Tarek Moussa

Chemical fungicides have been used to control fungal diseases like Sclerotinia sclerotiorum. These fungicides must be restricted because of their toxicity and the development of resistance strains. Therefore, utilizing natural nanoscale materials in agricultural production is a potential alternative. This work aimed to investigate the antifungal properties of a nanocomposite (nano-chitosan-coated, green-synthesized selenium nanoparticles) against the plant pathogenic fungus S. sclerotiorum. Chemical reduction was used to produce selenium nanoparticles from citrus peel extracts, and ionotropic gelation was used to produce chitosan nanoparticles. The nanocomposite has been produced using selenium nanoparticles stabilized by chitosan and cross-linked with sodium tripolyphosphate. Transmission electron microscopy, dynamic light scattering, X-ray diffraction, UV-VIS spectroscopy, and Fourier transform infrared spectroscopy were used to characterize all produced nanostructures. The in vitro antifungal activity and minimum inhibitory concentration of all bulk and nanostructures are investigated at (0.5, 1, 5, 10, 50, 100) ppm concentrations. Scanning electron microscopy was used to detect structural deformations in the fungal mycelium. The findings support the successful synthesis and characterization of all nanoparticles. Lemon peel extract produced smaller, more stable, and distributed selenium nanoparticles (42.28 ± 18.5 nm) than orange peel extract (85.7 ± 140.22 nm). Nanostructures, particularly nanocomposite, have shown a considerable increase in antifungal efficacy compared to bulk structures. At a minimum inhibitory concentration of 0.5 ppm, the nanocomposite exhibited 100% inhibitory activity. The nanocomposite with a concentration of 0.5 ppm exhibited the lowest average fungal biomass (0.32 ± 0.05 g) among all tested nanostructures. Fungal hyphae treated with 0.5 ppm of nanocomposite within 18 h of treatment revealed substantial damage and deformation. These results provide new insights into the nanocomposite as an eco-friendly and promising antifungal agent against other plant pathogenic fungi.

Enzymatic production of D-mannose attracts increasing attention because of the health effects and commercial values of D-mannose. Several kinds of epimerases or isomerases have been used for enzymatic production of D-mannose from D-glucose or D-fructose. D-Mannose epimerase (MEase), belonging to N-acyl-D-glucosamine 2-epimerase superfamily enzymes, catalyzes the C-2 epimerization between D-glucose and D-mannose. In this study, a novel MEase was identified from Cytophagaceae bacterium SJW1-29. Sequence and structure alignments indicate that it is highly conserved with the reported R. slithyformis MEase with the known crystal structure. It was a metal-independent enzyme, with an optimal pH of 8.0 and an optimal temperature of 40 °C. The specific activities on D-glucose and D-mannose were 2.90 and 2.96 U/mg, respectively. The Km, kcat, and kcat/Km on D-glucose were measured to be 194.9 mM, 2.72 s−1, and 0.014 mM−1 s−1, respectively. The purified enzyme produced 23.15 g/L of D-mannose from 100 g/L of D-glucose at pH 8.0 and 40 °C for 8 h, with a conversion rate of 23.15 %.

n/a

n/a