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the increasing heavy metal contamination in agricultural soils has become a serious concern across the globe. The present study envisages developing microbial inoculant approach for agriculture in Zn contaminated soils. Potential zinc tolerant bacteria (ZTB) were isolated from zinc (Zn) contaminated soils of southern Rajasthan, India. Isolates were further screened based on their efficiency towards Zn tolerance and plant growth promoting activities. Four strains viz. ZTB15, ZTB24, ZTB28 and ZTB29 exhibited high degree of tolerance to Zn up to 62.5 mM. The Zn accumulation by these bacterial strains was also evidenced by AAS and SEM-EDS studies. Assessment of various plant growth promotion traits viz., iAA, GA 3 , nH 3 , Hcn, siderophores, Acc deaminase, phytase production and p, K, Si solubilization studies revealed that these ZTB strains may serve as an efficient plant growth promoter under in vitro conditions. Gluconic acid secreted by ZTB strains owing to mineral solubilization was therefore confirmed using high performance liquid chromatography. A pot experiment under Zn stress conditions was performed using maize (Zea mays) variety (FEM-2) as a test crop. Zn toxicity reduced various plant growth parameters; however, inoculation of ZTB strains alleviated the Zn toxicity and enhanced the plant growth parameters. The effects of Zn stress on antioxidant enzyme activities in maize under in vitro conditions were also investigated. An increase in superoxide dismutase, peroxidase, phenylalanine ammonia lyase, catalase and polyphenol oxidase activity was observed on inoculation of ZTB strains. Further, ZIP gene expression studies revealed high expression in the ZIP metal transporter genes which were declined in the ZTB treated maize plantlets. The findings from the present study revealed that ZtB could play an important role in bioremediation in Zn contaminated soils.

Zinc oxide (ZnO) nanoparticles have attracted significant interest in a number of applications ranging from electronics to biomedical sciences due to their large exaction binding energy (60 meV) and wide bandgap of 3.37 eV. In the present study, we report the low-cost bacterium based "eco-friendly" efficient synthesis of ZnO nanoparticles by using the zinc-tolerant bacteria Serratia nematodiphila. The physicochemical characterization of ZnO nanoparticles was performed by employing UV-vis spectroscopy, XRD, TEM, DLS, Zeta potential, and Raman spectroscopy. The antimicrobial and antifungal studies were investigated at different concentrations using the agar well-diffusion method, whereby the microbial growth rate decreases with the increase in nanoparticle concentration. Further, photocatalytic performance studies were conducted by taking methyl orange (MO) as a reference dye.

The breaking silence between the plant roots and microorganisms in the rhizosphere affects plant growth and physiology by impacting biochemical, molecular, nutritional, and edaphic factors. The components of the root exudates are associated with the microbial population, notably, plant growth-promoting rhizobacteria (PGPR). The information accessible to date demonstrates that PGPR is specific to the plant's roots. However, inadequate information is accessible for developing bio-inoculation/bio-fertilizers for the crop in concern, with satisfactory results at the field level. There is a need to explore the perfect candidate PGPR to meet the need for plant growth and yield. The functions of PGPR and their chemotaxis mobility toward the plant root are triggered by the cluster of genes induced by the components of root exudates. Some reports have indicated the benefit of root exudates in plant growth and productivity, yet a methodical examination of rhizosecretion and its consequences in phytoremediation have not been made. In the light of the afore-mentioned facts, in the present review, the mechanistic insight and recent updates on the specific PGPR recruitment to improve crop production at the field level are methodically addressed.

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In the present study, 24 Azotobacter strains were isolated from soils of different areas of southern Rajasthan and characterized at biochemical, functional, and molecular levels. The isolated Azotobacter strains were gram negative and cyst forming when viewed under the microscope. These strains were also screened for their plant growth promoting activities and the ability of these isolates to survive under abiotic stress conditions viz. salt, pH, temperature, and drought stress. All the isolates showed IAA, siderophore, HCN, and ammonia production, whereas seven Azotobacter strains showed phosphate solubilization. Amplified Ribosomal DNA Restriction Analysis (ARDRA) revealed significant diversity among Azotobacter strains and the dendrogram obtained differentiated twenty-four of the strains into two major clusters at a similarity coefficient of 0.64. Qualitative and quantitative N2 fixation abilities of these strains were also detrained, and the amounts of acetylene reduced by Azotobacter strains were in the range of 1.31 to 846.56 nmol C2H4 mg protein−1 h−1. The strains showing high nitrogen fixation ability with multiple PGP activities were selected for further pot studies, and these Azotobacter strains significantly increased the various plant growth parameters of maize plantlets. Furthermore, the best Azotobacter isolates were subjected to 16S rRNA sequencing and confirmed their identities as Azotobacter sp. The indigenous Azotobacter strains with multiple PGP activities could be further used for commercial production.