In this study, zinc oxide nanoparticles (ZnO-NPs) were successfully fabricated through the harnessing of metabolites present in the cell filtrate of a newly isolated and identified microalga Arthrospira platensis (Class: Cyanophyceae). The formed ZnO-NPs were characterized by UV–Vis spectroscopy, Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Data showed the efficacy of cyanobacterial metabolites in fabricating spherical, crystallographic ZnO-NPs with a size ≈30.0 to 55.0 nm at a wavelength of 370 nm. Moreover, FT-IR analysis showed varied absorption peaks related to nanoparticle formation. XPS analysis confirms the presence of Zn(II)O at different varied bending energies. Data analyses exhibit that the activities of biosynthesized ZnO-NPs were dose-dependent. Their application as an antimicrobial agent was examined and formed clear zones, 24.1 ± 0.3, 21.1 ± 0.06, 19.1 ± 0.3, 19.9 ± 0.1, and 21.6 ± 0.6 mm, at 200 ppm against Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans, respectively, and these activities were reduced as the NPs concentration decreased. The minimum inhibitory concentration (MIC) values were determined as 50 ppm for S. aureus, 25 ppm for P. aeruginosa, and 12.5 ppm for B. subtilis, E. coli, and C. albicans. More interestingly, ZnO-NPs exhibit high in vitro cytotoxic efficacy against cancerous (Caco-2) (IC₅₀ = 9.95 ppm) as compared with normal (WI38) cell line (IC₅₀ = 53.34 ppm).

An endophytic strain of Streptomyces antimycoticus L-1 was isolated from healthy medicinal plant leaves of Mentha longifolia L. and used for the green synthesis of silver nanoparticles (Ag-NPs), through the use of secreted enzymes and proteins. UV–vis spectroscopy, Fourier-transform infrared (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and dynamic light scattering (DLS) analyses of the Ag-NPs were carried out. The XRD, TEM, and FT-IR analysis results demonstrated the successful biosynthesis of crystalline, spherical Ag-NPs with a particle size of 13–40 nm. Further, the stability of the Ag-NPs was assessed by detecting the surface Plasmon resonance (SPR) at 415 nm for one month or by measuring the NPs surface charge (−19.2 mV) by zeta potential analysis (ζ). The green-synthesized Ag-NPs exhibited broad-spectrum antibacterial activity at different concentrations (6.25–100 ppm) against the pathogens Staphylococcus aureus, Bacillus subtilis Pseudomonas aeruginosa, Escherichia coli, and Salmonella typhimurium with a clear inhibition zone ranging from (9.5 ± 0.4) nm to (21.7 ± 1.0) mm. Furthermore, the green-synthesized Ag-NPs displayed high efficacy against the Caco-2 cancerous cell line (the half maximal inhibitory concentration (IC₅₀) = 5.7 ± 0.2 ppm). With respect to antibacterial and in-vitro cytotoxicity analyses, the Ag-NPs concentration of 100 ppm was selected as a safe dose for loading onto cotton fabrics. The scanning electron microscopy connected with energy-dispersive X-ray spectroscopy (SEM-EDX) for the nano-finished fabrics showed the distribution of Ag-NPs as 2% of the total fabric elements. Moreover, the nano-finished fabrics exhibited more activity against pathogenic Gram-positive and Gram-negative bacteria, even after 10 washing cycles, indicating the stability of the treated fabrics.

In this study, 15 bacterial endophytes linked with the leaves of the native medicinal plant Pulicaria incisa were isolated and identified as Agrobacterium fabrum, Acinetobacter radioresistant, Brevibacillus brevis, Bacillus cereus, Bacillus subtilis, Paenibacillus barengoltzii, and Burkholderia cepacia. These isolates exhibited variant tolerances to salt stress and showed high efficacy in indole-3-acetic acid (IAA) production in the absence/presence of tryptophan. The maximum productivity of IAA was recorded for B. cereus BI-8 and B. subtilis BI-10 with values of 117 ± 6 and 108 ± 4.6 μg mL⁻¹, respectively, in the presence of 5 mg mL⁻¹ tryptophan after 10 days. These two isolates had a high potential in phosphate solubilization and ammonia production, and they showed enzymatic activities for amylase, protease, xylanase, cellulase, chitinase, and catalase. In vitro antagonistic investigation showed their high efficacy against the three phytopathogens Fusarium oxysporum, Alternaria alternata, and Pythium ultimum, with inhibition percentages ranging from 20% ± 0.2% to 52.6% ± 0.2% (p ≤ 0.05). Therefore, these two endophytic bacteria were used as bio-inoculants for maize seeds, and the results showed that bacterial inoculations significantly increased the root length as well as the fresh and dry weights of the roots compared to the control plants. The Zea mays plant inoculated with the two endophytic strains BI-8 and BI-10 significantly improved (p ≤ 0.05) the growth performance as well as the nutrient uptake compared with an un-inoculated plant.

The aqueous extract of marine green macroalgae, Ulva fasciata Delile, was harnessed for the synthesis of zinc oxide nanoparticles (ZnO-NPs). The conversion to ZnO-NPs was characterized by color change, UV–vis spectroscopy, FT-IR, TEM, SEM-EDX, and XRD. Data showed the formation of spherical and crystalline ZnO-NPs with a size range of 3–33 nm. SEM-EDX revealed the presence of Zn and O in weight percentages of 45.3 and 31.62%, respectively. The phyco-synthesized ZnO-NPs exhibited an effective antibacterial activity against the pathogenic Gram-positive and Gram-negative bacteria. The bacterial clear zones ranged from 21.7 ± 0.6 to 14.7 ± 0.6 mm with MIC values of 50–6.25 µg mL⁻¹. The catalytic activity of our product was investigated in dark and visible light conditions, using the methylene blue (MB) dye. The maximum dye removal (84.9 ± 1.2%) was achieved after 140 min in the presence of 1.0 mg mL⁻¹ of our nanocatalyst under the visible light at a pH of 7 and a temperature of 35 °C. This percentage was decreased to 53.4 ± 0.7% under the dark conditions. This nanocatalyst showed a high reusability with a decreasing percentage of ~5.2% after six successive cycles. Under the optimum conditions, ZnO-NPs showed a high efficacy in decolorizing the tanning wastewater with a percentage of 96.1 ± 1.7%. Moreover, the parameters of the COD, BOD, TSS, and conductivity were decreased with percentages of 88.8, 88.5, 96.9, and 91.5%, respectively. Moreover, nano-ZnO had a high efficacy in decreasing the content of the tanning wastewater Cr (VI) from 864.3 ± 5.8 to 57.3 ± 4.1 mg L⁻¹ with a removal percentage of 93.4%.

Hexavalent chromium Cr (VI) is a toxic heavy metal that discharged by many industries into the water streams. It is the most poisoned form of chromium compounds that destroy the ecosystem. Microalgal species, Chlorella sp., was used as a biosorbent material to remove Cr (VI) from the Cr-contaminated effluents. Furthermore, different variables: pH, temperature, contact time, Cr (VI) concentration and algal dose were optimized in order to determine the optimum conditions that achieve the highest removal efficiency. Optimization process was achieved through two steps: one factor at a time (OFAT) experiments followed by 2⁵ general full factorial. Moreover, molecular identification was performed using 18S rRNA in order to demonstrate the species of Chlorella and it was identified as Chlorella sorokiniana. The highest chromium removal efficiency of 99.6793% was achieved at 100 ppm Cr (VI) after three days contact time. Chlorophyll ‘a’ estimation as a growth indicator stated that Chlorella sorokiniana can tolerate 100 ppm Cr (VI) for three days exposure. The results suggested that Chlorella sorokiniana is a good biosorbent material and it distinguished by its high ability to uptake Cr (VI) from solutions.