Metal Stress Conditions Research Articles

Heavy metal stress induces adaptative responses in the liverwort Conocephalum conicum L. (Dum.): An integrated biologic and metabolomic study

Bioaccumulation, ultrastructural and DNA damage, oxidative stress, and metabolomic analyses were carried out in vitro on the liverwort Conocephalum conicum L. in response to the heavy metal concentrations measured in two sites along the Sarno river (C1 and C2) representative of two different environmental conditions. Bioaccumulation and bioconcentration data confirm C. conicum is a good bioindicator. Our TEM observations showed typically preserved ultrastructure of the chloroplasts in C1 samples, nearly identical to the chloroplasts of the control sample (CTRL; freshly collected and not exposed), whereas in C2 samples they appeared misshaped, swollen and with poorly developed thylakoids in a rather clear stroma. DNA damage, antioxidant enzymatic activity, ROS production and localization showed no difference between CTRL and C1 samples, instead significant differences between C1 and C2 samples. In addition, in this study, we used for the first time the untargeted MS-based molecular networking to examine the role of heavy metal stress in the differential production of the secondary metabolites (SM) in C. conicum. Metabolome analysis evidenced no changes between CTRL and C1 samples, instead a dramatic change in SM production under metal stress conditions, in particular a remodeling of the lipid metabolism through the production of members of betaine and oxidated lipid classes, as well as production of flavonoids was observed. All the occurred variations respond consistently with the heavy metal concentration trend so we can propose them as pollution biomarkers.

The molecular characteristics of two metallothioneins in Ostrinia furnacalis and expression under conditions of heavy metal stress

• Two metallothionein genes from Ostrinia furnacalis were cloned and identified. • Cd, Cu and Zn inhibit the expression of OfMT1 of Ostrinia furnacalis . • Cd and Cu induce the expression of OfMT2 of Ostrinia furnacalis . Metallothioneins are ubiquitously-expressed metal-binding proteins. Despite their potential ecological relevance, no prior reports have identified any metallothioneins in Ostrinia furnacalis or other Lepidoptera species. A better understanding of the molecular characteristics and regulatory dynamics of metallothionein genes in O. furnacalis under heavy metal stress conditions would enable future studies of the roles played by these proteins in the context of heavy metal detoxification. Herein, we identified and characterized two metallothionein ( OfMT ) genes in O. furnacalis, including the 147 bp OfMT1 gene encoding a 48 amino acid protein containing 10 cysteine residues, and the 141 bp OfMT2 gene encoding a 46 amino acid protein containing 12 cysteine residues. The expression of OfMT2 was found to be related to Cu and Cd concentrations in a dose-dependent manner but was unaffected by Zn exposure. Overall, these results indicate that OfMT genes likely encode metal-binding proteins consistent with their potential role in the maintenance of heavy metal homeostasis.

In situ mapping of ion distribution profiles and gene expression reveals interactions between hypoxia and Mn2+/Fe2+ availability in barley roots

Flooding stress affects soil properties thus altering the availability, uptake, and transport of mineral nutrients in plant roots. Flooding stress also increases the amount of soluble Mn2+ and Fe2+ in the soil and their uptake by plants, causing elemental toxicity. However, as oxygen profiles in plant roots are not uniform, it is still unclear how soil flooding will affect Mn2+/Fe2+ absorption and distribution in different cell types and tissues. In this study, waterlogging sensitive barley variety NasoNijo (NN) and tolerant variety TX9425 (TX) were exposed to hypoxia, metal (Mn2+ and Fe2+), and combined hypoxia + metal treatment to map the in situ ion profiles at different regions of barley root. We found that combined hypoxia and metal stress causes significantly more reduction in plant biomass compared with the single submergence or metal stress. Despite this, more Fe and Mn were accumulated under metal stress condition than those under combined stress, regardless of variety. Cultivar NN absorbed more Fe and Mn than TX in the cortical cells of the root meristem and in the mature zone under metal stress which was also verified by histochemical detection. In the mature zone, the expressions of Fe and Mn transporter genes including HvADPRibase-Mn (Manganese-dependent ADP-ribose), HvZIP1 (zinc-regulated transporter /Fe-regulated transporter-like protein 1), HvYS1 (yellow stripe 1), HvNRAMP5 (Natural Resistance-Associated Macrophage Protein 5) were significantly downregulated under all three treatments in both barley varieties except HvADPRibase-Mn HvZIP1 cortex of TX were unchanged under metal stress. Interestingly, the transcripts of HvMTP1 (metal tolerance protein 1) were significantly downregulated by metal and combined stress in stele and upregulated by hypoxia and metal stress in cortex of TX, but not affected in NN. It is concluded that Fe and Mn absorption involving HvMTP1is associated with the extent of waterlogging tolerance in barley.

Phytohormones enhance heavy metal responses in Euglena gracilis: Evidence from uptake of Ni, Pb and Cd and linkages to hormonomic and metabolomic dynamics

Over the last decade, significant effort has been made to understand phytohormonal functions (e.g., cytokinins (CKs) and abscisic acid (ABA)) in metal stress responses of higher plants and algae. Despite the potential for these phytohormones to improve industrial remediation by Euglena gracilis (Euglenophyceae), no such roles have been elucidated for this highly adaptive species and its response to heavy metals. This study demonstrates that toxic metals (nickel, lead, cadmium) modify hormonal activity profiles (i.e., CK forms and their concentrations) in E. gracilis. Furthermore, exogenous ABA or CK (tZ) enabled higher metal uptake efficiency (i.e., 9.35% in lead and 9.2% in cadmium uptake with CK) and alleviated metal toxicity through the regulation of endogenous CKs (i.e., total CK, isoprenoid CK) and gibberellin (GAs, GA1 and GA3) levels. These responses suggest that E. gracilis regulates multiple phytohormone signals during metal stress acclimation. A deeper approach, using untargeted metabolomic analyses, gave more detailed insight into phytohormone-controlled pathways and associated modified metabolites, which were frequently related to metal accumulation and the physiological acclimation to metal presence. Significant changes in the levels of cellular metabolites, especially those involved in acclimation to metal stress, were under the influence of phytohormones in algal cells. When grown under metal stress conditions, the presence of exogenous ABA or CKs, caused changes in cellular metabolites which included those from: lipid pathways, riboflavin metabolism, the biosynthesis of cofactors/vitamins, and carbohydrate metabolism. Also, bioactive secondary metabolites (e.g., terpenoids, alkaloids, flavonoids, carotenoids) were modified in algal cells treated with phytohormones. Thus, the study gives a detailed view on the regulatory functions of ABA and CKs in algal metal bioremediation strategies, which are attributed to enhanced metal uptake and in the fine-tuning of plant hormone levels during metal stress response. The results can guide efforts to develop efficient, low-cost and environmentally friendly methods for bioremediation.

OsGLP participates in the regulation of lignin synthesis and deposition in rice against copper and cadmium toxicity.

Copper (Cu) and cadmium (Cd) are common heavy metal pollutants. When Cd and excessive Cu accumulate in plants, plant growth is reduced. Our previous study showed that Germin-like proteins (GLPs), which exist in tandem on chromosomes, are a class of soluble glycoproteins that respond to Cu stress. In this study, hydroponic cultures were carried out to investigate the effect of GLP on Cd and Cu tolerance and accumulation in rice. The results showed that knockout of a single OsGLP8-2 gene or ten OsGLP genes (OsGLP8-2 to OsGLP8-11) resulted in a similar sensitivity to Cd and Cu toxicity. When subjected to Cu and Cd stress, the glp8-2 and glp8-(2-11) mutants displayed a more sensitive phenotype based on the plant height, root length, and dry biomass of the rice seedlings. Correspondingly, Cu and Cd concentrations in the glp8-2 and glp8-(2-11) mutants were significantly higher than those in the wild-type (WT) and OsGLP8-2-overexpressing line. However, Cu and Cd accumulation in the cell wall was the opposite. Furthermore, we determined lignin accumulation. The overexpressing-OsGLP8-2 line had a higher lignin accumulation in the shoot and root cell walls than those of the WT, glp8-2, and glp8-(2-11). The expression of lignin synthesis genes in the OsGLP8-2-overexpressing line was significantly higher than that in the WT, glp8-2, and glp8-(2-11). The SOD activity of OsGLP8-2, Diaminobe-nzidine (DAB), propidium iodide (PI) staining, and Malondialdehyde (MDA) content determination suggested that OsGLP8-2 is involved in heavy metal-induced antioxidant defense in rice. Our findings clearly suggest that OsGLPs participate in responses to heavy metal stress by lignin deposition and antioxidant defense capacity in rice, and OsGLP8-2 may play a major role in the tandem repeat gene clusters of chromosome 8 under heavy metal stress conditions.

Effects of root exudates of Vetiver on physicochemical properties and fractionation of heavy metals in tannery effluent contaminated soil

A range of organic substances, referred to as root exudates can be released by plant roots either actively or passively which are the notable source for microbial growth in the root zone and also involved in nutrient cycling and mineralisation of organics thus they could possibly influence the degradation of contaminants in the rhizosphere. The key components of the root exudates of vetiver are total carbohydrates, reducing sugars, total phenolics, flavonoids, total alkaloids, organic acids and total proteins. The organic acids are found in significantly higher amount under heavy metal stress conditions. On addition of this root exudates manually for a period of 60 days yielded in alteration in the physico-chemical properties of the soil and fractionation of chromium and lead – the representative contamiants present in the experimental soil which was collected from the tannery effluent polluted areas of Vellore, Tamil Nadu. The pH and organic carbon content in the soil is increased while the electrical conductivity got decreased. The root exudates application possibly increased the bioavailability of the heavy metals besides reducing the residual form which paves the way for easier remediation of such metals since their availability got increased. The positive effect of root exudates of vetiver provided a new idea to remediate the contaminated soils.

Nanovesicle and extracellular polymeric substance synthesis from the remediation of heavy metal ions from soil

Heavy metal toxicity affects aquatic plants and animals, disturbing biodiversity and ecological balance causing bioaccumulation of heavy metals. Industrialization and urbanization are inevitable in modern-day life, and control and detoxification methods need to be accorded to meet the hazardous environment. Microorganisms and plants have been widely used in the bioremediation of heavy metals. Sporosarcina pasteurii, a gram-positive bacterium that is widely known for its calcite precipitation property in bio-cementing applications has been explored in the study for its metal tolerance ability for the first time. S. pasteurii SRMNP1 (KF214757) can tolerate silver stress to form nanoparticles and can remediate multiple heavy metals to promote the growth of various plants. This astounding property of the isolate warranted extensive examinations to comprehend the physiological changes during an external heavy metal stress condition. The present study aimed to understand various physiological responses occurring in S. pasteuriiSRMNP1 during the metal tolerance phenomenon using electron microscopy. The isolate was subjected to heavy metal stress, and a transmission electron microscope examination was used to analyze the physiological changes in bacteria to evade the metal stress. S. pasteurii SRMNP1 was tolerant against a wide range of heavy metal ions and can withstand a broad pH range (5–9). Transmission Electron Microscopy (TEM) examination of S. pasteurii SRMNP1 followed by 5 mM nickel sulfate treatment revealed the presence of nanovesicles encapsulating nanosized particles in intra and extracellular spaces. This suggests that the bacteria evade the metal stress by converting the metal ions into nanosized particles and encapsulating them within nanovesicles to efflux them through the vesicle budding mechanism. Moreover, the TEM images revealed an excessive secretion of extracellular polymeric substances by the strain to discharge the metal particles outside the bacterial system. S. pasteurii can be foreseen as an effective bioremediation agent with the potential to produce nanosized particles, nanovesicles, and extracellular polymeric substances. This study provides physiological evidence that, besides calcium precipitation applications, S. pasteurii can further be explored for its multidimensional roles in the fields of drug delivery and environmental engineering.

Effect of polyamines and zeolites on the protein profile of leaves of the date palm cuttings Phoenix dactylifera L. grown under heavy metal stress conditions

This study was conducted on the five to six years old offshoots of date palm (Jebjab) cultivar planted in sustainable land, using an environment contaminated with heavy elements, with irrigation water contaminated with heavy elements Pb(NO3)2 300 mg.kg-1 and cadmium chloride CdCl2 3 mmol, as well as the comparison treatment. Then the treatment was with some polyamine compounds Putrescine 500 mg L-1, coumaric acid 500 mg L-1, and a zeolite compound at a rate of 10 kg Palm-1, in addition to the comparison treatment in the form of ground addition to the soil of the off shoots samples were taken from palm fronds, samples were dried using Freeze-dryer (Lyophilization technique), the protein was extracted from samples, and protein migration was carried out on Polyacrylamide gel using Slab-Electrophoresis method in the presence of SDS denaturants. The molecular weights of proteins were estimated and plotted using PhotoCapt Mw. The results of the study showed that the protein pattern of the leaves show up that all the trees of the study had taken part (identical) with the first protein bundle and the fifth protein bundle on the polyacrylamide gel, as the molecular weights of the proteins of the first bundle ranged between (222.136-243.750) kDa, while the molecular weights of the proteins of the bundle ranged. The fifth is between (24.843-50.386) kDa. This coincidence or participation in the molecular weights of the protein bundles of all the study trees may indicate that these trees belong to one plant origin (which is the Jebjab variety), as these plants share close molecular weights. Keywords: Date Palm, molecular weights, polyacrylamide gel, polyamine compounds.

Arsenic resistance and horizontal gene transfer are associated with carbon and nitrogen enrichment in bacteria

Coastal waters are confluences receiving large amounts of point and non-point sources of pollution. An attempt was made to explore microbial community interactions in response to carbon, nitrogen and metal pollution. Additionally, experiments were designed to analyze the influence of these factors on horizontal gene transfer (HGT). Shift in bacterial diversity dynamics by arsenic stress and nutrient addition in coastal waters was explored by metagenomics of microcosm setups. Phylogenetic analysis revealed equal distribution of Gammaproteobacteria (29%) and Betaproteobacteria (28%) in control microcosm. This proportional diversity from control switched to unique distribution of Gammaproteobacteria (44.5%)> Flavobacteria (17.7%)> Bacteriodia (11.92%)> Betaproteobacteria (11.52%) in microcosm supplemented with carbon, nitrogen and metal (C + N + M). Among metal-stressed systems, alpha diversity analysis indicated highest diversity of genera in C + N + M followed by N + M > C+M> metal alone. Arsenic and ampicillin sensitive E. coli XL1 blue and environmental strains (Vibrio tubiashii W85 and E. coli W101) were tested for efficiency of uptake of plasmid (P) pUCminusMCS (arsBRampR) under varying stress conditions. Transformation experiments revealed that combined effect of carbon, nitrogen and metal on horizontal gene transfer (HGT) was significantly higher (p < 0.01) than individual factors. The effect of carbon on HGT was proved to be superior to nitrogen under metal stressed conditions. Presence of arsenic in experimental setups (P + M, P + N + M and P + C + M) enhanced the HGT compared to non-metal counterparts supplemented with carbon or nitrogen. Arsenic resistant bacterial isolates (n = 200) were tested for the ability to utilize various carbon and nitrogen substrates and distinct positive correlation (p < 0.001) was found between arsenic resistance and utilization of urea and nitrate. However, evident positive correlation was not found between carbon sources and arsenic resistance. Our findings suggest that carbon and nitrogen pollution in aquatic habitats under arsenic stress determine the microbial community dynamics and critically influence uptake of genetic material from the surrounding environment.

Biosorbents Removed Copper Heavy Metal from Agricultural Land Cultivated with Vigna radiata (Mung Bean)

Background. Heavy metals in excessive levels are hazardous to ecosystems as they can bioaccumulate in organisms, have toxic effects on biota, and even cause mortality in most life forms. Methodology. The present study consists of two studies; initially, different concentrations of copper were biosorbed by using 1 gm powder of various biosorbents such as orange peels (OP), pomegranate peels (POP), and peanut peels (PP). Furthermore, the biosorbed water was used to irrigate soil when the mung beans were cultivated. The growth parameters of plants growing under induced copper stress and treated with different bioabsorbed waters were also evaluated. Results. The results revealed that, among all biosorbents, the copper biosorption capacity of orange peels was maximum (90%), followed by pomegranate peel. The results of the second experiment exhibited that the plants irrigated with biosorbed water did not show metal toxicity. A remarkable increase in shoot length, shoot fresh weight, and shoot dry weight was observed (29.8 cm, 15.4 g, and 14 g, respectively) when exposed to biosorbent water with peanut peels + 200 mg kg−1 (Cu2+). Similarly, pomegranate peel biosorbed water turned out to be an effective treatment to enhance root length, root fresh weight, and root dry weight (6.81 cm, 4.07 g, and 2.66 g, respectively) and resist against induced heavy metal stress conditions at higher concentration (200 mg kg−1). Furthermore, orange peel biosorbed water elevated the total chlorophyll content and soluble sugar content in mung bean (1.56 mg/g and 1.89 mg/g). The highest tolerance index of mung bean plant grown under the stress of Cu2+ metal was induced by orange peel biosorbed water. Conclusion. Biosorption is an environmentally friendly approach to mitigate heavy metals from the water. The studies showed that agricultural wastes have enough bioabsorption potential and should be used to absorb the heavy metal present in water.

Proteomic analysis of a copper mine isolated fungus Rhizopus microspores IOC 4686 when exposed to copper sulfate

The fungus Rhizopus microsporus, known for its absorption capacity for toxic metals was used to understand the green metal recovery via analysis of its physiology under metal stress conditions through proteomic methods. To investigate the effects of copper stress on fungus, R. microsporus IOC 4686, isolated from the mine environment, was exposed to copper ions (50mgL-1) for 48 h. This study was performed only on copper exposure. Tryptic and chymotryptic extracts of proteins were analyzed by nano- liquid chromatography-tandem mass spectrometry, identification was performed by PEAKS Studio 8.5. Proteins were classified according to their molecular function and biological process. Enzymes, such as catalase, superoxide dismutase, and cytochrome c peroxidase were found in the presence and absence of copper ions. However, only in presence of copper ions, was observed the presence of heat shock proteins (HPS 20, HPS 70, and HPS 78) and metalloproteins (GrpE protein homolog and cytochrome P450). These classes of proteins have been produced by cells in response to stress conditions. The control group (absence of copper ions) also presented antioxidant enzymes suggesting that the fungus isolated from the mine environment already has adapted to the copper. The presence of these proteins suggested a physiological response of R. microsporus IOC 4686 to oxidative stress induced by copper.

Stress mitigation strategies of plant growth-promoting rhizobacteria: Plant growth-promoting rhizobacteria mechanisms

One of the major challenges that the world is facing currently is the inadequate amount of food production with high nutrient content in accordance with the increase in population size. Moreover, availability of cultivable area with fertile soil is reducing day by day owing to ever increasing population. Further, water scarcity and expensive agricultural equipment have led to the use of agrochemicals and untreated water. Excessive use of chemical fertilizers to increase crop yield have resulted in deleterious effects on the environment, health and economy, which can be overcome to a great extent by employing biological fertilizers. There are various microbes that grows in the rhizospheric region of plants known as plant growth-promoting rhizobacteria (PGPR). PGPR act by direct and indirect modes to stimulate plant growth and improve stress reduction in plants. PGPRs are used for potential agriculture practices having a wide range of benefits like increase in nutrients content, healthy growth of crops, production of phytohormones, prevention from heavy metal stress conditions and increase in crop yield. This review reports recent studies in crop improvement strategies using PGPR and describes the mechanisms involved. The potential mechanisms of PGPR and its allies pave the way for sustainable development towards agriculture and commercialization of potential bacteria.

Exogenous Application of Salicylic Acid and Hydrogen Peroxide Ameliorate Cadmium Stress in Milk Thistle by Enhancing Morpho-Physiological Attributes Grown at Two Different Altitudes.

Cadmium (Cd+2) is a potential and widespread toxic environmental pollutant, mainly derived from a rapid industrial process that has inhibitory effects on growth, physiological, and biochemical attributes of various plant species, including medicinal plants such as Silybum marianum L. Gaertn commonly known as milk thistle. Plant signaling molecules, when applied exogenously, help to enhance/activate endogenous biosynthesis of potentially important signaling molecules and antioxidants that boost tolerance against various abiotic stresses, e.g., heavy metal stress. The present study documented the protective role of salicylic acid (SA;0.25 μM) and hydrogen peroxide (H2O2; 10 μM) priming, foliar spray, and combinational treatments in reducing Cd+2 toxicity (500 μM) in milk thistle grown at two diverse ecological zones of Balochistan Province of Pakistan i.e., Quetta (Qta) and Turbat (Tbt). The morpho-physiological and biochemical attributes of milk thistle were significantly affected by Cd+2 toxicity; however, priming and foliar spray of SA and H2O2 significantly improved the growth attributes (root/shoot length, leaf area, and root/shoot fresh and dry weight), photosynthetic pigments (Chl a, b, and carotenoids) and secondary metabolites (Anthocyanin, Soluble phenolics, and Tannins) at both altitudes by suppressing the negative impact of Cd+2. However, the oxidative damage parameters, i.e., MDA and H2O2, decreased astonishingly under the treatment of signaling molecules, thereby protecting membrane integrity under Cd+2 stress. The morphological variations were profound at the low altitude (Tbt) as compared to the high altitude (Qta). Interestingly, the physiological and biochemical attributes at both altitudes improved under SA and H2O2 treatments, thus hampered the toxic effect of Cd+2. These signaling compounds enhanced tolerance of plants under heavy metal stress conditions with the consideration of altitudinal, and ambient temperature variations remain to be the key concerns.

Consequences of copper and lead stress on biochemical properties and mitotic chromosomal behavior of two thelypteroid ferns and their potential in tolerance of those metals

The present study was undertaken to investigate the consequences of copper (Cu) and lead (Pb) stress on biochemical properties and mitotic chromosomal behavior of Thelypteris interrupta (Wild.) K. lwats and Thelypteris dentata (Forssk.) E. P. St. John. and their efficiency to accumulate and tolerate those metals. The plants were planted in pots containing different concentrations (0, 50, 100, 500 and 1000 mg kg−1) of Cu and Pb salts in the soil and were incubated for 20 weeks. Cu and Pb accumulation by both the ferns was found to be increased with increasing metal concentrations. In case of T. interrupta, maximum accumulation of Cu and Pb in the above ground part found were 68.73 mg kg−1 DW and 35.87 mg kg−1 DW respectively while in the underground part they were 127 mg kg−1 DW and 215.4 mg kg−1 DW. On the other hand, T. dentata had maximum Cu and Pb accumulation in the above ground part were 35.5 mg kg−1 DW 44.87 mg kg−1 DW, and in the underground part, they were recorded as 117.2 and 184 mg kg−1 DW respectively. A gradual increase in antioxidative enzymes (peroxidase, superoxide dismutase and catalase) with increasing metal dose was observed. However, no significant change was found in case of catalase activity in T. interrupta. Both metals exerted a negative effect on the mitotic index of both studied ferns and resulted in different types of mitotic chromosomal abnormalities. Nonetheless, antioxidative defense system of plants got activated due to heavy metal stress condition that eventually conferred protection against oxidative stress. Both the studied ferns seemed to be good accumulators and tolerant to Cu and Pb.

Potential Antioxidant and Anticancer Activities of Secondary Metabolites of Nostoc linckia Cultivated under Zn and Cu Stress Conditions

The objective of the present study is to determine the antioxidant and anticancer activities of Nostoc linckia extracts cultivated under heavy metal stress conditions (0.44, 0.88, and 1.76 mg/L for zinc and 0.158, 0.316, 0.632 mg/L for copper). Phycobiliprotein, phenolic compounds, flavonoids, and tannins were measured. Active ingredients of extracts were evaluated by GC-mass spectroscopy. The obtained results revealed that higher zinc and copper concentrations showed growth inhibition while 0.22 mg/L (Zn) and 0.079 mg/L (Cu) enhanced growth, reaching its maximum on the 25th day. Increases in catalase, lipids peroxidation, and antioxidants, as well as tannins and flavonoids, have been induced by integration of 0.88 mg/L (Zn) and 0.316 mg/L (Cu). Elevation of Zn concentration induced augmentation of antioxidant activity of crude extract (DPPH or ABTS), with superior activity at 0.44 mg/L zinc concentration (81.22%). The anticancer activity of Nostoc linckia extract (0.44 mg/L Zn) tested against four cancer cell lines: A549, Hela, HCT 116, and MCF-7. The extract at 500 µg/mL appeared the lowest cell viability of tested cell lines. The promising extract (0.44 mg/L Zn) recorded the lowest cell viability of 25.57% in cervical cell line, 29.74% in breast cell line, 33.10% in lung cell line and 34.53% in the colon cell line. The antioxidant active extract showed significant stability against pH with attributed increase in antioxidant activity in the range between 8–12. The extract can be used effectively as a natural antioxidant and anticancer after progressive testing.

Stress Driven Discovery of Natural Products From Actinobacteria with Anti-Oxidant and Cytotoxic Activities Including Docking and ADMET Properties.

Elicitation through abiotic stress, including chemical elicitors like heavy metals, is a new technique for drug discovery. In this research, the effect of heavy metals on actinobacteria Streptomyces sp. SH-1312 for secondary metabolite production, with strong pharmacological activity, along with pharmacokinetics profile, was firstly investigated. The optimum metal stress conditions consisted of actinobacteria strain Streptomyces sp. SH-1312 with addition of mix metals (Co2+ + Zn2+) ions at 0.5 mM in Gause’s medium. Under these conditions, the stress metabolite anhydromevalonolactone (MVL) was produced, which was absent in the normal culture of strain and other metals combinations. Furthermore, the stress metabolite was also evaluated for its anti-oxidant and cytotoxic activities. The compound exhibited remarkable anti-oxidant activities, recording the IC50 value of 19.65 ± 5.7 µg/mL in DPPH, IC50 of 15.49 ± 4.8 against NO free radicals, the IC50 value of 19.65 ± 5.22 µg/mL against scavenging ability, and IC50 value of 19.38 ± 7.11 µg/mL for iron chelation capacity and the cytotoxic activities against PC3 cell lines were recorded with IC50 values of 35.81 ± 4.2 µg/mL after 24 h, 23.29 ± 3.8 µg/mL at 48 h, and 16.25 ± 6.5 µg/mL after 72 h. Further mechanistic studies have revealed that the compound MVL has shown its pharmacological efficacy by upregulation of P53 and BAX while downregulation of BCL-2 expression, indicating that MVL is following apoptosis in varying degrees. To better understand the pharmacological properties of MVL, in this work, the absorption, distribution, metabolism, excretion, and toxicity (ADMET) were also evaluated. During ADMET predictions, MVL has displayed a safer profile in case of hepatotoxicity, cytochrome inhibition and also displayed as non-cardiotoxic. The compound MVL showed good binding energy in the molecular docking studies, and the results revealed that MVL bind in the active region of the target protein of P53 and BAX. This work triumphantly announced a prodigious effect of heavy metals on actinobacteria with fringe benefits as a key tool of MVL production with a strong pharmacological and pharmacokinetic profile.

PGPR-Mediated Plant Growth Attributes and Metal Extraction Ability of Sesbania sesban L. in Industrially Contaminated Soils

The release of harmful wastes via different industrial activities is the main cause of heavy metal toxicity. The present study was conducted to assess the effects of heavy metal stress on the plant growth traits, antioxidant enzyme activities, chlorophyll content and proline content of Sesbania sesban with/without the inoculation of heavy-metal-tolerant Bacillus gibsonii and B. xiamenensis. Both PGP strains showed prominent ACC-deaminase, indole acetic acid, exopolysaccharides production and tolerance at different heavy metal concentrations (50–1000 mg/L). Further, in a pot experiment, S. sesban seeds were grown in contaminated and noncontaminated soils. After harvesting, plants were used for the further analysis of growth parameters. The experiment comprised of six different treatments. The effects of heavy metal stress and bacterial inoculation on the plant root length; shoot length; fresh and dry weight; photosynthetic pigments; proline content; antioxidant activity; and absorption of metals were observed at the end of the experiment. The results revealed that industrially contaminated soils distinctly reduced the growth of plants. However, both PGPR strains enhanced the root length up to 105% and 80%. The shoot length was increased by 133% and 75%, and the fresh weight was increased by 121% and 129%. The proline content and antioxidant enzymes posed dual effects on the plants growing in industrially contaminated soil, allowing them to cope with the metal stress, which enhanced the plant growth. The proline content was increased up to 190% and 179% by the inoculation of bacterial strains. Antioxidant enzymes, such as SOD, increased to about 216% and 245%, while POD increased up to 48% and 49%, respectively. The results clearly show that the utilized PGPR strains might be strong candidates to assist S. sesban growth under heavy metal stress conditions. We highly suggest these PGPR strains for further implementation in field experiments.

Mixotrophic bacteria for environmental detoxification of contaminated waste and wastewater.

Mixotrophic bacteria provide a desirable alternative to the use of classical heterotrophic or chemolithoautotrophic bacteria in environmental technology, particularly under limiting nutrients conditions. Their bi-modal ability of adapting to inorganic or organic carbon feed and sulfur, nitrogen, or even heavy metal stress conditions are attractive features to achieve efficient bacterial activity and favorable operation conditions for the environmental detoxification or remediation of contaminated waste and wastewater. This review provides an overview on the state of the art and summarizes the metabolic traits of the most promising and emerging non-model mixotrophic bacteria for the environmental detoxification of contaminated wastewater and waste containing excess amounts of limiting nutrients. Although mixotrophic bacteria usually function with low organic carbon sources, the unusual capabilities of mixotrophic electroactive exoelectrogens and electrotrophs in bioelectrochemical systems and in microbial electrosynthesis for accelerating simultaneous metabolism of inorganic or organic C and N, S or heavy metals are reviewed. The identification of the mixotrophic properties of electroactive bacteria and their capability to drive mono- or bidirectional electron transfer processes are highly exciting and promising aspects. These aspects provide an appealing potential for unearthing new mixotrophic exoelectrogens and electrotrophs, and thus inspire the next generation of microbial electrochemical technology and mixotrophic bacterial metabolic engineering. KEY POINTS: • Mixotrophic bacteria efficiently and simultaneously remove C and N, S or heavy metals. • Exoelectrogens and electrotrophs accelerate metabolism of C and N, S or heavy metals. • New mixotrophic exoelectrogens and electrotrophs should be discovered and exploited.

Hydroponic Phytoremediation of Ni, Co, and Pb by Iris Sibirica L.

Heavy metal pollution in mine wastelands is quite severe. Iris sibirica L., an emergent wetland plant, is characterized by an ability to survive under high stress of heavy metals. This study aimed to explore the phytoremediation ability of nickel (Ni), cobalt (Co), and lead (Pb) by Iris sibirica L. under hydroponic conditions. A series of tests were conducted at different metal stress conditions to evaluate the phytoextraction and tolerance of Iris sibirica L. The concentrations of Ni, Co, and Pb in plant shoots reached their highest values in 500 mg L−1 treatments, where they were 6.55%, 23.64%, and 79.24% higher than those in 300 mg L−1, respectively. The same concentrations in roots also reached their peak in 500 mg L−1 treatments, where they were 5.52%, 33.02%, and 70.15% higher than those in 300 mg L−1, respectively. Bioconcentration factors (BCF) for Ni, Co, and Pb revealed the phytoextraction ability of Iris sibirica L., and the translocation factors (TCF) showed that Ni may be most easily translocated in the plant, followed by Co and Pb. This study indicates that, compared with Ni and Co, Iris sibirica L. is more suitable for the phytoremediation of Pb-contaminated metal mine wastelands.

Exposure to NaCl enhances Cd2＋ biosorption potential of Sesuvium portulacastrum (L.)

Cadmium (Cd2＋) is a major heavy metal pollutant and it causes many serious effects on the environment. The established Cd2＋ removal methods are expensive and produce secondary waste, while biosorption is a potential alternative. In view of this, Sesuvium portulacastrum (L.) is explored, which is a facultative halophyte and is known to survive under both salt and heavy metal stress conditions. Using the dried powder of Sesuvium biomass, two independent biosorbents were prepared including ConB (grown under control condition) and NaClB (grown under 200 mM NaCl) and their Fourier-transform infrared spectroscopy (FTIR) indicated significant alteration in peak position of various functional groups. The Cd2＋ biosorption capacity in NaClB (306 mg g−1) was found higher than ConB (203 mg g−1). The kinetic and equilibrium studies revealed the contribution of intraparticle diffusion in the biosorption process of both the biosorbents. Further, the higher intraparticle diffusion rate constant indicated the faster biosorption process in NaClB. The experimental data correlated better with Freundlich equilibrium isotherm (r2=0.96 for ConB and r2=0.99 for NaClB) than Langmuir, indicating multilayer biosorption and heterogeneity within the biosorbents. Scanning electron microscope (SEM) imaging indicated that the rough surface of ConB changed to smooth after Cd2＋ biosorption, with lesser number of pores. In case of NaClB, Cd2＋ biosorption narrowed the vertical channels. EDX (Energy Dispersive X-ray) spectrum validated the Cd2＋ binding in both ConB and NaClB. Taken together, the study highlighted NaCl-treated Sesuvium as an eco-friendly green biosorbent for Cd2＋ removal from aqueous solutions.