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.

Evidences for the augmented Cd(II) biosorption by Cd(II) resistant strain Candida tropicalis XTA1874 from contaminated aqueous medium

Cadmium is one of the most dreadful heavy metals and is becoming a major toxicant in ground water with increasing concentration above the WHO Guidelines in drinking water (0.003 mg/L). The potential sources of cadmium include sewage sludge, phosphate fertilizers and ingredients like Ni-Cd batteries, pigments, plating and plastics. Cadmium levels are increased in water owing to the use and disposal of cadmium containing ingredients. Water draining from a landfill may contain higher cadmium levels. The authors have tried to evaluate the optimized nutritional conditions for the optimal growth and Cd(II) remediation capacity for a developed Cd(II) resistant yeast strain named Candida tropicalis XTA 1874 isolated from contaminated water-body in West Bengal. By analyzing the optimization conditions, a synthetic medium was developed and the composition has been given in the main text. The strain showed much better Cd(II) adsorption capacity under the optimized nutritional conditions (Mean removal = 88.077 ± 0.097%).

Isolation and characterization of a highly effective bacterium Bacillus cereus b-525k for hexavalent chromium detoxification

The chromate resistant Gram-positive Bacillus cereus strain b-525k was isolated from tannery effluents, demonstrating optimal propagation at 37 °C and pH 8. The minimum inhibitory concentration (MIC) test showed that B. cereus b-525k can tolerate up to 32 mM Cr⁶⁺, and also exhibit the ability to resist other toxic metal ions including Pb²⁺ (23 mM), As³⁺ (21 mM), Zn²⁺ (17 mM), Cd²⁺ (5 mM), Cu²⁺ (2 mM), and Ni²⁺ (3 mM) with the resistance order as Cr ⁶⁺ > Pb²⁺ > As³⁺ >Zn²⁺ >Cd²⁺ >Ni²⁺ >Cu²⁺. B. cereus b-525k showed maximum biosorption efficiency (q) of 51 mM Cr⁶⁺/g after 6 days. Chromate stress elicited pronounced production of antioxidant enzymes such as catalase (CAT) 191%, glutathione transferase (GST) 192%, superoxide dismutase (SOD) 161%, peroxidase (POX) 199%, and ascorbate peroxidase (APOX) (154%). Within B. cereus b-525k, the influence of Cr⁶⁺ stress (2 mM) did stimulate rise in levels of GSH (907%) and non-protein thiols (541%) was measured as compared to the control (without any Cr⁶⁺ stress) which markedly nullifies Cr⁶⁺ generated oxidative stress. The pilot scale experiments utilizing original tannery effluent showed that B. cereus b-525k could remove 99% Cr⁶⁺ in 6 days, thus, it could be a potential candidate to reclaim the chromate contaminated sites.

Characterization of cadmium-tolerant endophytic fungi isolated from soybean (Glycine max) and barley (Hordeum vulgare)

Cadmium stress disrupts plant-microbial interactions and reduces plant growth and development. In plants, the tolerance to stress can be increased by inoculation with endophytic microorganisms. The aim of this study was to investigate the distribution of endophytic fungi in various plant organs of barley and soybean and evaluate their Cd removal ability. Two hundred fifty-three fungal strains were isolated from various organs of barley (Hordeum vulgare cv Arna) and soybean (Glycine max cv Almaty). The colonization rate ranged from 13.6% to 57.3% and was significantly higher in the roots. Ten genera were identified: Fusarium, Penicillium, Aspergillus, Metarhizium, Beauveria, Trichoderma, Rhodotorula, Cryptococcus, Aureobasidium and Metschnikowia. Twenty-three fungal strains have a Cd tolerance index from 0.24 to 1.12. Five strains (Beauveria bassiana T7, Beauveria bassiana T15, Rhodotorula mucilaginosa MK1, Rhodotorula mucilaginosa RH2, Metschnikowia pulcherrima MP2) with the highest level of Cd tolerance have minimum inhibitory concentrations from 290 to 2400 μg/ml. These fungi were able to remove Cd up to 59%. The bioaccumulation capacity ranged from 2.3 to 11.9 mg/g. Selected fungal strains could be considered as biological agents for their potential application in the bioremediation of contaminated sites.

Removal of Manganese and Copper from Aqueous Solution by Yeast Papiliotrema huenov

Papiliotrema huenov was previously reported to be highly tolerant of a range of extremely toxic heavy metals. This study aimed to identify the potential of P. huenov to remove manganese and copper from aqueous solution. Physical conditions which affect removal of Mn(II) and Cu(II) were determined. Optimal temperature for adsorption of both metal ions was 30 °C, and optimal pH for maximum uptake of Mn(II) and Cu(II) were 5 and 6, respectively. Under these conditions, living cells of P. huenov accumulated up to 75.58% of 110 mg/L Mn(II) and 70.5% of 128 mg/L Cu(II) over 120 h, whereas, the removal efficiency of metal ions by dead cells over 1 h was 60.3% and 56.5%, respectively. These results indicate that living cells are more effective than dead biomass for bioremediation, but that greater time is required. The experimental data extends the potential use of P. huenov in biosorption and bioaccumulation of toxic heavy metals to copper and manganese, two of the most common industrial contaminants.

Comparative behavior of two gram positive Cr6+ resistant bacterial strains Bacillus aerius S1 and Brevibacterium iodinum S2 under hexavalent chromium stress

Bacillus aerius S1 and Brevibacterium iodinum S2 showed maximum growth at 37 °C and pH 8. B. aerius and B. iodinum could resist Cr6+ upto 30 and 35 mM and biosorption proficiency (q) of B. aerius S1 was 19, 27, 52 and 34 mM/g while for B. iodinum S2, it was 39, 50, 23 and 16 mM/g mM/g after 2, 4, 6 and 8 days of incubation. A pronounced rise in antioxidant enzymes activities was determined in B. aerius S1 i.e. POX (963%), CAT (717%), APOX (699%), SOD (683%), and GST (792%). However, in B. iodinum S2, relatively a minor increase was estimated. A significant GSH increase was determined in B. aerius S1 (364%) and B. iodinum S2 (663%) cultures under 2 mM Cr6+ stress. Pilot scale study demonstrated that both strains could reduce Cr6+ into Cr3+ within 6 days from the original tannery effluent with efficiency of 99%.

Isolation of lead-resistant Arthrobactor strain GQ-9 and its biosorption mechanism

In this study, lead-resistant bacterium Arthrobacter sp. GQ-9 with a resistant capability to cadmium, zinc, and copper was isolated from a heavy metal polluted soil. Microcalorimetry analysis was applied to assess the strain's microbial activity under Pb(II) stress and suggested that GQ-9's microbial activities under Pb(II) stress were stronger than a non-resistant strain. Biosorption batch experiments revealed that the optimal condition for adsorption of Pb(II) by GQ-9 was pH 5.5, a biomass dosage of 1.2 g L^-1, and an initial Pb(II) concentration of 100 mg L^-1 with a maximum biosorption capacity of 17.56 mg g^-1.Adsorption-desorption experiments and Fourier transform infrared spectroscopy (FTIR) analysis were applied to elucidate the biosorption mechanisms. Adsorption-desorption analysis showed that GQ-9 cells could sequester 56.60% of the adsorbed Pb(II) ions on the cell wall. FTIR analysis suggested that hydroxyl, carboxyl, amino, nitrile, and sulfhydryl groups and amide I, amide II bands on the GQ-9 cell wall participated in the complexation of Pb(II) ions. The present study illustrates that the lead-resistant bacteria GQ-9 has the potential for further development of an effective and ecofriendly adsorbent for heavy metal bioremediation.

The SNP rs10911021 is associated with oxidative stress in coronary heart disease patients from Pakistan

BACKGROUND

rs10911021 (a single nucleotide polymorphism present upstream of the GLUL gene) affects glutamic acid metabolism, and was shown to be associated with coronary heart disease (CHD) in patients with T2DM but a definite mechanism is unknown. It may affect glutathione cycle, an important effector in the antioxidant defense mechanism, in the cells. We checked the association of this SNP with CHD and oxidative stress biomarkers, malondialdeheyde (MDA), GSH and GSSG in Pakistani patients.

METHODS

A total of 650 subjects (425 CHD cases and 225 controls) were genotyped by TaqMan allelic discrimination technique. The levels of MDA, GSH and GSSG were measured by standard protocols.

RESULTS

The risk allele frequency was higher in cases than controls, but the difference was insignificant (p = 0.55). The SNP was not associated with CHD (p = 0.053) but when the analysis was limited to CHD patients having DM, a significant association (p = 0.03) was observed. The blood levels of MDA and GSSG were higher while that of GSH was significantly lower in the cases than the controls (p < 0.05). Each risk allele increased MDA and GSSG by 0.29 (0.036) mmol/l and 0.4 (0.04) mmol/l, respectively, while decreased GSH by -0.36 (0.03) mmol/l. The SNP was not associated with any of the tested blood lipids.

CONCLUSION

The SNP rs10911021 was associated with CHD only in patients having diabetes, but the SNP was associated with total oxidative stress biomarkers MDA and GSH and GSSG levels. As the SNP rs10911021 showed significant association with oxidative stress parameters and these parameters should an increased oxidative stress in the CHD subjects, it can be concluded that the SNP may have contributed to increase the risk of heart diseases in the diabetic subjects by increasing the oxidative stress.

Identification of cadmium-resistant fungi related to Cd transportation in bermudagrass [Cynodon dactylon (L.) Pers]

Phytoremediation utilizing plants and microbes has been increasingly adopted as a green technology for cleaning up heavy metal polluted soils. Cd polluted soil and native bermudagrass from Liuyang and Zhuzhou in Hunan province of China were collected to investigate microbial diversity and isolate Cd resistant fungi, and then to determine the effect of Cd resistant fungi on Cd tolerance and transportation of bermudagrass. The functional diversity of microorganisms was evaluated using the BIOLOG Eco method. Cd-resistant fungi strain was isolated and identified as Aspergillus aculeatus based on the ribosomal internal transcribed spacer region sequence analysis. Bermudagrass was exposed to control, Cd only, and Cd plus A. aculeatus (Cd + A. aculeatus) with growth matrix (sawdust/sand = 3/1 in volume). Results indicated that Cd + A. aculeatus treated bermudagrass exhibited a higher photosynthetic activity compared to Cd only treated plants. Inoculation of A. aculeatus resulted in a decrease in stem and leaf Cd concentrations, to a greater extent for Cd-sensitive than for Cd-tolerant genotype. However, inoculation of A. aculeatus increased root Cd concentration under Cd stress conditions, significantly elevated soil pH, and decreased soil water-soluble Cd concentration. These results suggested that A. aculeatus might be potentially applied to improve Cd tolerance and to reduce Cd transportation to shoot of bermudagrass.

Cadmium-resistance mechanism in the bacteria Cupriavidus metallidurans CH34 and Pseudomonas putida mt2

Cupriavidus metallidurans CH34 and Pseudomonas putida mt2 were used as cadmium (Cd)-resistant and -sensitive bacteria, respectively, to study Cd uptake, sorption, intracellular accumulation, metallothionein (MT) induction, and bioremediation potential of both isolates. According to this research work, Cd had a stimulatory effect on the growth of CH34 cells (OD578 = 1.43) compared with mt2 cells (OD578 = 0.8). Addition of N,N'-dicyclohexylcarbodiimide (DCCD) and 2,4-dinitrophenol (DNP) along with Cd resulted in more cell growth in mt2 (OD578 = 0.71) compared with CH34 (OD578 = 0.34). DCCD and DNP inhibited this active uptake only in CH34 but not in mt2. Greater Cd interaction with the cell surface was observed in mt2 cells compared with CH34 cells. Intracellular Cd accumulation was interrupted by DCCD and DNP in CH34 (only 1.81 ± 0.04 μg L(-1) at 5 h) but not in mt2 (24.41 ± 0.01 μg L(-1) at 5 h). Intracellular Cd uptake was observed in even killed mt2 cells (7.11 ± 0.05 μg L(-1) at 5 h) compared with CH34 cells (2.50 ± 0.08 μg L(-1) at 5 h). This result showed that the Cd accumulation mechanism in CH34 is ATPase-dependent, whereas in mt2 uptake mechanism is not ATPase-dependent because mt2 ATPase was not inhibited by DCCD and DNP. CH34 removed 93 mg L(-1) of Cd after 8 days from original industrial effluent, which was more than Cd removal by CH34 from distilled water (i.e. 90 mg L(-1) after 8 days). mt2 was able to remove 80 mg L(-1) of Cd after 8 days from original industrial effluent, which was more than Cd removal by mt2 from distilled water (i.e. 77 mg L(-1) after 8 days). Cd did not induce any MT in CH34, but it did so in mt2 (14 kDa), which was thought to be a Cd-resistance mechanism operative in mt2.

Antioxidative enzyme profiling and biosorption ability of Cupriavidus metallidurans CH34 and Pseudomonas putida mt2 under cadmium stress

Cupriavidus metallidurans CH34 and Pseudomonas putida mt2 were used as cadmium (Cd)-resistant and -sensitive bacteria, respectively, to study their biosorption ability and their antioxidative enzymes. The minimal inhibitory concentration of C. metallidurans CH34 for Cd was found to be 30 mM, and for P. putida mt2 it was 1.25 mM. The tube dilution method revealed the heavy-metal resistance pattern of C. metallidurans CH34 as Ni(2+) (10 mM)>Zn(2+) (4 mM)>Cu(2+) (2 mM)>Hg(2+) (1 mM)>Cr(2+) (1 mM)>Pb(2+) (0 mM), whereas P. putida mt2 was only resistant to Zn(2+) (1 mM). Under Cd stress, the induction of GSH was higher in C. metallidurans CH34 (0.359 ± 0.010 mM g(-1)  FW) than in P. putida mt2 (0.286 ± 0.005 mM g(-1)  FW). Glutathione reductase was more highly expressed in the mt2 strain, in contrast to non-protein thiols and peroxidase. Unlike dead bacterial cells, live cells of both bacteria showed significant Cd biosorption, i.e. more than 80% at 48 h. C. metallidurans CH34 used only catalase, whereas P. putida mt2 used superoxide dismutase and ascorbate peroxidase to combat Cd stress. This study investigated the Cd biosorption ability and enzymes involved in the Cd detoxification mechanisms of C. metallidurans CH34 and P. putida mt2.

Biosorption of heavy metals by lactic acid bacteria and identification of mercury binding protein

Heavy metals cause various health hazards. Using lactic acid bacteria (LAB), we tested the biosorption of heavy metals e.g. cadmium (Cd) (II), lead (Pb) (II), arsenic (As) (III), and mercury (Hg) (II). Cd (II) sorption was tested in 103 strains using atomic absorption spectrophotometery (AAS). Weissella viridescens MYU 205 (1 × 10(8) cells/ml) decreased Cd (II) levels in citrate buffer (pH 6.0) from one ppm to 0.459 ± 0.016 ppm, corresponding to 10.46 μg of Cd (II). After screening, 11 LAB strains were tested using various pH (pH 4.0, 5.0, 6.0, 7.0) showing the sorption was acid sensitive; and was cell concentration dependent, where the Cd (II) concentration decreased from one ppm to 0.042 (max)/0.255 (min) ppm at 1 × 10(10) cells/ml. Additionally, the biosorption of Pb (II), As (III), and Hg (II) were tested using an inductively coupled plasma mass spectrometer (ICP-MS). The Hg (II) concentration was reduced the most followed by Pb (II) and As (III). Many of the bacterial cell surface proteins of W. viridescens MYU 205 showed binding to Hg (II) using the Hg (II) column assay. Having a CXXC motif, a ∼14 kDa protein may be one of the Hg (II) binding proteins. LAB biosorption may aid the detoxification of people exposed to heavy metals.