الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The exploitation of microorganisms for the synthesis of nanoparticles has gained a great attention these days due to its simplicity, cost-effective, and safety advantages over other approaches. In this work, out of fifty-five actinomycetes isolates, the isolate that coded A8 new3 was chosen for the bio-fabrication of zinc oxide nanoparticles (ZnO-NPs). The isolate was identified via classical approach (phenotypic, physiological, and biochemical characteristics) as Streptomyces violaceoruber and confirmed molecularly (16S rRNA sequence) and deposited in the GenBank database as Streptomyces violaceoruber SYA3 under accession number KX077913. The bio-fabricated ZnO-NPs were characterized using UV-vis, TEM, SEM, FTIR, TGA, and EDX. The obtained results revealed that ZnO-NPs were hexagonal and quasi-spherical in shape with average particle size of 11.7nm. Statistical experimental designs (Plackett-Burman and Box-Behnken) were applied to optimize S. violaceoruber SYA3 biomass production. The new optimized medium formula obtained by applying these strategies produced a biomass weight of 14.8 g/l, which was 4.5 times more than that obtained by the basal medium. Scaling-up production via submerged fermentation system was performed using bench-top fermentor (9L) via batch fermentation mode and fed-batch fermentation mode using the exponential pulses feeding regime of glucose. The S. violaceoruber SYA3 biomass recorded via fed-batch mode (59.3g/l) was 3.9 times higher than the yield obtained under the shake flask conditions. Additionally, ZnO-NPs yield obtained by using fed-batch mode was recorded as 123.7g/l which exceeded by 6.7 times the yield obtained by the shake flask culture. The bio-fabricated ZnO-NPs reaction conditions were improved via Taguchi experimental design. The application of the new conditions (5M of precursor concentration, 100% reductant concentration, and pH 7) recorded 464.95 g/l that increased by 132.8 times the yield obtained from the basal conditions. The antimicrobial activity of ZnO-NPs (1M) against different plant pathogenic bacteria and fungi was investigated. The bio-fabricated ZnO-NPs showed a strong antibacterial activity against Erwinia carotovora (50±0.6mm) followed by Acetobacter pasteurianus (40.3±2.9mm), Clavibacter michiganensis (40.1±1.3mm) and Erwinia persicina (30.4±0.5mm). Moreover, the bio-fabricated ZnO-NPs were able to inhibit the growth of some phytopathogenic fungi such as Alternaria alternata (60.3±3.8mm) followed by Helminthosporium sp. (50.2±3.4mm), then Fusarium moniliforme (40.6±2mm), Phytophthora arenaria (30.4±1.5mm), and Botrytis sp. (20.5±0.5mm). The effect of different concentrations of the bio-fabricated ZnO-NPs (0.1, 0.5, 1, 5 and 10 mg/ml) on the germination of maize seeds was evaluated. The results showed that all ZnO-NPs concentrations had a stimulatory effect on maize seeds since the germination percentage was significantly increased (p≤ 0.05). The bio-fabricated ZnO-NPs as a potential nano-fungicide and/or nano-fertilizer was studied under greenhouse conditions. The treatment of ZnO-NPs (G5) had the ability to reduce the spotting disease caused by A. alternata. The reduction percentage of the spot disease was 72.84%. The same treatment (G5) also had the ability to stimulate the growth of maize leaves and roots with 426.74% and 558.96%, respectively, compared to the control. Additionally, the application of ZnO-NPs as an effective nano-fungicide and/or nano-fertilizer was studied via open field conditions through two successive seasons (2017 & 2018). The reduction percentages of the spot disease caused by A. alternata were 86.58% and 84.27% in 2017 and 2018, respectively. Moreover, the same treatment (Z2) showed the highest stimulation effect of ZnO-NPs on maize plant. Compared to the control, the fresh weights of leaves and roots were stimulated by 855.04% and 782.45%, respectively, in season 2017. Meanwhile, in season 2018 the leaves and roots fresh weights were stimulated by 654.79% and 654.79%, respectively.