Abstract
The bacterium Xanthomonas campestris pv. campestris (Xcc) causes black rot disease in cruciferous crops, resulting in severe yield loss worldwide. The excessive use of chemical pesticides in agriculture to control diseases has raised significant concern about the impact on the environment and human health. Nanoparticles have recently gained significant attention in agriculture owing to their promising application in plant disease control, increasing soil fertility and nutrient availability. In the current study, we synthesized thymol-loaded chitosan nanoparticles (TCNPs) and assessed their antibacterial activity against Xcc. The synthesis of TCNPs was confirmed by using ultraviolet–visible spectroscopy. Fourier-transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy analysis revealed the functional groups, size, and shape of TCNPs, with sizes ranging from 54 to 250 nm, respectively. The antibacterial activity of TCNPs against Xcc was investigated in vitro by liquid broth, cell viability, and live dead staining assay, and all of them demonstrated the antibacterial activity of TCNPs. Furthermore, TCNPs were found to directly inhibit the growth of Xcc by suppressing the growth of biofilm formation and the production of exopolysaccharides and xanthomonadin. The ultrastructure studies revealed membrane damage in TCNP-treated Xcc cells, causing a release of intracellular contents. Headspace/gas chromatography (GC)–mass spectrometry (MS) analysis showed changes in the volatile profile of Xcc cells treated with TCNPs. Increased amounts of carbonyl components (mainly ketones) and production of new volatile metabolites were observed in Xcc cells incubated with TCNPs. Overall, this study reveals TCNPs as a promising antibacterial candidate against Xcc.
Highlights
To meet the global food security challenge, a substantial increase in crop production is required
thymol-loaded chitosan nanoparticles (TCNPs) were synthesized, and the formation of the nanoparticles was visible as an opaque solution, which was confirmed by UV-Vis spectrophotometer, which showed an absorption maximum at 300 nm
The TCNPs exhibited strong bactericidal activity against Xanthomonas campestris pv. campestris (Xcc), which demonstrated a decrease in bacterial growth and cell viability
Summary
To meet the global food security challenge, a substantial increase in crop production is required. The agriculture sector has witnessed an expeditious development of nano-pesticides as an alternative to chemical pesticides where the efficacy of biocontrol agents is enhanced by converting them into nanoparticles or conjugating them with nanoparticles with reduced toxicity and controllable composition These formulations can be used to increase the shelf life of agricultural produce (Ishkeh et al, 2021; Kutawa et al, 2021; Zobir et al, 2021). The inhibitory activity of thyme essential oil-loaded chitosan nanoparticles and nanocapsules has been reported against many foodborne bacterial pathogens (Pecarski et al, 2014) These reports interested us in developing active TCNPs and exploring their activity against Xcc, which is a devastating disease in cruciferous vegetables. The present work provides a comprehensive analysis of the antibacterial action of the eco-friendly chitosan–thymol conjugate nanoparticles towards controlling the bacterial disease of cruciferous vegetables
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