Combined Fungal Culture Filtrate and Zinc Oxide Nanoparticles Enhance Callus Induction and Antibacterial Bioactivity in Tissue-Cultured Aloe vera (L.) Burm.f.

Abstract

Background: Conventional propagation takes too long and the field related variability in the composition of secondary metabolites affects the production of standardized bioactive Aloe vera biomass.
Methods: Leaf explants taken from Aloe vera were grown on Murashige and Skoog medium containing 2,4-D and BAP. The treatments were arranged in a completely randomized 2 × 2 factorial design: untreated control, sterile Purpureocillium lilacinum cell free culture filtrate, ZnO nanoparticles (30 mg L⁻¹) and filtrate + ZnO-NP treatment. Then callus induction, callus volume, fresh weight and morphology was measured after 4 weeks. The methanolic callus extracts were analysed for phytochemical markers, HPLC detectable Aloe markers and MIC/MBC values of callus extracts against the microorganisms Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa. Two-way ANOVA and Tukey's HSD test was used for data analysis. Conclusion: The combined treatment resulted in maximum callus induction (84.00 ± 6.40%) and callus volume (698.30 ± 65.10 mm³) and fresh weight (1.12 ± 0.13 g) along with compact bright green callus morphology. It also enhanced total phenolics, flavonoids, anthraquinones, aloin A+B and aloe-emodin levels in comparison with untreated callus. The combined treatment showed the highest antibacterial activity with an inhibition zone against S. aureus (16.64 ± 1.07 mm), B. subtilis (13.74 ± 1.08 mm), E. coli (12.76 ± 0.88 mm) and P. aeruginosa (10.96 ± 0.82 mm), and better MIC/MBC values. There were significant interaction effects for growth traits and antibacterial endpoints, with interaction effects being more apparent for the latter.
Conclusions: Under the in vitro conditions used in this study, combined fungal-filtrate and ZnO-NP elicitation proved to be highly effective in boosting the productivity of callus of Aloe vera and enhancing the phytochemical and antibacterial potential of callus extracts. The results showed that the nano-biological elicitation approach would be a suitable method for generating standardized Aloe vera callus biomass with enhanced in vitro antibacterial activity of the callus extract.