Amaranthus Biochar-Based Microbial Cell Composites for Alleviation of Drought and Cadmium Stress: A Novel Bioremediation Approach

Metal contamination coupled with aridity is a major challenge for remediation of abiotic stressed soils throughout the world. Both biochar and beneficial bacteria showed a significant effect in bioremediation; however, their conjugate study needs more exploration. Two rhizobacteria strains Serratia sp. FV34b and Pseudomonas sp. ASe42b isolated from multi-metal and drought stressed sites showed multiple plant-growth-promoting attributes (phosphate solubilization, indole-3-acetic acid, siderophore, and ammonia production). Both strains were able to tolerate a high concentration of Cd along with being resistant to drought (-0.05 to -0.73 MPa). The seldom studied biomass of Amaranthus caudatus L. was used for biochar preparation by pyrolyzing it at 470 °C for 160 min under limited oxygen and then using it for the preparation of biochar-based microbial cell composites (BMC)s. To check the efficiency of BMC under Cd stress (21 mg kg-1 soil) and drought, a pot-scale study was conducted using Brassica napus L. for 47 days. Both the BMC5 (Biochar + Serratia sp. FV43b) and BMC9 (Biochar + Pseudomonas sp. ASe42b) improved the seed germination, plant biometrical (shoot and root biomass, length of organs) and physiological (photosynthetic pigments, proline, malondialdehyde, and relative water content) parameters under drought (exerted until it reaches up to 50% of field capacity) and Cd-spiked soil. However, for most of them, no or few significant differences were observed for BMC9 before and after drought. Moreover, BMC9 maximized the Cd accumulation in root and meager transfer to shoot, making it a best bioformulation for sustainable bioremediation of Cd and drought stressed soils using rapeseed plant.

Phytomitigation potential and adaptive responses of helophyte Typha latifolia L. to copper smelter-influenced heavily multi-metal contamination

The present study of phytomitigation potential and adaptive physiological and biochemical responses of helophyte Typha latifolia L. growing in water bodies at different distances from the century-old copper smelter (JSC "Karabashmed" Chelyabinsk Region, Russia) was conducted for the first time. This enterprise is one of the most dominant sources of multi-metal contamination for water and land ecosystems. The aim of the research was to assess the heavy metal (Cu, Ni, Zn, Pb, Cd, Mn, and Fe) accumulation, the photosynthetic pigment complex, and some redox reactions in T. latifolia from six differently technogenic impacted sites. In addition, the quantity of mesophilic aerobic and facultative anaerobic microorganisms (QMAFAnM) in rhizosphere sediments, as well as some plant growth-promoting (PGP) attributes of 50 isolates from each site, were determined. The water and sediment metal concentrations in highly contaminated sites exceeded the permissible/critical limits and were found much higher than that previously reported by other researchers while studying this helophyte. Both the degree of contamination and geoaccumulation indexes further elucidated extremely high contamination due to prolonged activity of copper smelter. T. latifolia accumulated significantly higher concentrations of the most of studied metals in its roost and rhizome with meager transfer to leaves (the translocation factors were less than one). Spearman's rank correlation coefficient showed a strong positive correlation between the metal concentration in sediments and its content in T. latifolia leaves (rs = 0.786 at p < 0.001 on average) and roots/rhizome (rs = 0.847 at p < 0.001 on average). In highly contaminated sites, the folia content of chlorophyll a and carotenoids decreased (by 30 and 38%, respectively), while lipid peroxidation enhanced (by 42%) on average compared to S1-S3 sites. These responses were accompanied by increasing non-enzymatic antioxidant content (soluble phenolic compounds, free proline, and soluble thiols) that allow plants to resist under significant anthropogenic loads. QMAFAnM in the five studied rhizosphere substrates varied insignificantly (2.5 × 106 - 3.8 × 107 cfu g-1 DW) and was decreased only in the most contaminated site (4.5 × 105). The proportion of rhizobacteria capable of fixing atmospheric nitrogen decreased by 1.7 times, solubilizing phosphates by 1.5 times, and synthesizing indol-3-acetic acid by 1.4 times in highly contaminated sites, while the amount of siderophore, 1-aminocyclopropane-1-carboxylate deaminase, and HCN producing bacteria did not considerably change. The results indicate high resistance of T. latifolia to prolonged technogenic impact, probably due to compensatory adaptive changes in the nonenzymatic antioxidant level and presence of beneficial microorganisms. Thus, T. latifolia was found to be a promising metal-tolerant helophyte that could help in mitigation of metal toxicity due to their phytostabilization even in heavily contaminated environment.

Biofertilizer Based on Biochar and Metal-Tolerant Plant Growth Promoting Rhizobacteria Alleviates Copper Impact on Morphophysiological Traits in Brassica napus L

Metal tolerant plant growth-promoting (PGP) rhizobacteria are promising for enhancing plant productivity under copper (Cu) stress. Present pot scale experiment was conducted on Brassica napus L. to check the efficiency of rhizobacteria isolated from the rhizosphere of Tussilago farfara L. growing on Cu-contaminated soils. Out of fifty Cu tolerant strains, three isolates which showed multiple PGP traits such as indole-3-acetic acid (IAA) synthesis, phosphate (PS) solubilization, siderophore and ammonia production were identified preliminarily by morphological and physiological characteristics followed by 16S rRNA gene sequencing. The best Bacillus altitudinis strain TF16a which showed IAA: 15.5 mg L-1, PS: 215 mg L-1, siderophore halo zone ratio of 3.0 with high ammonia production was selected to prepare a biochar-based biofertilizer (BF). Seedling test showed maximum growth of B. napus shoot and root in presence of 5% of BF and this concentration was selected for further experiment. The pot experiment included four treatments: control (soil), 100Cu (100 mg Cu kg-1 soil), 5%BF (v/v), and 5%BF+100Cu, which were carried out for 30 days, after which the morphological, physiological, and biochemical parameters of B. napus were studied. The Cu treatment caused its accumulation in shoot and root up to 16.9 and 30.4 mg kg-1 DW, respectively, and increased malondialdehyde (MDA) content by 20%. Application of BF with copper led to the decrease in the Cu accumulation by 20% for shoot and 28% for root while MDA content was the same as in the control. Both treatments of BF with and without Cu increased chlorophyll a and b content by 1.3 times on average as well as non-enzymatic antioxidants such as soluble phenolic compounds (1.3 times) and free proline (1.6 times). Moreover, BF + Cu led to the increase in the biomass of shoot and root by 30 and 60%, respectively, while there was no significant effect on the growth characteristics of plants after the addition of BF without Cu. The study elucidates that BF based on B.altitudinis strain TF16a and biochar can be a promising bioformulation which could increase rapeseed growth under the moderate Cu concentration in soil.

Synergistic effect of ACC deaminase producing Pseudomonas sp. TR15a and siderophore producing Bacillus aerophilus TR15c for enhanced growth and copper accumulation in Helianthus annuus L

Copper (Cu) is an essential element, however it's excess into the environment causes detrimental effect on plant and risks for public health. Four Cu and drought tolerant 1-aminocyclopropane-1-carboxylate (ACC) deaminase producing rhizobacteria were isolated from the roots of Trifolium repens L. growing on Cu smelter contaminated soils, characterized and identified based on 16S rRNA gene sequencing. A consortium of high ACC deaminase (53.74 μM α-ketobutyrate mg^-1 protein h^-1) producing bacteria Pseudomonas sp. strain TR15a + siderophore producing Bacillus aerophilus strain TR15c significantly (p < 0.05) produced better results for multiple-metal tolerance including Cu (1750 mg kg^-1), antibiotic resistance (ampicillin, kanamycin, chloramphenicol, penicillin, tetracycline, and streptomycin) and plant growth promoting attributes (phosphate solubilization: 315 mg L^-1, indole-3-acetic acid (IAA) production: 8 mg L^-1, ammonia and hydrogen cyanide production) as compared to individual isolates. Pot scale experiment (enriched with 100 mg Cu kg^-1) showed inoculation of Helianthus annuus seeds with consortium of TR15a + TR15c had significantly (p < 0.05) improved seed germination by 32%, total dry biomass by 64%, root Cu by 47% and shoot Cu by 75% as compared to uninoculated control whereas 0.2-7 fold higher results were observed for above stated parameters as compared to four individual isolates studied. The result suggests consortium of ACC deaminase producing Pseudomonas sp. TR15a and siderophore producing B. aerophilus TR15c could play a vital role in enhanced Cu uptake and improvement of biomass and may provide a better alternative for decontamination of Cu contaminated natural ecosystem than individual isolates.

Nickel and copper accumulation strategies in Odontarrhena obovata growing on copper smelter-influenced and non-influenced serpentine soils: a comparative field study

The present investigation is the first in situ comparative study for the identification of Ni and Cu accumulation strategies involved in Odontarrhena obovata (syn. Alyssum obovatum (C.A. Mey.) Turcz.) growing in Cu-rich smelter-influenced (CSI) and non-Cu-influenced (NCI) sites. The total and Na₂EDTA (disodium ethylenediaminetetraacetic acid)-extractable metal concentration in soils and plant tissues (roots, stem, leaves and flowers) were determined for CSI and NCI sites. High concentrations of total Ni, Cr, Co and Mg in the soil suggest serpentine nature of both the sites. In spite of high total and extractable Cu concentrations in CSI soil, majority of its accumulation was restricted to O. obovata roots showing its excluder response. Since the translocation and bioconcentration factors of Ni > 1 and the foliar Ni concentration > 1000 μg g^-1, it can be assumed that O. obovata has Ni hyperaccumulation potential for both the sites. No significant differences in chlorophyll content in O. obovata leaves were observed between studied sites, suggesting higher tolerance of this species under prolonged heavy metal stress. Furthermore, this species from CSI site demonstrated rather high viability under extreme technogenic conditions due to active formation of antioxidants such as ascorbate, free proline and protein thiols. The presence of Cu in higher concentration in serpentine soil does not exert detrimental effect on O. obovata and its Ni hyperaccumulation ability. Thus, O. obovata could act as a putative plant species for the remediation of Cu-rich/influenced serpentine soils without compromising its Ni content and vitality.

Bioaugmentation with copper tolerant endophyte Pseudomonas lurida strain EOO26 for improved plant growth and copper phytoremediation by Helianthus annuus

Organic fertilizers became a better alternative to chemical fertilizers in modern agricultural practices however, contamination of copper (Cu) from organic fertilizer is still a major concern for the globe. Plant growth promoting (PGP) microorganisms showed their efficiency to combat with this problem and thus Cu tolerant PGP endophytes from roots of Odontarrhena obovata (Alyssum obovatum) growing on Cu smelter contaminated serpentine soil were explored in present study. Out of twenty-four isolates, Pseudomonas lurida strain EOO26 identified by 16s rRNA gene sequencing was selected to check its efficacy for Cu-remediation. The strain EOO26 showed multi-metal tolerance, drought resistance and exhibited PGP attributes such as 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, siderophore and ammonia production. Significant production of indole-3-acetic acid and phosphate-solubilization under different Cu concentration (0-100 mg L^-1) at varying pH (5.0-8.0) suggests potentiality of this strain to work effectively under wide range of abiotic stress conditions. Plant growth experiment (pH 6.8 ± 0.3) in copper spiked soil suggested a significant increase in length and dry weight of root and shoot of sunflower (Helianthus annuus) after inoculation with strain EOO26. Plants inoculated with strain EOO26 resulted in increase in Cu uptake by 8.6-fold for roots and 1.9-fold for leaves than uninoculated plants. The total plant uptake in inoculated Cu treatment was 2.6-fold higher than uninoculated one, which is much higher than the previously reported Cu accumulating plants. The excellent adaptation abilities and promising metal removal efficiency strongly indicate superiority of strain EOO26 for phytoremediation of Cu-contamination and may work effectively for Cu removal from contaminated soils.

Toxic metal(loid)s contamination and potential human health risk assessment in the vicinity of century-old copper smelter, Karabash, Russia

Active smelters release high concentration of multiple toxic metal(loid)s into the environment, degrading the soil cover and posing high risks to human health. The present study investigates Cu along with other metal(loids) such as As, Cd, Hg, Co, Mn, Pb and Zn in the soil collected from the vicinity of Cu smelter, Karabash, Russia, and potential health risks to local children and adults were assessed. The average concentrations of Cu, Zn, Pb, As, Cd, and Hg in the exposed soil were 2698, 1050, 702, 392, 9 and 2 mg kg^-1, respectively, which was significantly (p < 0.05) much higher than reference soil: Cu(107), As(18), Cd(0.3), Hg(0.2), Pb(54) and Zn(125) mg kg^-1. The enrichment factor (EF) for Cu, Hg, Pb and Zn showed significant enrichment, whereas very high enrichment was recorded for As (20.0) and Cd (27.6) suggesting the soil was severely affected by smelting activities. The pollution load index was tenfold higher than the acceptable level of one, whereas potential ecological risk factor showed very high potential risks of Cd and Hg, along with a considerable ecological risk of As and Cu. Very high ecological risk index of 1810 indicates severe degradation of environmental ecosystem. The results of EF, Pearson correlation and principle component analysis were complementary and suggest the anthropogenic source of contamination for Cu, As, Pb, Hg and Cd. The present result suggests As > Pb > Cu in the exposed soil were the major contributors for the health risks and account for 81%, 12% and 5%, and 77%, 12% and 8% of hazard quotient for children and adults, respectively. Noticeably, the health risks to local children dwelling in the vicinity of Cu smelter were 12 and 20 times higher than to adult and the acceptable level of one, respectively. Therefore, in order to reduce the health risk due to metal(loid)s, mitigation measures are needed to remediate the pollution of the exposed soil.

Effect of the exogenous anthocyanin extract on key metabolic pathways and antioxidant status of Brazilian elodea (Egeria densa (Planch.) Casp.) exposed to cadmium and manganese

Present study deals with the effect of 24 h pre-incubation with exogenous anthocyanins (ANTH), extracted from red cabbage leaves, on key metabolic processes (photosynthesis and respiration) and pro-/antioxidant balance in the aquatic macrophyte Egeria densa (Planch.) Casp., Hydrocharitaceae family, treated with Cd and Mn (in sulfate form) at a concentration of 100 μmol. After five days of metal treatments, Cd was accumulated and the damage caused to metabolic processes was stronger than Mn. In Cd-treated leaves, the protein level, chlorophyll concentration and maximal photochemical efficiency of PS II decreased twofold, and net-photosynthesis was significantly inhibited, whereas lipid peroxidation and H₂O₂ production increased. In turn, protective responses developed, including an increase in the total soluble thiols, alternative respiratory pathway capacity and the activity of superoxide dismutase and peroxidases. Pre-incubation in the ANTH-enriched extract caused an increase in foliar ANTH content, enhanced Cd and reduced Mn uptake into the tissue. A decrease in the level of oxidative reactions, an increase in the protein and chlorophyll concentration compared to the control values and a partial improvement of the photosynthetic parameters confirmed the ability of ANTH to reduce Cd-induced damage effects and to mitigate ROS-driven stress reactions. Stimulation of catalase and ascorbate peroxidase activity, an alternative respiration capacity and non-enzymatic antioxidant (carotenoids, ascorbate and proline) synthesis by ANTH were also revealed. These data suggest that ANTH-enriched extract from red cabbage leaves has a protective action against metal toxicity in Egeria plants.

Urea increased nickel and copper accumulation in the leaves of Egeria densa (Planch.) Casp. and Ceratophyllum demersum L. during short-term exposure

In the present study, two fresh water plant species Egeria densa (Planch.) Casp. and Ceratophyllum demersum L. were subjected to separate and combined action of urea (2mМ) and metals (Ni and Cu, 10μM) to investigate the phytoremediation potential of these two submerged macrophytes during short-term experiments (48h). Both submerged macrophytes demonstrated high accumulative potential for Ni and Cu (average bioconcentration factors were 2505 for Ni and 3778 for Cu). The urea (2 mM) was not significantly toxic for studied plant species. Futhermore, urea worked as an additional source of nitrogen and stimulated some metabolic processes such as the synthesis of photosynthetic pigments, soluble proteins, non-enzymatic antioxidants, and activated some enzymes. Adding urea to the metals increased their accumulation in both macrophytes (on average by 35% for Ni and 15% for Cu). Combined action of urea and Ni did not have a significant effect on antioxidant response, but caused a sharp increase of urease activity (4 folds on an average) in both plants. The copper exerted a stronger toxic effect on both studied macrophytes compared to nickel. Adding urea to copper in some cases diminished the toxic action of this metal. Study concludes that the responses of E. densa and C. demersum to urea and metal action (separate and combined) were depended on the type of pollutant and the activity of antioxidant defence system. Therefore, the studied aquatic macrophytes found to be potential phytoremediators of water bodies, the addition of an organic nitrogen source in the form of urea in environmentally relevant concentration will increase the efficiency of phytoextraction of metals.

Thiols as biomarkers of heavy metal tolerance in the aquatic macrophytes of Middle Urals, Russia

Aquatic macrophytes, viz. Sagittaria sagittifolia L., Lemna gibba L., Elodea canadensis Michx., Batrachium trichophyllum (Chaix.) Bosch., Ceratophyllum demersum L. and Potamogeton sp. (P. perfoliatus L., P. alpinus Balb., P. crispus L., P. berchtoldii Fieber, P. friesii Rupr., P. pectinatus L.) were collected from 11 sites for determining their metal accumulation and thiols content. Cu(2+), Ni(2+), Mn(2+), Zn(2+), and Fe(3+) exceeded maximum permissible concentrations in chosen sites. Significant transfer of metals from water to leaves is observed in the order of Ni(2+) < Cu(2+) < Zn(2+) < Fe(3+) < Mn(2+). The maximum variation of bioconcentration factor was noticed for manganese. The accumulation of heavy metals in leaves was correlated with non-protein and protein thiols, confirming their important role in metal tolerance. The largest contribution was provided by Cu(2+) (on the average r = 0.88, p < 0.05), which obviously can be explained as an important role of these ions in thiols synthesis. Increased synthesis of thiols in the leaves allows the usage of SH-containing compounds as biomarkers of metal tolerance. Considering accumulation of metals and tolerance, B. trichophyllum, C. demersum and L. gibba are the most suitable species for phytoremediation of highly multimetal contamination, while E. canadensis and some species of Potamageton are suitable for moderately metal-polluted sites.

Urea-induced oxidative damage in Elodea densa leaves

Urea being a fertilizer is expected to be less toxic to plants. However, it was found that urea at 100 mg L(-1) caused the oxidative stress in Elodea leaves due to the formation of reactive oxygen species (ROS) and lipid peroxidation that are known to stimulate antioxidant pathway. Urea at a concentration of 500 and 1000 mg L(-1) decreased low-molecular-weight antioxidants. In this case, the antioxidant status of plants was supported by the activity of antioxidant enzymes such as superoxide dismutase and guaiacol peroxidase. A significant increase in the soluble proteins and -SH groups was observed with high concentrations of urea (30-60 % of control). Thus, the increased activity of antioxidant enzymes, low-molecular-weight antioxidants, and induced soluble protein thiols are implicated in plant resistance to oxidative stress imposed by urea. We found that guaiacol peroxidase plays an important role in the removal of the peroxide in Elodea leaves exposed to 1000 mg L(-1)of urea.

Ceratophyllum demersum L. and Potamogeton alpinus Balb. from Iset' river, Ural region, Russia differ in adaptive strategies to heavy metals exposure--a comparative study

We examined the uptake of five heavy metals (Cu, Fe, Ni, Zn, and Mn) in Ceratophyllum demersum L. (hornwort) and Potamogeton alpinus Balb. (pondweed) from Iset' river, Ural region, Russia. This study was conducted in a territory that is highly urbanized where the surface waters are contaminated by a wide spectrum of pollutants. The environmental situation in this territory drastically deteriorated due to anthropogenic activity. The water quality in most of the water bodies in the Ural region is rather poor. In a comparative study of C. demersum and P. alpinus, differential accumulation pattern was noted for heavy metals (HMs). Higher amounts of HMs accumulated in C. demersum compared to P. alpinus. Also it was shown that in leaves of C. demersum there were high amount of total phosphorus, nitrogen, organics acids and ash; high activity of guaiacol peroxidase; high content of nonenzymatic antioxidants viz., flavonoids, ascorbate, glutathione and proline; high amount of thiols (soluble and membrane bound) compared to P. alpinus.

Influence of exogenous urea on photosynthetic pigments, (14)CO 2 uptake, and urease activity in Elodea densa-environmental implications

This paper analyzes the effect of exogenous urea in increased concentration gradient (0, 100, 500 and 1,000 mg L(-1)) on photosynthetic pigments (measured spectrophotometrically), uptake of (14)CO2 (using radioisotope), and urease activity (by measuring ammonia with Nessler's reagent) in leaves of Elodea densa Planch. We have observed that low concentration of urea (100 mg L(-1)) stimulates the accumulation of photosynthetic pigments and intensifies photosynthesis in E. densa, whereas high concentration (1,000 mg L(-1)) suppresses these processes. Urease activity increased by approximately 2.7 and 8 fold when exogenous urea concentrations were 100 and 500 mg L(-1), respectively. However, exogenous urea in high concentration (1,000 mg L(-1)) decreased urease activity by 1.5 fold compared to the control. The necessity of mitigating urea and other nitrogen-containing compounds (NH3 from urea) in water bodies has been discussed with emphasis on the potential for phytoremediation of urea using common water weed viz. E. densa.

Copper toxicity in leaves of Elodea canadensis Michx

Elodea canadensis (Canadian waterweed) has an ability to accumulate and bioconcentrate heavy metals. In this work, selected cellular responses for Cu treatment were studied in leaves of E. canadensis. Short term experiments, i.e. 1 week exposure to 0.5, 1, 5, and 10 microM of Cu indicated that concentrations up to 10 microM Cu causes a pronounced accumulation of photosynthetic pigments, a drastic degradation of soluble proteins with molecular weight above 18 kDa and a rapid accumulation of polypeptides with molecular weight below 14 kDa. The connection of these observations with copper detoxification mechanisms in aquatic macrophytes are discussed.