Antibacterial Effect and Mechanism of Chelerythrine on Xanthomonas oryzae pv. oryzae

Abstract

Xanthomonas oryzae pv. oryzae (Xoo) is a biotrophic bacterial pathogen, which causes devastating bacterial blight disease worldwide. In this study, we thoroughly investigated the antimicrobial effect of the plant-derived extract chelerythrine against Xanthomonas oryzae pv. oryzae (Xoo) and elucidated its mechanism. Chelerythrine is a quaternary ammonium alkaloid with a 2,3,7,8-tetrasubstituted phenanthridine structure, extracted from plants, such as the whole plant of Chelidonium majus, and the roots, stems, and leaves of Macleaya cordata. We found that chelerythrine significantly inhibited the growth of Xoo at a concentration of 1.25 μg/mL. Further experiments revealed that chelerythrine interfered with the division and reproduction of the bacterium, leading to its filamentous growth. Additionally, it increased the permeability of Xoo cell membranes and effectively decreased the pathogenicity of Xoo, including the inhibition of extracellular polysaccharide production, cellulase secretion, and biofilm formation. Chelerythrine induced the accumulation of reactive oxygen species in the bacterium, triggering oxidative stress. The result showed that chelerythrine inhibited the formation of the Z-ring of Xoo, interfered with the synthesis of pyrimidine and purine nucleotides, inhibited DNA damage repair, and inhibited the formation of peptidoglycan and lipid-like A, thus interfering with cell membrane permeability, inhibiting carbohydrate metabolism and phosphorylation of sugars, reducing pathogenicity, and ultimately inhibiting bacterial growth and leading to the destruction or lysis of bacterial cells. Altogether, our results suggest that the antimicrobial effect of chelerythrine on Xoo exhibits multi-target properties. Additionally, its effective inhibitory concentration is low. These findings provide a crucial theoretical basis and guidance for the development of novel and efficient plant-derived antimicrobial compounds.

Keywords: Xanthomonas oryzae pv. oryzae; antibacterial action; chelerythrine.

Figure 1

Growth curves of Xanthomonas oryzae pv. oryzae after treatment with different concentrations of chelerythrine.

Figure 2

SEM image of Xoo ((A): SEM image of Xoo untreated with chelerythrine; (B): SEM image of Xoo treated with 1×MIC chelerythrine for 24 h; (C): SEM image of Xoo treated with 1×MIC chelerythrine for 48 h).

Figure 3

(A): The effect of chelerythrine on the permeability of the inner membrane of Xoo. (B): The ratio of the cell membrane permeability rate of each treatment group to that of the control group. a, b, c,: Different letters indicate statistical differences at the level of p < 0.05 between different treatment groups and the control group.

Figure 4

(A): The effect of chelerythrine on the biofilm formation of Xoo. (B): The inhibition rate of cell membranes in each treatment group compared with the control group. a, b, c: Different letters indicate statistical differences at the level of p < 0.05 between different treatment groups and the control group.

Figure 5

The effect of chelerythrine on the pyruvate content of Xoo. a, b, c: Different letters indicate statistical differences at the level of p < 0.05 between different treatment groups and the control group.

Figure 6

The effect of chelerythrine on the cell mobility of Xoo.

Figure 7

The effect of chelerythrine on the ROS of Xoo. a, b, c, d: Different letters in Figure 7 indicate statistical differences at the level of p < 0.05 between different treatment groups and the control group.

Figure 8

Relative expression levels of transcripts.