Development of liposomal juglone formulation and determination of antibacterial activity on tomato pathogens

Plant-based natural antibacterial agents play an effective role in controlling drug-resistant strains. One of these actives, juglone, stands out as a molecule with strong antimicrobial properties and wide application areas for the control of plant diseases. Its disadvantages, such as insolubility in water, easy oxidation and poor bioavailability, limit its use in industry. The use of nanocarriers such as liposomes for the delivery of juglone is a strategy that can overcome these limitations. To overcome the problems encountered in liposomal encapsulation of hydrophobic substances, researchers are incorporating cyclodextrins into liposomal drug formulations to improve their properties. In this thesis; it was aimed to study the encapsulation of the juglon/β-cyclodextrin inclusion complex produced for the first time in the literature. The inclusion ratio, loading capacity and reaction efficiency of the complex were investigated, and the encapsulation efficiency, size, polydispersity index (PDI), and zeta potential of the formulation were determined. Fourier transform infrared spectroscopy (FT-IR) was used for physicochemical characterization, and scanning electron microscopy (SEM) was used for morphological characterization.Juglone release was studied in vitro by dialysis method. Antibacterial activities of Pseudomonas syringae pv. tomato (SH-1), Xanthomonas euvesicatoria (SH-2) and Clavibacter michiganensis subsp. michiganensis (SH-3) were investigated in vitro using agar disk diffusion and microdilution methods. When the concentration at which antibacterial activity was observed was determined, the effect of the formulations applied based on this concentration on tomato seed germination was observed for 14 days. The inclusion rate, loading capacity and reaction efficiency of the prepared inclusion complexes were 79.3%, 11.8% and 89.4%, respectively. The encapsulation efficiency of the juglone/β-cyclodextrin liposomal formulation was 72.88%, the size was 106.1 ± 0.5 nm, the PDI value was 0.247 ± 0.012, and the zeta potential was -49.2 ± 1.36 mV. FTIR results show that the juglone is mostly in the β-CD cavity and liposomal encapsulation is also successful. SEM results confirm the formation of round particles with smooth surfaces and a uniform size distribution. The release study showed that the release of juglone from liposomes had a biphasic release profile and the cumulative release was 46.73% at 72 hours. According to the agar disk diffusion test, the J/β-CD/L formulation showed an inhibition zone of 9 mm on Pst, 10.6 mm on Xeu and 8 mm on Cmm. The MIC values of J/β-CD/L molecule on SH-1, SH-2 and SH-3 were 68.93 µg/mL, 34.47 µg/mL and 68.93 µg/mL, respectively, and the MBC values were 68.93 µg/mL, 68.93 µg/mL and 137.87 µg/mL, respectively. The controlled release of J/β-CD/L resulted in a determined antibacterial activity that was found to be 2 times higher than that of free juglone for all three pathogenic bacterial species tested. According to the seed germination test, the most germinated set at the end of the 14th day was the seeds treated with the formulation containing 73.75 µg/ml free juglone at a concentration of 0.625 mg/mL J/β-CD/L and the germination percentage was 86.67%. In summary, the liposomal encapsulation of J/β-CD/L, developed as part of the thesis, resulted in enhanced solubility of juglone, a hydrophobic molecule, and contributed to improved bioavailability of the substance.