Mercury Stress Research Articles

Induction of phytoextraction, phytoprotection and growth promotion activities in Lupinus albus under mercury abiotic stress conditions by Peribacillus frigoritolerans subsp., mercuritolerans subsp. nov.

Strain SAICEUPBMT was isolated from soils of Almadén (Ciudad Real, Spain), subjected to a high mercury concentration. SAICEUPBMT significantly increased aerial plant weight, aerial plant length and the development of secondary roots under mercury stress; increased twice the absorption of mercury by the plant, while favoring its development in terms of biomass. Similarly, plants inoculated with SAICEUPBMT and grown in soils contaminated with mercury, express a lower activity of antioxidant enzymes; catalase enzymes (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) for defense against ROS (reactive oxygen species). Whole genome analysis showed that ANI (95. 96 %), dDDH (72.9 %), AAI (93.3 %) and TETRA (0.99) values were on the thresholds established for differentiation a subspecies. The fatty acids analysis related the strain with the Peribacillus frigoritolerans species. And the synapomorphic analysis reveals a common ancestor with analysis related the strain with the Peribacillus frigoritolerans species. Results from genomic analysis together with differences in phenotypic features and chemotaxonomic analysis support the proposal of strain SAICEUPBMT as the type strain of a novel subspecies for which the name Peribacillus frigoritolerans subps. mercuritolerans sp. nov is proposed. The absence of virulence genes and transmissible resistance mechanisms reveals its safety for agronomic uses, under mercury stress conditions. The ability of Peribacillus frigoritolerans subsp. mercuritolerans subsp. nov to improve plant development was tested in a Lupinus albus model, demonstrating a great potential for plant phytoprotection against mercury stress.

The regulatory roles of a plant neurotransmitter, acetylcholine, on growth, PSII photochemistry and antioxidant systems in wheat exposed to cadmium and/or mercury stress

Heavy metals increase in nature due to anthropogenic activities and negatively impact the growth, progress, and efficiency of plants. Among the toxic metal pollutants that can cause dangerous effects when accumulated by plants, mercury (Hg) and cadmium (Cd) were investigated in this study. These metals typically inhibit important enzymes and halt their functioning, thereby adversely affecting the capability of plants to achieve photosynthesis, respiration, and produce quality crops. Acetylcholine (ACh) serves as a potent neurotransmitter present in both primitive and advanced plant species. Its significant involvement in diverse metabolic processes, particularly in regulating growth and adaptation to stress, needs to be further elucidated. For this aim, effects of acetylcholine (ACh1, 10 μM; ACh2, 100 μM) were survey in Triticum aestivum under Hg and/or Cd stress (Hg, 50 μM; Cd, 100 μM). Wheat seedlings exhibited a growth retardation of about 24% under Hg or Cd stress. Combined stress conditions (Cd + Hg) resulted in a decrease in RWC by approximately 16%. Two different doses of ACh treatment to stressed plants positively affected growth parameters and regulated the water relations. Gas exchange was limited in stress groups, and the photochemical quantum competency of PSII (Fv/Fm) was suppressed. Cd + ACh1 and Cd + ACh2 treatments resulted in approximately 2-fold and 1.5-fold improvement in stomatal conductance and carbon assimilation rate, respectively. Similarly, improvement was observed with ACh treatments in wheat seedlings under Hg stress. Under Cd and/or Hg stress, high levels of H2O2 accumulated and lipid peroxidation occurred. According to our results, ACh treatment upon Cd and Hg stresses improved the activities of SOD, POX, and APX, thereby reducing oxidative damage. In conclusion, ACh treatment was found to ensure stress tolerance and limit the adverse effects caused by heavy metals.

Reshaping the root endophytic microbiota in plants to combat mercury-induced stress

Emerging evidence suggests that plants experiencing abiotic stress actively seek help from soil microbes. However, the empirical evidence supporting this strategy is limited, especially in response to heavy metal stress. We used integrated microbial community profiling and culture-based methods to investigate the interaction between mercury (Hg) stress, the entophytic root microbiome, and maize seedlings. The results of the pot experiment showed that soil Hg (20 mg/kg) strongly inhibited maize growth, indicating its strong phytotoxicity. Furthermore, Hg stress significantly altered the structure of the bacterial and fungal communities and enriched the potentially pathogenic Fusarium sp., suggesting that soil Hg stress may enhance the bio-stress induced by Fusarium species in maize. Additionally, soil Hg also led to the enrichment of beneficial bacterial members of Streptomyces, Lysobacter, and Sphingomonas (defined as differential species), which were also identified as keystone species in the Hg treatment by the analysis of co-occurrence networks. Therefore, it can be postulated that the members of Streptomyces, Lysobacter, and Sphingomonas function as stress-alleviating microbes. We successfully isolated the representatives of these stress-alleviating microbes. As expected, these strains mitigated the detrimental effects of Hg stess for the maize seedlings, suggesting that plants recruit the stress-alleviated microbiota to combat Hg stress. This study provides insights into the potential of manipulating the root microbiome to enhance plant growth in polluted environments.

Dynamics of selenium-mercury interaction under mercury stress in high and low selenium rice genotypes

Recent studies have demonstrated that selenium (Se) reduces the accumulation of heavy metals in rice tissues. However, the interaction between Se and mercury (Hg) in rice genotypes with high Se content remains to be further investigated. In this study, we used high Se genotypes Z2057B and Z5097B and low Se genotype Yuenong to explore the dynamics of Se and Hg in various tissues. The results showed that high Se genotypes, coupled with low concentrations of exogenously applied Se, significantly reduced the uptake of Hg in rice plants. The findings indicated the following order of Hg accumulation: Roots> third leaf > second leaf > first leaf > stem > grains. Observations revealed that both high Se genotypes and Se supplementation significantly restricted the majority of Hg concentration in roots and minimized its translocation to the aerial parts of the rice plant. In high Se genotypes subjected to mercury stress, MDA accumulation was significantly reduced, and SOD antioxidant activity was enhanced in stem and leaves at jointing, booting, heading, and maturity stages as compared to low Se genotypes. The application of 1.0 mg of Se per kg soil significantly improved the agronomic and physiological characteristics, reduced the Hg contents in aerial parts, and increased the Se contents in polished rice grains. Hence, the results lead to the conclusion that (i) cultivating high Se rice genotypes is a viable approach to decrease the Hg accumulation in rice grains and serves as a crucial strategy to fulfill daily Se requirements, particularly for populations suffering from Se deficiency (ii) supplementing ordinary rice with 1–3 mg kg−1 of Se can effectively reduce Hg accumulation and improve the quality of the grains.

Diverse fates of ancient horizontal gene transfers in extremophilic red algae.

Horizontal genetic transfer (HGT) is a common phenomenon in eukaryotic genomes. However, the mechanisms by which HGT-derived genes persist and integrate into other pathways remain unclear. This topic is of significant interest because, over time, the stressors that initially favoured the fixation of HGT may diminish or disappear. Despite this, the foreign genes may continue to exist if they become part of a broader stress response or other pathways. The conventional model suggests that the acquisition of HGT equates to adaptation. However, this model may evolve into more complex interactions between gene products, a concept we refer to as the 'Integrated HGT Model' (IHM). To explore this concept further, we studied specialized HGT-derived genes that encode heavy metal detoxification functions. The recruitment of these genes into other pathways could provide clear examples of IHM. In our study, we exposed two anciently diverged species of polyextremophilic red algae from the Galdieria genus to arsenic and mercury stress in laboratory cultures. We then analysed the transcriptome data using differential and coexpression analysis. Our findings revealed that mercury detoxification follows a 'one gene-one function' model, resulting in an indivisible response. In contrast, the arsH gene in the arsenite response pathway demonstrated a complex pattern of duplication, divergence and potential neofunctionalization, consistent with the IHM. Our research sheds light on the fate and integration of ancient HGTs, providing a novel perspective on the ecology of extremophiles.

Effects of sulfur nanoparticles on rhizosphere microbial community changes in oilseed rape plantation soil under mercury stress

In the present study, experiments were conducted to assess the influence of nanoscale sulfur in the microbial community structure of metallophytes in Hg-contaminated rhizosphere soil for planting rapeseed. The results showed that the richness and diversity of the rhizobacteria community decreased significantly under Hg stress, but increased slightly after SNPs addition, with a reduction in the loss of Hg-sensitive microorganisms. Moreover, all changes in the relative abundances of the top ten phyla influenced by Hg treatment were reverted when subjected to Hg + SNPs treatment, except for Myxococcota and Bacteroidota. Similarly, the top five genera, whose relative abundance decreased the most under Hg alone compared to CK, increased by 19.05%–54.66% under Hg + SNPs treatment compared with Hg alone. Furthermore, the relative abundance of Sphingomonas, as one of the dominant genera for both CK and Hg + SNPs treatment, was actively correlated with plant growth. Rhizobacteria, like Pedobacter and Massilia, were significantly decreased under Hg + SNPs and were positively linked to Hg accumulation in plants. This study suggested that SNPs could create a healthier soil microecological environment by reversing the effect of Hg on the relative abundance of microorganisms, thereby assisting microorganisms to remediate heavy metal-contaminated soil and reduce the stress of heavy metals on plants.

Emergence of Highly Mercury Tolerant Plant Growth promoting Bacteria in Tea Plantation Soil of Darjeeling Hills

This study characterizes three strains of Gram-negative bacteria MTD10B, MTD10C and MTD10D isolated from soil collected from tea plantations of Darjeeling hills, exhibiting extreme tolerance towards mercury. The minimum inhibitory concentration of mercury against these strains sits at a high level of 0.2 mg/mL of HgCl2. The isolates also display an expansive pattern of resistance to known clinically relevant synthetic antibiotics and a host of other potent heavy metals such as lead, cadmium, arsenic, chromium, silver, nickel etc. Biochemical and molecular characterization via 16S rRNA sequencing identified MTD10B and MTD10C as strains of Brevundimonas diminuta and MTD10D as Alcaligenes faecalis respectively. This study also explores the plant growth promoting abilities of these strains and their respective growth trends under normal conditions in comparison to when they are under mercury stress. This work attempts to cultivate an understanding of their potential for use as candidates for the bioremediation of mercury contamination in diverse environments.

Mercury removal by Aquarius palifolius (Nees & Mart.) Christenh. & Byng: Isotherms model, superoxide dismutase activity, and chlorophyll content

Mercury is one of the heavy metals that became a global threat in this industrialization era. Artisanal and Small-Scale Gold Mining activities are the leading cause of this mercury pollution. Sustainable and environmentally friendly methods can be a solution to overcome this problem. Bioremediation methods use plants with defense mechanisms against mercury, namely Mexican sword plants or Aquarius palifolius, which is a promising solution. This research aimed to analyze the isotherm model of mercury content in A. palifolius in the Free Water Surface-Constructed Wetland (FWS-CW) reactor using the Langmuir and Freundlich isotherm equations; analyzed the activity of antioxidant enzymes in A. palifolius such as Superoxide dismutase (SOD); and also analyzed the effect of mercury stress on chlorophyll levels in A. palifolius. This research shows that the mercury phytoremediation process by A. palifolius is more suitable with the Langmuir isotherm model. There are no significant differences in SOD activity and chlorophyll levels between A. palifolius with and without mercury concentration. This indicates that A. palifolius is a hyperaccumulator plant that can survive in mercury stress conditions and even remove mercury from contaminated water.

The study on the effect of mercury pollution on soil microorganisms around mercury mining area

In order to further explore the effects of soil mercury pollution on soil microbial diversity and community structure, soil samples were randomly collected from 2 m, 20 m, 30 m, 500 m and 650 m periphery of Wanshan mining area, as 5 different treatments. Each treatment had 4 replicates. Soil microbial DNA was extracted from 20 soil samples, and then high-throughput sequencing technology was used to analyse the structure and distribution of bacterial and fungal communities. The results showed that the number of bacterial and fungal communities in T0–T30 treatments was significantly larger than that in T500–T650 treatments at order, family and genus level. Whatever, the number of uniquely distributed bacterial and fungal communities among 4 replicates soil samples was quite different at order, family and genus level. The results of the effect on the microbial community structure showed that there were both the same dominant bacterial and fungal communities, and the different dominant bacterial and fungal communities at any classification level, moreover, the number of same dominant bacterial and fungal communities was larger than that of different dominant bacterial and fungal communities. The results of relationship between soil environment factors and bacterial and fungal community structure showed that distance (Hg2+), EC and pH had a high correlation with community structure, especially the distance factor, that is, the content of mercury in soil had the highest effects on community structure. The internal heterogeneity of soil caused significant differences in bacterial and fungal community structure, and the emergence of dominant bacterial and fungal communities was a manifestation of better adaptability to long-term mercury stress and other stresses in soil, which will provide a scientific reference for further exploring the mechanism of mercury enrichment between microorganisms and plants.

Stochastic community assembly of abundant taxa maintains the relationship of soil biodiversity-multifunctionality under mercury stress

Stochastic community assembly of abundant taxa maintains the relationship of soil biodiversity-multifunctionality under mercury stress

Microbe-Mediated Impact on Cell Membrane Stability and Leaf Pigmentation in Pearl Millet under Toxic Mercury Stress in Soil

Pearl millet, Pennisetum glacum treated with Mycorrhiza, Rhizobium, and Trichoderma microbes, could grow in highly contaminated mercury soil. Microbe-mediated tolerance of this plant and the mechanism involved was studied after growing pearl millet in 100 ppm of mercury-contaminated soil for 120 days. The different parameters analyzed were associated with photosynthesis and the stability of the cell membrane. Mercury contamination led to the inhibition of growth in the leaves and reduced photosynthesis and membrane stability. The defensive mechanism of P. glacum under mercury stress was aided by Mycorrhiza, Rhizobium, and Trichoderma and Hg-related toxicity in the soil was averted. Photosynthetic parameters such as chlorophyll a b, carotenoids, and anthocyanin were quantified. The stability and injury of the cell membrane were measured. The results showed a significant role of microbes in improving the tolerance of P. glacum against metal stress in the soil.. KEYWORDS :Antioxidants, Chlorophyll, Mycorrhiza, Pearl millet, Trichoderma, Rhizobium

Insights into the reduction of methylmercury accumulation in rice grains through biochar application: Hg transformation, isotope fractionation, and transcriptomic analysis

Methylmercury (MeHg), a potent neurotoxin, easily moves from the soil into rice plants and subsequently accumulates within the grains. Although biochar can reduce MeHg accumulation in rice grains, the precise mechanism underlying biochar-mediated responses to mercury (Hg) stress, specifically regarding MeHg accumulation in rice, remains poorly understood. In the current study, we employed a 4% biochar amendment to remediate Hg-contaminated paddy soil, elucidate the impacts of biochar on MeHg accumulation through a comprehensive analysis involving Hg isotopic fractionation and transcriptomic analyses. The results demonstrated that biochar effectively lowered the levels of MeHg in paddy soils by decreasing bioavailable Hg and microbial Hg methylation. Furthermore, biochar reduced the uptake and translocation of MeHg in rice plants, ultimately leading to a reduction MeHg accumulation in rice grains. During the process of total mercury (THg) uptake, biochar induced a more pronounced negative isotope fractionation magnitude, whereas the effect was less pronounced during the upward transport of THg. Conversely, biochar caused a more pronounced positive isotope fractionation magnitude during the upward transport of MeHg. Transcriptomics analyses revealed that biochar altered the expression levels of genes associated with the metabolism of cysteine, glutathione, and metallothionein, cell wall biogenesis, and transport, which possibly enhance the sequestration of MeHg in rice roots. These findings provide novel insights into the effects of biochar application on Hg transformation and transport, highlighting its role in mitigating MeHg accumulation in rice.

DNA hypomethylation-associated transcriptional rewiring enables resistance to heavy metal mercury (Hg) stress in rice

Mercury (Hg) is an important hazardous pollutant that can cause phytotoxicity and harm human health through the food chain. Recently, rice (Oryza sativa L.) has been confirmed as a potential Hg bioaccumulator. Although the genetic and molecular mechanisms involved in heavy metal absorption and translocation in rice have been investigated for several heavy metals, Hg is largely neglected. Here, we analyzed one Hg-resistant line in rice (RHg) derived from a DNA methyltransferase-coding gene, OsMET1–2 heterozygous mutant. Compared with its isogenic wild-type (WT), RHg exhibited a significantly higher survival rate after Hg treatment, ameliorated oxidative damage, and lower Hg uptake and translocation. RNAseq-based comparative transcriptomic analysis identified 34 potential Hg resistance-related genes involved in phytohormone signaling, abiotic stress response, and zinc (Zn) transport. Importantly, the elevated expression of Hg resistance-related genes in RHg was highly correlated with DNA hypomethylation in their putative promoter regions. An ionomic analysis unraveled a negative correlation between Zn and Hg in roots. Moreover, Hg concentration was effectively decreased by exogenous application of Zn in Hg-stressed rice plants. Our findings indicate an epigenetic basis of Hg resistance and reveal an antagonistic relationship between Hg and Zn, providing new hints towards Hg detoxification in plants. Environmental implicationMercury (Hg) as an important hazardous pollutant adversely impacts the environment and jeopardizes human health, due to its chronicity, transferability, persistence, bioaccumulation and toxicity. In this paper, we identified 34 potential genes that may significantly contribute to Hg resistance in rice. We find the expression of Hg resistance-related genes was highly correlated with DNA hypomethylation in their putative promoter regions. Our results also revealed an antagonistic relationship between Hg and Zinc (Zn), providing new hints towards Hg detoxification in plants. Together, findings of this study extend our current understanding of Hg tolerance in rice and are informative to breed seed non–accumulating rice cultivars.

Responses of the structure and function of microbes in Yellow River Estuary sediments to different levels of mercury

The health and stability of the estuary of the Yellow River ecosystem have come under increasing pressure from land-based inputs of heavy metals. While it is known that heavy metals affect the function and health of the microbial community, there remains little knowledge on the responses of the microbial community to heavy metals, particularly highly toxic mercury. The research aimed to characterize the responses of the sediment microbial community of the estuary of the Yellow River to different levels of mercury stress. Estuary sediment samples were collected for microbial community analysis, measurement of mercury [including total mercury (THg) and methylmercury (MeHg)], and measurement of other physicochemical factors, including pH, total organic carbon (TOC), sulfide, iron ratio (Fe3+/Fe2+), ammonium salt (NH4+), and biochemical oxygen demand (BOD). The application of 16S rRNA sequencing identified 60 phyla of bacteria, dominated by Proteobacteria, Firmicutes, and Bacteroidetes. Stations with higher THg or MeHg and lower microbial abundance and diversity were generally distributed further outside of the estuary. Besides mercury, the measured physicochemical factors had impacts on microbial diversities and distribution. Metagenomics assessment of three stations, representative of low, moderate, and high mercury concentrations and measured physicochemical factors, revealed the abundances and functions of predicted genes. The most abundant genes regulating the metabolic pathways were categorized as metabolic, environmental information processing, and genetic information processing, genes. At stations with high levels of mercury, the dominant genes were related to energy metabolism, signal transport, and membrane transport. Functional genes with a mercury-resistance function were generally in the mer system (merA, merC, merT, merR), alkylmercury lyase, and metal-transporting ATPase. These results offer insight into the microbial community structure of the sediments in the Yellow River Estuary and the microbial function of mercury resistance under mercury stress.

Soil core microbiota drive community resistance to mercury stress and maintain functional stability

Soil microbial communities have resistance to environmental stresses and thus can maintain ecosystem functions such as decomposition, nutrient provisioning, and plant pathogen control. However, predominant factors driving community resistance of soil microbiome to heavy metal pollution stresses and ecosystem functional stability are still unclear, limiting our ability to forecast how soil pollution might affect ecosystem sustainability. Here, we conducted microcosm experiments to estimate the importance of soil microbiome in predicting community resistance to heavy metal mercury (Hg) stress in paired paddy and upland fields. We found that community resistance of soil microbiome was strongly correlated with ecosystem functional stability, so were the individual groups of organisms such as bacteria, saprotrophic fungi, and phototrophic protists. The core phylotypes within soil microbiome had a major contribution to community resistance, which was essential for the maintenance of functional stability. Co-occurrence network further confirmed that community resistances of main ecological clusters were positively correlated with ecosystem functional stability. Together, our results provide new insights into the link between community resistance and functional stability, and highlight the importance of core microbiota in driving community resistance to environmental stresses and maintain functional stability.

Effect of Mercury Stress on the Growth and Lipid Content of Euglena sp. and Echinodorus palaefolius

One way to reduce the adverse effects of the heavy metals mercury in the aquatic environment are using organisms to break down or convert toxic substances into non-toxic forms, either by phytore- mediation or phycoremediation. This research aimed to analyze the growth and lipid content of Euglena sp. after mercury exposure. This research also aimed to analyze the growth of E. palaefolius which is associated with Euglena sp. In this study, the bioremediation ability of Euglena sp. and Echinodorus palaefolius through treatment with mercury concentrations of 5 ppm, 10 ppm, 15 ppm, and 20 ppm, as well as association and non-association treatments. The parameters are the growth of Euglena sp. and the association between Euglena sp. andE. palaefolius measurement and lipid content. The result of the growth of Euglena sp. experienced a significant increase. Lipid content in Euglena sp. was also seen high at 10 ppm mercury concentration. In E. palaefolius, the ability to adsorb heavy metals was also shown by the large diameter of the stems and also the plant growth which has optimal growth in the treatment of 10 ppm mercury stress.

Water deficit aggravated the inhibition of photosynthetic performance of maize under mercury stress but is alleviated by brassinosteroids.

Mercury (Hg) significantly inhibits maize (Zea mays L.) production, which could be aggravated by water deficit (WD) due to climate change. However, there is no report on the maize in response to combined their stresses. This work was conducted for assessing the response and adaptive mechanism of maize to combined Hg and WD stress using two maize cultivars, Xianyu (XY) 335 and Yudan (YD) 132. The analysis was based on plant growth, physiological function, and transcriptomic data. Compared with the single Hg stress, Hg accumulation in whole plant and translocation factor (TF) under Hg+WD were increased by 64.51% (1.44mgkg-1) and 260.00%, respectively, for XY 335; and 50.32% (0.62mgkg-1) and 220.02%, respectively, for YD 132. Combined Hg and WD stress further increased the reactive oxygen species accumulation, aggravated the damage of the thylakoid membrane, and decreased chlorophyll content compared with single stress. For example, Chl a and Chl b contents of XY 335 were significantly decreased by 48.67% and 28.08%, respectively at 48h after Hg+WD treatment compared with Hg stress. Furthermore, transcriptome analysis revealed that most of down-regulated genes were enriched in photosynthetic-antenna proteins, photosynthesis, chlorophyll and porphyrin metabolism pathways (PsbS1, PSBQ1 and FDX1 etc.) under combined stress, reducing light energy capture and electron transport. However, most genes related to the brassinosteroids (BRs) signaling pathway were up-regulated under Hg+WD stress. Correspondingly, exogenous BRs significantly enhanced the maize tolerance to stress by decreasing Hg accumulation and TF, and raising activities of antioxidant enzyme, the content of chlorophyll and photosynthetic performance. The PI, Fv/Fm and Fv/Fo of Hg+WD+BR treatment were increased by 29.88%, 32.06%, and 14.56%, respectively, for XY 335 compared to Hg+WD. Overall, combined Hg and WD stress decreased photosynthetic efficiency by adversely affecting light absorption and electron transport, especially in stress-sensitive variety, but BRs could alleviate the inhibition of photosynthesis, providing a novel strategy for enhancing crop Hg and WD tolerance and food safety.

Oxidative stress protection and growth promotion activity of Pseudomonas mercuritolerans sp. nov., in forage plants under mercury abiotic stress conditions.

SAICEUPSMT strain was isolated from soils in the mining district of Almadén (Ciudad Real, Spain), subjected to a high concentration of mercury. Using the plant model of lupinus, the strain was inoculated into the rhizosphere of the plant in a soil characterized by a high concentration of mercury (1,710 ppm) from an abandoned dump in the mining district of Almadén (Ciudad Real, Spain). As a control, a soil with a minimum natural concentration of mercury, from a surrounding area, was used. Under greenhouse conditions, the effect that the inoculum of the SAICEUPSMT strain had on the antioxidant capacity of the plant was studied, through the quantification of the enzymatic activity catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and glutathione reductase (GR). Likewise, the capacity of the plant to bioaccumulate mercury in the presence of the inoculum was studied, as well as the effect on the biometric parameters total weight (g), shoot weight (g), root weight (g), shoot length (cm), root length (cm), total number of leaves (N), and total number of secondary roots (No). Finally, in view of the results, the SAICEUPSMT strain was identified from the phenotypic and genotypic point of view (housekeeping genes and complete genome sequencing). The inoculum with the SAICEUPSMT strain in the presence of mercury produced a significant reduction in the enzymatic response to oxidative stress (CAT, APX, and SOD). It can be considered that the strain exerts a phytoprotective effect on the plant. This led to a significant increase in the biometric parameters total plant weight, root weight and the number of leaves under mercury stress, compared to the control without abiotic stress. When analyzing the mercury content of the plant with and without bacterial inoculum, it was found that the incorporation of the SAICEUPSMT strain significantly reduced the uptake of mercury by the plant, while favoring its development in terms of biomass. Given the positive impact of the SAICEUPSMT strain on the integral development of the plant, it was identified, proving to be a Gram negative bacillus, in vitro producer of siderophores, auxins and molecules that inhibit stress precursors. The most represented fatty acids were C16:0 (33.29%), characteristic aggregate 3 (22.80%) comprising C16:1 ω7c and C16: 1ω6c, characteristic aggregate 8 (13.66%) comprising C18:1 ω7c, and C18: 1 cycle ω6c and C 17:0 (11.42%). From the genotypic point of view, the initial identification of the strain based on the 16S rRNA gene sequence classified it as Pseudomonas iranensis. However, genome-wide analysis showed that average nucleotide identity (ANI, 95.47%), DNA-DNA in silico hybridization (dDDH, 61.9%), average amino acid identity (AAI, 97.13%), TETRA (0.99%) and intergenic distance (0.04) values were below the established thresholds for differentiation. The results of the genomic analysis together with the differences in the phenotypic characteristics and the phylogenetic and chemotaxonomic analysis support the proposal of the SAICEUPSMT strain as the type strain of a new species for which the name Pseudomonas mercuritolerans sp. is proposed. No virulence genes or transmissible resistance mechanisms have been identified, which reveals its safety for agronomic uses, under mercury stress conditions.

Unraveling the potential of bacteria isolated from the equatorial region of Indian Ocean in mercury detoxification

The marine environment is most vital and flexible with continual variations in salinity, temperature, and pressure. As a result, bacteria living in such an environment maintain the adaption mechanisms that are inherent in unstable environmental conditions. The harboring of metal-resistant genes in marine bacteria contributes to their effectiveness in metal remediation relative to their terrestrial counterparts. A total of four mercury-resistant bacteria (MRB) i.e. NIOT-EQR_J7 (Alcanivorax xenomutans); NIOT-EQR_J248 and NIOT-EQR_J251 (Halomonas sp.); and NIOT-EQR_J258 (Marinobacter hydrocarbonoclasticus) were isolated from the equatorial region of the Indian Ocean (ERIO) and identified by analyzing the 16S rDNA sequence. The MRBs can reduce up to 70% of Hg(II). The mercuric reductase (merA) gene was amplified and the mercury (Hg) volatilization was confirmed by the X-ray film method. The outcomes obtained from ICP-MS validated that the Halomonas sp. NIOT-EQR_J251 was more proficient in removing the Hg from culture media than other isolates. Fourier transform infrared (FT-IR) spectroscopy results revealed alteration in several functional groups attributing to the Hg tolerance and reduction. The Gas Chromatography-Mass Spectrometry (GC-MS) analysis confirmed that strain Halomonas sp. (NIOT-EQR_J248 and NIOT-EQR_J251) released Isooctyl thioglycolate (IOTG) compound under mercury stress. The molecular docking results suggested that IOTG can efficiently bind with the glutathione S-transferase (GST) enzyme. A pathway has been hypothesized based on the GC-MS metabolic profile and molecular docking results, suggesting that the compound IOTG may mediate mercuric reduction via merA-GST related detoxification pathway.

Mercury adsorption and reduction by nonlinear optical material (NLOM) DMABR loaded on Sepiolite: A mechanism study

Adsorption and reduction techniques are the main approaches for Hg2+ remediation. The delocalized electrons of nonlinear optical materials (NLOM) can be used as electron donors, while reduction remediation material based on this has not yet been reported. In this work, nonlinear optical materials (NLOM) DMABR loaded on sepiolite (SD material) was successfully synthesized via one-step hydrothermal treatment. The results of FTIR, SEM and UV–vis spectra suggested that the load material (SD) was well functionalized. Removal (adsorption and reduction) kinetics illustrated remediation potential of SD for Hg2+. Hg2+ can be effectively removed by the developed materials, with a capacity up to 68.5 mg/g. The high tolerance capacity of SD against interfering ions and organic species makes it appropriate for selective and efficient removal of Hg2+ from aqueous solutions. Characterized by XRD, Raman spectroscopy, XPS spectra, Zeta potential and elemental analyzer, the removal mechanism was elucidated. Under mercury stress, Sn2- in SD was decomposed into S22- and the coordination number with N increased, resulting in formation of α-HgS and inversion asymmetric products. It was proved that the reduction sites were at the strong chelate groups (N and S) due to the high content of oxidized states in spent samples. By adding mercury stepwise, the kinetics mechanism could be readily inferred by the changing emission intensity at 564 nm, providing a simpler way to study the kinetics of adsorption of contaminants using fluorescent materials. Taken together, our work showed that NLOM can participate in the redox electron transport chain of pollutants such as mercury, and thus offers promising potential for application in remediation of mercury contamination.