No abstract

Heavy metals (HMs) are toxic elements which contaminate the water bodies in developing countries because of their excessive discharge from industrial zones. Rice (Oryza sativa L) crops are submerged for a longer period of time in water, so irrigation with HMs polluted water possesses toxic effects on plant growth. This study was initiated to observe the synergistic effect of bacteria (Bacillus cereus and Lysinibacillus macroides) and zinc oxide nanoparticles (ZnO NPs) (5, 10, 15, 20 and 25 mg/L) on the rice that were grown in HMs contaminated water. Current findings have revealed that bacteria, along with ZnO NPs at lower concentration, showed maximum removal of HMs from polluted water at pH 8 (90 min) as compared with higher concentrations. Seeds primed with bacteria grown in HM polluted water containing ZnO NPs (5 mg/L) showed reduced uptake of HMs in root, shoot and leaf, thus resulting in increased plant growth. Furthermore, their combined effects also reduced the bioaccumulation index and metallothionine (MTs) content and enhanced the tolerance index of plants. This study suggested that synergistic treatment of bacteria with lower concentrations of ZnO NPs helped plants to reduce heavy metal toxicity, especially Pb and Cu, and enhanced plant growth.

Arsenic (As) contamination has emerged as a serious public health concern worldwide because of its accumulation and mobility through the food chain. Therefore, the current study was planned to check the effect of Bacillus subtilis-synthesized iron oxide nano particles (Fe3O4 NP) on rice (Oryza Sativa L.) growth against arsenic stress (0, 5, 10 and 15 ppm). Iron oxide nanoparticles were extracellular synthesized from Bacillus subtilis with a desired shape and size. The formations of nanoparticles were differentiated through UV-Visible Spectroscopy, FTIR, XRD and SEM. The UV-Visible spectroscopy of Bacillus subtilis-synthesized nanoparticles showed that the iron oxide surface plasmon band occurs at 268 nm. FTIR results revealed that different functional groups (aldehyde, alkene, alcohol and phenol) were present on the surface of nanoparticles. The SEM image showed that particles were spherical in shape with an average size of 67.28 nm. Arsenic toxicity was observed in seed germination and young seedling stage. The arsenic application significantly reduced seed germination (35%), root and shoots length (1.25 and 2.00 cm), shoot/root ratio (0.289), fresh root and shoots weight (0.205 and 0.260 g), dry root and shoots weight (6.55 and 6.75 g), dry matter percentage of shoot (12.67) and root (14.91) as compared to control. Bacillus subtilis-synthesized Fe3O4 NPs treatments (5 ppm) remarkably increased the germination (65%), root and shoot length (2 and 3.45 cm), shoot/root ratio (1.24) fresh root and shoot weight (0.335 and 0.275 mg), dry root and shoot weight (11.75 and 10.6 mg) and dry matter percentage of shoot (10.40) and root (18.37). Results revealed that the application of Fe3O4 NPs alleviated the arsenic stress and enhanced the plant growth. This study suggests that Bacillus subtilus-synthesized iron oxide nanoparticles can be used as nano-adsorbents in reducing arsenic toxicity in rice plants.

Nowadays, public concerns regarding deleterious effect of lead (Pb) is on rise due to its abundance and toxic effect on plants and other living organisms. In plants, it has no noticeable biological importance but can cause various morphological, physiological, and biochemical malfunctions. To evaluate the remediating potential of plant-derived smoke (Cymbopogon jwarancusa), a pot culture experiment was designed to investigate the physiological, biochemical, metabolic, and antioxidant parameters of roots in lead (0 (control), 500, 1000, and 1500 ppm)-contaminated soil. Under dark condition, seeds were primed in smoke solution with two dilutions (1:500 and 1:1000) for 24 h. With an increasing concentration of Pb stress, fresh and dry weight and total nitrogen and protein contents decreased significantly while an increase was observed in smoke-treated seed. With increasing Pb stress level, metabolites (i.e., proline, total soluble sugar, total soluble protein, glycine betaine), and antioxidants (i.e., superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, malonyldialdehyde, and HO), contents of roots were increased in non-treated (without smoke treatment) samples, whereas comparatively, a low level of alteration in aforementioned metabolites and antioxidative parameters was observed in the seeds treated with smoke solution. These results suggest a positive role of smoke in alleviating lead-induced changes in roots of two cultivated cultivars of rice grown in Pb-contaminated soil.

Nanoparticles and bacteria have received a great attention worldwide due to their ability to remove heavy metals (HMs) from wastewater. The current study is aimed at finding the interaction of HMs-resistance strains (Bacillus cereus and Lysinibacillus macroides) with different concentrations (5, 10, 15, 20, and 25 mg/L) of zinc oxide nanoparticles (ZnO NPs) and how they would cope with HM stress (Pb, Cd, Cr, and Cu). The growth rate and tolerance potential of bacteria were increased at lowered concentrations (5 and 10 mg/L) of ZnO NPs against HMs while it was unaffected at higher concentrations of ZnO NPs. These findings were confirmed by minimum inhibition zone and higher zinc solubilization at lower concentrations of ZnO NPs. Scanning electron microscopy (SEM) revealed that higher concentrations of ZnO NP increased HM accumulation in bacteria cells which had a significant impact on bacterial morphology and caused pores in bacterial membrane while in the case of lower concentrations, the cell remained unaffected. These results were further supported by the less production of antioxidant enzymes (SOD, POD, and CAT), thiobarbituric acid reactive substances (TBARS), and hydrogen peroxide (H2O2) contents at lower concentrations of ZnO NPs against heavy metal stress. This study suggested that synergistic treatment of Bacillus spp. with lower concentrations of ZnO NPs enhances the tolerance potential and significantly reduces the HM toxicity.