteine were used by P. chrysosporium as sulfide sources to promote the glutathione biosynthesis to relieve CdSe/ZnS QDs-induced oxidative stress. This work revealed that sulfide sources (NaHS and cysteine) exerted a strong positive effect in P. chrysosporium against the toxicity induced by CdSe/ZnS QDs.

Bacterial Heavy-Metal and Antibiotic Resistance Genes in a Copper Tailing Dam Area in Northern China

Heavy metal resistance genes (MRGs) and antibiotic resistance genes (ARGs) in bacteria can respond to the inducement of heavy metals. However, the co-occurrence of MRGs and ARGs in the long-term heavy metal contaminated area is still poorly understood. Here, we investigated the relationship between the abundance of soil bacteria MRGs, ARGs and heavy metal pollution in a copper tailing dam area of northern China. We found that arsC and ereA genes coding for resistance mechanisms to arsenic and to macrolides, respectively, are the most abundant MRG and ARG in the study area. The abundance of MRGs is positively correlated with cadmium (Cd) concentration, and this indicates the importance of Cd in the selection of MRGs. The network analysis results show that sulII and MRGs co-occur and copB occur with ARGs, which suggests that MRGs and ARGs can be co-selected in the soil contaminated by heavy metal. The network analysis also reveals the co-occurrence of Cd and MRGs, and thus heavy metal with a high 'toxic-response' factor can be used as the indicator of MRGs. This study improves the understanding of the relationship between bacterial resistance and multi-metal contamination, and underlies the exploration of the adaptive mechanism of microbes in the multi-metal contaminated environment.

Cadmium induces GAPDH- and- MDH mediated delayed cell aging and dysfunction in Candida tropicalis 3Aer

Eukaryotes employ various mechanisms to survive environmental stress conditions. Multicellular organisms eliminate permanently damaged cells by apoptosis, while unicellular eukaryotes like yeast react by decelerating cell aging. In the present study, transcriptomic and proteomic approaches were employed to elucidate the underlying mechanism of delayed apoptosis. Our findings suggest that Candida tropicalis 3Aer has a set of tightly controlled genes that are activated under Cd⁺² exposition. Acute exposure to Cd⁺² halts the cell cycle at the G₂/M phase checkpoint and activates multiple cytoplasmic proteins that overcome effects of Cd⁺²-induced reactive oxygen species. Prolonged Cd⁺² stress damages DNA and initiates GAPDH amyloid formation. This is the first report that Cd⁺² challenge initiates dynamic redistribution of GAPDH and MDH and alters various metabolic pathways including the pentose phosphate pathway. In conclusion, the intracellular redistribution of GAPDH and MDH induced by prolonged cadmium stress modulates various cellular reactions, which facilitate delayed aging in the yeast cell.

Bioremoval of Cobalt(II) from Aqueous Solution by Three Different and Resistant Fungal Biomasses

The biosorption of Co(II) on three fungal biomasses: Paecilomyces sp., Penicillium sp., and Aspergillus niger, was studied in this work. The fungal biomass of Paecilomyces sp. showed the best results, since it removes 93% at 24 h of incubation, while the biomasses of Penicillium sp. and Aspergillus niger are less efficient, since they remove the metal 77.5% and 70%, respectively, in the same time of incubation, with an optimum pH of removal for the three analyzed biomasses of 5.0 ± 0.2 at 28°C. Regarding the temperature of incubation, the most efficient biomass was that of Paecilomyces sp., since it removes 100%, at 50°C, while the biomasses of Penicillium sp. and Aspergillus niger remove 97.1% and 94.1%, at the same temperature, in 24 hours of incubation. On the contrary, if the concentration of the metal is increased, the removal capacity for the three analyzed biomasses decreases; if the concentration of the bioadsorbent is increased, the removal of the metal also increases. It was observed that, after 4 and 7 days of incubation, 100%, 100%, and 96.4% of Co(II) present in naturally contaminated water were removed, respectively.

Bioremoval of Different Heavy Metals by the Resistant Fungal Strain Aspergillus niger

The objective of this work was to study the resistance and removal capacity of heavy metals by the fungus Aspergillus niger. We analyzed the resistance to some heavy metals by dry weight and plate: the fungus grew in 2000 ppm of zinc, lead, and mercury, 1200 and 1000 ppm of arsenic (III) and (VI), 800 ppm of fluor and cobalt, and least in cadmium (400 ppm). With respect to their potential of removal of heavy metals, this removal was achieved for zinc (100%), mercury (83.2%), fluor (83%), cobalt (71.4%), fairly silver (48%), and copper (37%). The ideal conditions for the removal of 100 mg/L of the heavy metals were 28°C, pH between 4.0 and 5.5, 100 ppm of heavy metal, and 1 g of fungal biomass.

Lead-induced oxidative stress and antioxidant response provide insight into the tolerance of Phanerochaete chrysosporium to lead exposure

The present work investigated the effect of lead (Pb) on the growth, metal accumulation, oxidative stress, and antioxidant response in Phanerochaete chrysosporium, which is a well-known hyperaccumulating species for heavy metal with appreciable bioaccumulation capacity. Results revealed that P. chrysosporium exhibited a good ability in Pb accumulation and tolerance over a concentration range of 50-100 mg L^-1 Pb. The removal rate of Pb decreased with the increasing levels of Pb and reached a maximum of 91.3% at 50 mg L^-1. Both extracellular adsorption and intracellular bioaccumulation contributed to the removal of Pb, with the maximum of 123.8 mg g^-1 and 162.5 mg g^-1 dry weight, respectively. Pb may exert its toxicity to P. chrysosporium by impairing oxidative metabolism, as evidenced by the enhanced accumulation of hydrogen peroxide (H₂O₂) and lipid peroxidation product malonaldehyde (MDA). P. chrysosporium evolved an antioxidant system by elevating the activity of superoxide dismutase (SOD) and the level of reduced glutathione (GSH) in response to Pb stress, whereas decreasing the activities of catalase (CAT) and peroxidase (POD). Moreover, Pearson correlation analysis demonstrated a good correlation between oxidative stress biomarkers and enzymatic antioxidants. The preset work suggested that P. chrysosporium exhibited an outstanding accumulation of Pb and tolerance of Pb-induced oxidative stress by the effective antioxidant defense mechanism.

Molecular basis of Cd+2 stress response in Candida tropicalis

This study examines the bioremediation potential and cadmium-induced cellular response on a molecular level in Candida tropicalis 3Aer. Spectroscopic analysis clearly illustrated the involvement of yeast cell wall components in biosorption. Cadmium bioaccumulation was confirmed by TEM, SEM, and EDX examination. TEM images revealed extracellular as well as cytoplasmic and vacuolar cadmium nanoparticle formation, further validated by presence of ycf1 gene and increased biosynthesis of GSH under cadmium stress. Fourteen proteins exhibited differential expression and during cellular redox homeostasis are found to involve in nitrogen metabolism, nucleotide biosynthesis, and carbohydrate catabolism. Interestingly, C. tropicalis 3Aer is equipped with nitrile hydratase enzyme, rarely been reported in yeast. It has the potential to remove nitriles from the environment. The Cd⁺² toxicity not only caused growth stasis but also upregulated the cysteine biosynthesis, protein folding and cytoplasmic detoxification response elements. The present study suggests that C. tropicalis 3Aer is a potential candidate for bioremediating environmental pollution by Cd⁺².

Biosorption Performance of Encapsulated Candida krusei for the removal of Copper(II)

The use of microorganisms in biosorption is one of the most promising ways to remove trace amounts of heavy metal ions. Nevertheless, the enhancement of the successful removal of heavy metal ions by using different combinations of biosorbents is not generally guaranteed which leaves room to explore the application of the technique. In this study, the performance of free and immobilized forms of a yeast strain, Candida krusei (C. krusei), and calcium alginate (CaAlg) are evaluated for their ability to remove copper(II). Infrared spectroscopy, studies on the effects of pH and temperature, and kinetics and isotherm modelling are carried out to evaluate the biosorption. The infrared spectroscopy shows that the primary biosorption sites on the biosorbents are carboxylate groups. In addition, a higher pH and higher temperatures promote biosorption while a decline in biosorption ability is observed for C. krusei at 50 °C. The kinetics study shows that C. krusei, CaAlg and immobilized C. krusei (MCaAlg) conform with good correlation to pseudo-second order kinetics. MCaAlg and CaAlg fit well to the Langmuir isotherm while C. krusei fits well to the Temkin isotherm. From the experimental data, encapsulating C. krusei showed improved biosoprtion and address clogging in practical applications.

Resistance and uptake of cadmium by yeast, Pichia hampshirensis 4Aer, isolated from industrial effluent and its potential use in decontamination of wastewater

Pichia hampshirensis 4Aer is first ever used yeast for the bioremediation of environmental cadmium (Cd(+2)) which could maximally remove 22 mM/g and 28 mM/g Cd(+2) from aqueous medium at lab and large scales, respectively. The biosorption was found to be the function of temperature, pH of solution, initial Cd(+2) concentration and biomass dosage. Competitive biosorption was investigated in binary and multi-metal system which indicated the decrease in Cd(+2) biosorption with increasing the competitive metal ions attributed to their higher electronegativity and larger radius. FTIR analysis revealed the active participation of amide and carbonyl moieties in Cd(+2) adsorption confirmed by EDX analysis. Electron micrographs summoned further surface adsorption and increased cell size due to intracellular Cd(+2) accumulation. Cd(+2) was the causative agent of some metal binding proteins as well as prodigious increase in glutathione and other non-protein thiols levels which is the crucial for the yeast to thrive oxidative stress generated by Cd(+2). Our experimental data were consistent with Langmuir as well as Freundlich isotherm models. The yeast obeyed pseudo second order kinetic model which makes it an effective biosorbent for Cd(+2). High bioremediation potential and spontaneity and feasibility of the process make P. hampshirensis 4Aer an impending foundation for green chemistry to exterminate environmental Cd(+2).

Arsenic processing of yeast isolates IIB-As1 & IIB-As2 and production of glutathione under stress conditions

Four arsenic resistant yeast were isolated from the industrial wastewater. Two strains IIB-As1 and IIB-As2 identified as Candida tropicalis and Saccharomyces cerevisiae, respectively. IIB-As1 and IIB-As2 showed maximum arsenic resistance. IIB-As1 showed maximum growth at 35 °C whereas it was 30 °C for IIB-As2. The yeast isolate showed typical growth curves, but arsenic extended the lag phase. Glutathione plays an important role in metal tolerance. In the present study, As increased the level glutathione and non-protein thiols in yeast isolates. Removal of As from supernatant was analyzed using the atomic absorption spectrophotometer. They removed arsenic from the medium after 72 h of incubation. Both yeast strains efficiently removed arsenic from the industrial effluent when used individually or in consortia.

Effects of nitrogen sources and metal ions on ethanol fermentation with cadmium-containing medium

This study evaluated ethanol fermentation and its correlation with glutathione (GSH) synthesis under various cadmium-conditions with different metal ions and nitrogen sources. We found that corn steep liquor (CSL) and yeast extract have differential roles to play in GSH accumulation in cell even though both of them could alleviate the inhibition by cadmium. The different GSH accumulation in cell resulted from the different contents of metal ions in CSL and yeast extract. Intracellular GSH decreased with increasing calcium concentrations, and high calcium concentrations rendered the yeast more tolerant to cadmium stress than the nitrogen sources did. When the mole ratio of calcium to cadmium was 100:1, yeast tolerated 1000 µmol/L cadmium with no decrease in efficiency in ethanol production. As a result, the use of calcium allowed a significant saving of high-cost nutrient yeast extract with an efficient ethanol production, making the bioconversion of cadmium-containing biomass into ethanol possible.

Antioxidant enzymes activities of Burkholderia spp. strains-oxidative responses to Ni toxicity

Increased agriculture production associated with intense application of herbicides, pesticides, and fungicides leads to soil contamination worldwide. Nickel (Ni), due to its high mobility in soils and groundwater, constitutes one of the greatest problems in terms of environmental pollution. Metals, including Ni, in high concentrations are toxic to cells by imposing a condition of oxidative stress due to the induction of reactive oxygen species (ROS), which damage lipids, proteins, and DNA. This study aimed to characterize the Ni antioxidant response of two tolerant Burkholderia strains (one isolated from noncontaminated soil, SNMS32, and the other from contaminated soil, SCMS54), by measuring superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione S-transferase (GST) activities. Ni accumulation and bacterial growth in the presence of the metal were also analyzed. The results showed that both strains exhibited different trends of Ni accumulation and distinct antioxidant enzymes responses. The strain from contaminated soil (SCMS54) exhibited a higher Ni biosorption and exhibited an increase in SOD and GST activities after 5 and 12 h of Ni exposure. The analysis of SOD, CAT, and GR by nondenaturing PAGE revealed the appearance of an extra isoenzyme in strain SCMS54 for each enzyme. The results suggest that the strain SCMS54 isolated from contaminated soil present more plasticity with potential to be used in soil and water bioremediation.

Genes related to antioxidant metabolism are involved in Methylobacterium mesophilicum-soybean interaction

The genus Methylobacterium is composed of pink-pigmented methylotrophic bacterial species that are widespread in natural environments, such as soils, stream water and plants. When in association with plants, this genus colonizes the host plant epiphytically and/or endophytically. This association is known to promote plant growth, induce plant systemic resistance and inhibit plant infection by phytopathogens. In the present study, we focused on evaluating the colonization of soybean seedling-roots by Methylobacterium mesophilicum strain SR1.6/6. We focused on the identification of the key genes involved in the initial step of soybean colonization by methylotrophic bacteria, which includes the plant exudate recognition and adaptation by planktonic bacteria. Visualization by scanning electron microscopy revealed that M. mesophilicum SR1.6/6 colonizes soybean roots surface effectively at 48 h after inoculation, suggesting a mechanism for root recognition and adaptation before this period. The colonization proceeds by the development of a mature biofilm on roots at 96 h after inoculation. Transcriptomic analysis of the planktonic bacteria (with plant) revealed the expression of several genes involved in membrane transport, thus confirming an initial metabolic activation of bacterial responses when in the presence of plant root exudates. Moreover, antioxidant genes were mostly expressed during the interaction with the plant exudates. Further evaluation of stress- and methylotrophic-related genes expression by qPCR showed that glutathione peroxidase and glutathione synthetase genes were up-regulated during the Methylobacterium-soybean interaction. These findings support that glutathione (GSH) is potentially a key molecule involved in cellular detoxification during plant root colonization. In addition to methylotrophic metabolism, antioxidant genes, mainly glutathione-related genes, play a key role during soybean exudate recognition and adaptation, the first step in bacterial colonization.

The influence of the earthworm Lampito mauritii (Kinberg) on the activity of selected soil enzymes in cadmium-amended soil

The effects of cadmium (CdCl2·7H2O) on cellulase, urease, amylase, invertase and phosphatase were assessed for a period of 45 days in the presence and absence of earthworms [Lampito mauritii (Kinberg)] in alfisol soil. The activities of all enzymes significantly increased with longer incubation times (45 days) under laboratory conditions in both control and Cd-amended soils (both with and without earthworm incubation). However, the activities of all enzymes decreased with increasing Cd concentrations under laboratory conditions, both in the presence and absence of earthworms. In the presence of earthworms, cellulase, urease, invertase and amylase activities increased. However, phosphatase activity was lower in most of the Cd-amended soils in the presence of earthworms compared to its activity levels in soils lacking earthworms. These results show that earthworms modulated the stress imposed by Cd by providing suitable substrates, which in turn acted as stimulants for extracellular enzyme secretion by microbes, and by removing Cd through its accumulation in the tissues of the earthworms.

Tolerance and antioxidant response of a dark septate endophyte (DSE), Exophiala pisciphila, to cadmium stress

The growth, oxidative damage and antioxidant response of Exophiala pisciphila ACCC32496, a dark septate endophyte isolated from an abandoned lead-zinc mining area, were measured at cadmium (Cd) concentrations of 0, 25, 50, 100, 200 and 400 mg L(-1). The EC50 values of E. pisciphila ACCC32496 to Cd were 332.2 mg L(-1) after 30 days on solid medium and 111.2 mg L(-1) after 7 days in liquid medium. Cd stress markedly stimulated the production of superoxide anion, H2O2 and malondialdehyde in the fungal mycelia. The activities of superoxide dismutase and catalase reached their maxima at 100 mg L(-1) Cd. The glutathione and non-protein thiol contents, along with the total antioxidant capability, reached their maxima at 50 mg L(-1) Cd. Low Cd concentrations induced a noticeable increase in antioxidant defense, while high Cd concentrations decreased the antioxidant defense.

Oxidative stress, glutathione level and antioxidant response to heavy metals in multi-resistant pathogen, Candida tropicalis

In this study, we explored the multiple heavy metal-resistant yeast isolated from heavy metal-polluted environment. The isolated yeast showed maximum growth at 30 °C, pH 7.0, and the strain was identified as Candida tropicalis through 18S ribosomal RNA (rRNA) gene sequence analysis. Yeast cells grew well in medium containing different concentrations of heavy metal ions [CdCl₂, Pb(NO₃)₂, NaAsO₂, CuSO₄ and K₂Cr₂O₇]. Minimum inhibitory concentration (MIC) against different metal ions was ranged from 5 to 19 mM, and the metal resistance value against each metal observed by yeast cells was 5 mM (Cr), 10 mM (Cd), 15 mM (As), 14 mM (Cu) and 19 mM (Pb) and increased in the following order: Pb > Cu > As ≥ Cd > Cr. The total cellular glutathione, GSH/GSSG redox couple and metallothioneins like protein (MT) were assayed by growing cultures for 24 h and exposed to 100 mg/L of each heavy metal ion. Remarkable increase in γ-glutamylcysteinylglycine (GSH) level was determined in arsenic and cadmium treatment followed by chromium, lead and copper. Stressed cells had much more oxidized GSH than unstressed cells. GSH/GSSG ratio was significantly increased in cadmium and copper treatment in contrast to chromium, arsenic and lead. Statistical analysis revealed significantly higher cysteine level in all metal-treated samples as compared to control. Antioxidant glutathione transferase activity was not detected in metal-treated and untreated yeast samples. One-dimensional electrophoresis of proteins revealed marked differences in banding pattern of heavy metal-exposed yeast samples. A prominent 20 kDa band was observed in all treated samples suggesting that some differential proteins could be over-expressed during heavy metal treatment and might be involved in cell resistance mechanisms.

Cadmium resistance in extremely halophilic archaeon Haloferax strain BBK2

Halophilic archaea are prevalent in highly saline habitats. Haloferax strain BBK2 is an orange pigmented, exopolysaccharide (EPS) producing extremely halophilic archaeon, isolated from solar salterns of Ribandar, Goa, India. It grew in varying pH (5-10) and NaCl concentration (10-30%). The isolate grew well in complex (NTYE) and minimal media (NGSM) in presence of heavy metal cadmium (Cd) up to 4.0 mM (805.28 mg L(-1)) concentration. The optimum growth in the presence and absence of Cd was seen at a pH range of 7-9 and salinity of 15-25%. The growth kinetics of the isolate in NTYE showed a specific growth rate (μmax) of 0.352 with generation time of 1.968 days. In presence of 1mM Cd, the μmax was 0.325 day(-1) and generation time was 2.132 days. In NGSM, the μmax decreased from 0.517 day(-1) (in control) to 0.265 day(-1) in 1mM Cd while, the doubling time increased from 1.34 days in control to 2.615 days in presence of 1 mM Cd. SDS PAGE of the whole cell protein extracts showed overexpressed proteins of 74.14 and 40 kDa. The scanning electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDX) analysis of the intact cells and cells disrupted by dialysis revealed that Cd was bound onto the cells, which was further confirmed by AAS, FTIR and XRD analysis.

Redox proteomics changes in the fungal pathogen Trichosporon asahii on arsenic exposure: identification of protein responses to metal-induced oxidative stress in an environmentally-sampled isolate

Trichosporon asahii is a yeast pathogen implicated in opportunistic infections. Cultures of an isolate collected from industrial wastewater were exposed for 2 days to 100 mg/L sodium arsenite (NaAsO₂) and cadmium (CdCl₂). Both metals reduced glutathione transferase (GST) activity but had no effect on superoxide dismutase or catalase. NaAsO₂ exposure increased glutathione reductase activity while CdCl₂ had no effect. Protein thiols were labeled with 5-iodoacetamido fluorescein followed by one dimensional electrophoresis which revealed extensive protein thiol oxidation in response to CdCl₂ treatment but thiol reduction in response to NaAsO₂. Two dimensional electrophoresis analyses showed that the intensity of some protein spots was enhanced on treatment as judged by SameSpots image analysis software. In addition, some spots showed decreased IAF fluorescence suggesting thiol oxidation. Selected spots were excised and tryptic digested for identification by MALDI-TOF/TOF MS. Twenty unique T. asahii proteins were identified of which the following proteins were up-regulated in response to NaAsO₂: 3-isopropylmalate dehydrogenase, phospholipase B, alanine-glyoxylate aminotransferase, ATP synthase alpha chain, 20S proteasome beta-type subunit Pre3p and the hypothetical proteins A1Q1_08001, A1Q2_03020, A1Q1_06950, A1Q1_06913. In addition, the following showed decreased thiol-associated fluorescence consistent with thiol oxidation; aconitase; aldehyde reductase I; phosphoglycerate kinase; translation elongation factor 2; heat shock protein 70 and hypothetical protein A1Q2_04745. Some proteins showed both increase in abundance coupled with decrease in IAF fluorescence; 3-hydroxyisobutyryl- CoA hydrolase; homoserine dehydrogenase Hom6 and hypothetical proteins A1Q2_03020 and A1Q1_00754. Targets implicated in redox response included 10 unique metabolic enzymes, heat shock proteins, a component of the 20S proteasome and translation elongation factor 2. These data suggest extensive proteomic alterations in response to metal-induced oxidative stress in T. asahii. Amino acid metabolism, protein folding and degradation are principally affected.

Selenium alleviates cadmium toxicity by preventing oxidative stress in sunflower (Helianthus annuus) seedlings

The present study investigated the possible mediatory role of selenium (Se) in protecting plants from cadmium (Cd) toxicity. The exposure of sunflower seedlings to 20μM Cd inhibited biomass production, decreased chlorophyll and carotenoid concentrations and strongly increased accumulation of Cd in both roots and shoots. Similarly, Cd enhanced hydrogen peroxides content and lipid peroxidation as indicated by malondialdehyde accumulation. Pre-soaking seeds with Se (5, 10 and 20μM) alleviated the negative effect of Cd on growth and led to a decrease in oxidative injuries caused by Cd. Furthermore, Se enhanced the activities of catalase, ascorbate peroxidase and glutathione reductase, but lowered that of superoxide dismutase and guaiacol peroxidase. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to Cd were significantly decreased by Se treatment. The data suggest that the beneficial effect of Se during an earlier growth period could be related to avoidance of cumulative damage upon exposure to Cd, thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity.

Cytoplasmic inorganic polyphosphate participates in the heavy metal tolerance of Cryptococcus humicola

The basidiomycetous yeast Cryptococcus humicola was shown to be tolerant to manganese, cobalt, nickel, zinc, lanthanum, and cadmium cations at a concentration of 2.5 mmol/L, which is toxic for many yeasts. The basidiomycetous yeast Cryptococcus terreus was sensitive to all these ions and did not grow at the above concentration. In the presence of heavy metal cations, С. humicola, as opposed to C. terreus, was characterized by the higher content of acid-soluble inorganic polyphosphates. In vivo 4',6'-diamino-2-phenylindole dihydrochloride staining revealed polyphosphate accumulation in the cell wall and cytoplasmic inclusions of С. humicola in the presence of heavy metals. In C. terreus, polyphosphates in the presence of heavy metals accumulate mainly in vacuoles, which results in morphological changes in these organelles and, probably, disturbance of their function. The role of polyphosphate accumulation and cellular localization as factors of heavy metal tolerance of Cryptococcus humicola is discussed.

Metal biosorption in lignocellulosic biofuel biorefinery effluent: an initial step towards sustainability of water resources

Biosorption of metals by microorganisms is a promising technology to remove accumulated non-process elements in highly recycled biorefinery process water. Removal of these elements would enable greater water reuse and reduce the environmental impact of effluent discharge. A model lignocellulosic ethanol biorefinery wastewater was created based on pulp mill effluent. This generated a wastewater with an environmentally realistic high loading of dissolved natural organic matter (900 mg/l), a potentially important factor influencing metal biosorption. Analysis of feedstock and pulp mill effluent indicated that Mn and Zn are likely to be problematic in highly recycled lignocellulosic ethanol biorefinery process water. Therefore, the growth of several bacteria and fungi from existing collections, and some isolated from pulp mill effluent were tested in the model wastewater spiked with Mn and Zn (0.2 mM). Wastewater isolates grew the best in the wastewater. Metal uptake varied by species and was much greater for Zn than Mn. A bacterium, Novosphingobium nitrogenifigens Y88T, removed the most metal per unit biomass, 35 and 17 mg Mn/g. No other organism tested decreased the Mn concentration. A yeast, Candida tropicalis, produced the most biomass and removed the most total metal (38 % of Zn), while uptake per unit biomass was 24 mg Zn/g. These results indicate that microorganisms can remove significant amounts of metals in wastewater with high concentrations of dissolved natural organic matter. Metal sorption by autochthonous microorganisms in an anaerobic bioreactor may be able to extend water reuse and therefore lower the water consumption of future biorefineries.

Selected enzyme activities of urban heavy metal-polluted soils in the presence and absence of an oligochaete, Lampito mauritii (Kinberg)

Soils samples collected from five different areas (S1-S5) around electroplating industries in the city of Coimbatore were analysed for the activities of selected enzymes (cellulase, phosphatase, amylase, urease, and invertase) in the presence and absence of the earthworm Lampito mauritii (Kinberg). Heavy metal analysis of soils showed that chromium (<504 mg/kg) and copper (<28.1mg/kg) contents were much higher than cadmium (<10.60 mg/kg) except in S5, where cadmium (10.6 mg/kg) was higher than the copper. Except for phosphatase, the activities of all enzymes increased with increasing period of incubation under laboratory conditions, both with and without earthworms. The results of the three-way ANOVA (effect of three factors- worms-with and without addition, soil and incubation time), however, showed that there was no significant difference between enzyme activities (with and without earthworm) and soil and incubation time for amylase and urease activity. Further, no significant difference was found between soils for cellulase activity and between all the above factors for urease activity. The results concluded that though the earthworms died at the end of the incubation period, the resultant increase or decrease in the enzymatic activity may be attributed to the metabolic activities of the worms during their lifetime in the experimental container. Also, the worms after death may have provided suitable substrate for the growth of the microorganisms thereby influencing enzyme activity.

A preconcentration procedure for the determination of cadmium in biological material after on-line cloud point extraction

In this paper, a method involving on-line preconcentration with cloud point extraction for the determination of cadmium in biological samples is presented. The procedure is based on the sorption of micelles containing Cd(II) ions and the reagent 4-(5'-bromo-2'-thiazolylazo)orcinol (Br-TAO) in a minicolumn packed with polyester. The surfactant Triton X-114 was used in the formation of micelles. After sorption, the Cd(II) ions were desorbed from the minicolumn with acid eluent and determined by flame atomic absorption spectrometry. Parameters influencing the cloud point extraction were studied. The method showed a detection limit of 0.5 μg l(-1) and an enhancement factor of 27. The accuracy was tested by determination of cadmium in certified reference materials (spinach leaves 1570a and tomato leaves 1573a) from the National Institute of Standards and Technology.