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30Heavy metals such as cobalt, copper, manganese, molybdenum, and zinc are essential in trace 31 amounts for growth by plants and other living organisms. However, in excessive amounts these 32 heavy metals have deleterious effects. Like other organisms, plants possess a variety of 33 detoxification mechanisms to counter the harmful effects of heavy metals. These include, the 34 restriction of heavy metals by mycorrhizal association, binding with plant cell wall and root 35 excretions, metal efflux from the plasma membrane, metal chelation by phytochelatins and 36 metallothioneins, and compartmentalization within the vacuole. Phytoremediation is an emerging 37 technology which uses plants and their associated rhizospheric microorganisms to remove 38 pollutants from contaminated sites. This technology is inexpensive, efficient and ecofriendly. 39 This review focuses on potential cellular and molecular adaptations by plants that are necessary 40 to tolerate heavy metal stress.41 42

ABSTRACT

The bacterium MNU16 was isolated from contaminated soils of coal mine and subsequently screened for different plant growth promoting (PGP) activities. The isolate was further identified by 16S rRNA sequencing as Bacillus subtilis MNU16 with IAA concentration (56.95 ± 0.43 6μg/ml), siderophore unit (9.73 ± 2.05%), phosphate solubilization (285.13 ± 1.05 μg/ml) and ACC deaminase activity (116.79 ± 0.019 μmoles α-ketobutyrate/mg/24 h). Further, to evaluate the metal resistance profile of bacterium, the isolate was screened for multi-metal resistance (viz. 900 mg/L for Cr, 600 mg/L for As, 700 mg/L for Ni and 300 mg/L for Hg). Additionally, the resistance pattern of B. subtilis MNU16 against Cr(VI) (from 50 to 300 mg/L) treatments were evaluated. An enriched population was observed at 0–200 mg/L Cr(VI) concentration while slight reductions were observed at 250 and 300 mg/L Cr(VI). Further, the chromium reduction ability at 50 mg/L of Cr(VI) highlighted that the bacterium B. subtilis MNU16 reduced 75% of Cr(VI) to 13.23 mg/L within 72 h. The localization of electron dense precipitates was observed in the TEM images of B. subtilis MNU16 which is might be due to the reduction of Cr(VI) to Cr(III). The data of fluorescence microscopy and flow cytometry with respect to Cr(VI) treatments (50–300 mg/L) showed a similar pattern and clearly revealed the less toxic effect of hexavalent chromium upto 200 mg/L Cr(VI) concentration. However, toxicity effects were more pronounced at 300 mg/L Cr(VI). Therefore, the present study suggests that the plant growth promoting potential and resistance efficacy of B. subtilis MNU16 will go a long way in developing an effective bioremediation approach for Cr(VI) contaminated soils.

Interpenetrating polymer network (IPN) is an enterprising drug delivery system, comprising of two polymers with several advantages like stability, biocompatibility, high swelling capacity and biodegradability which plays an important function in targeted and controlled drug delivery. IPN acquired appreciable focus in the pharmaceutical sector mostly for the last few decades because of their utility in biomedical applications like tissue engineering and drug delivery at the target site at desired rate. For the past few years, different types of polymers obtained from natural or artificial sources have been used to prepare the IPN, resulting in improved properties; thus, IPN is considered in the category of the novel technologies demonstrating the superior performances as compared to the conventional technique. IPN development leads to the formation of dosage form with reduced side effects and prolonged drug action. The current topic includes IPN, types of IPN, mode of preparation, applications, delivery systems and list of polymers employed in the synthesis of IPN.

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A lead-resistant bacterial strain was isolated from coal mine dump and identified as Acinetobacter junii Pb1 on basis of 16S rRNA (ribosomal ribonucleic acid) gene sequencing. The minimum inhibitory concentration of lead for the strain was 16,000 mg l and it showed antibiotic and multi metal resistance. In aqueous culture, at an initial lead (Pb(II)) concentration of 100 and 500 mg l, lead adsorption and accumulation by the isolate was 100 and 60%, at pH 7 at 30 °C after 48 and 120 h, respectively. The two fractions of exopolysaccharide (EPS), loosely associated EPS (laEPS) and bound EPS (bEPS), and whole cells (devoid of EPS) showed high binding affinity towards Pb(II). The binding affinity of laEPS towards Pb(II) (1071 mg Pb g) was three times higher than that of bEPS (321.5 mg Pb g) and 6.5 times higher than that of whole cells (165 mg Pb g). The binding affinity of EPS and whole cells with Pb(II), reported in the current study, is considerably higher as compared to that reported in the literature, till date. SEM analysis, showed an increase in thickness of cells on exposure to Pb(II) and TEM analysis, revealed its accumulation (interior of cell) and its adsorption (with the external cell surface). The isolate was also found to be positive for indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase production which helps in promoting plant growth. Thus, this study provides a new understanding towards Pb(II) uptake by A. junii Pb1, highlighting its potential on the restoration of Pb(II) contaminated repositories.

Aims:  To study the degradation of phorate by a bacterium isolated from phorate‐contaminated sites. Methods and Results:  Ralstonia eutropha strain AAJ1 isolated from soil was found to degrade phorate (supplied as sole carbon source) upto 85% in 10 days in liquid medium. Half‐life (t½) of phorate in the liquid medium in control (uninoculated) and in experimental (inoculated with R. eutropha, strain AAJ1) samples was recorded as 36·49 and 6·29 days, respectively. Kinetics revealed that phorate degradation depends on time and the reaction follows the first order kinetics. Diethyl dithiophosphate was one of the degradation products, which is markedly less toxic than the parent compound; other degradation products included phorate sulfoxide and phorate sulfone. Release of inorganic phosphates and sulfates indicated the potential of the isolate to further degrade the above‐mentioned metabolites to simpler forms. The strain was also found to posses phosphomonoesterase and phosphodiesterase enzymatic activity, which are involved in biodegradation of organophosphorus compounds. Conclusions:  Ralstonia eutropha AAJ1 could degrade and detoxify phorate upto 85% in 10 days in laboratory conditions. Significance and Impact of the Study:  The isolate has the potential to be utilized for remediation of phorate‐contaminated water and soil.