Evaluation of phenolic compounds and antimicrobial activities in transgenic Codonopsis lanceolata plants via overexpression of the γ-tocopherol methyltransferase (γ-tmt) gene

Abstract

This study was carried out to investigate antimicrobial activities of leaf and root extracts of transgenic Codonopsis lanceolata with over-expressing γ-tocopherol methyl transferase (γ-tmt) gene. The antimicrobial activity was assessed using the agar disc diffusion method and minimum inhibitory concentration (MIC) method, and the extracts from the transgenic C. lanceolata were compared with those of the wild plants by using the in-vitro antimicrobial assays with five pathogenic bacteria and two yeast species. The results indicated that transgenic C. lanceolata overexpressing γ-tmt possesses antimicrobial activity against both gram-positive and gram-negative bacteria. Transgenic lines showed increased antimicrobial activity, ranging from 1.90 ± 0.50 to 5.50 ± 0.77 mm in the leaf extract of transgenic C. lanceolata, compared to the extract from the control plants, ranging from 1.27 ± 0.50 to 4.73 ± 0.40 mm. Staphylococcus aureus was the most susceptible microorganism to transgenic leaf extracts with lower MICs (500 μg/mL) and higher growth inhibition zones (5.33 mm). Leaf extract of transgenic plants showed antimicrobial activity against Salmonella typhimurium, Klebsiella pneumoniae, and Escherichia coli. However, transgenic root extract showed lower antimicrobial activity against all tested microorganisms, with MIC > 1000 μg/mL. The a-tocopherol content of the plants was enhanced by the overexpression of (γ-tmt) gene compared to control plant. We observed an increase in the phenolic compound concentration in transgenic leaves. The predominant phenolic compounds that increased in the transgenic leaf were chlorogenic acid, luteolin, benzoic acid, and apigenin. The antimicrobial activity of transgenic C. lanceolata was strongly correlated to the concentration of phytochemical compounds. These results may help to identify novel natural antimicrobial agents that could be used against infectious diseases.