The photocatalytic antibacterial molecular mechanisms towards Pseudomonas syringae pv. tabaci by g-C3N4 nanosheets: insights from the cytomembrane, biofilm and motility disruption

BACKGROUND Antibacterial photocatalytic therapy has been employed as a promising strategy to combat antibiotic-resistant bacteria in the water disinfection field, especially some non-metal inorganic nanomaterials. However, their antibacterial activities on plant phytopathogens are poorly understood. Here, the photocatalytic antibacterial mechanism of the urea-synthesized graphitic carbon nitride nanosheets (g-C3N4 nanosheets) against Pseudomonas syringae pv. tabaci was systematically investigated in vitro and in vivo. RESULTS The g-C3N4 nanosheets exhibited remarkable concentration-dependent and irradiation-time-dependent antibacterial properties, and the 0.5 mg mL(-1) concentration ameliorated tobacco wildfire disease in host plants. Specifically, under visible irradiation, g-C3N4 nanosheets produced numerous reactive oxygen species (ROS), supplementing the plentiful extracellular and intracellular ROS in bacteria. After exposing light-induced g-C3N4 nanosheets for 1 h, 500 genes were differentially expressed, according to transcriptome analyses. Notably, the expression of genes related 'antioxidant activity' and 'membrane transport' was sharply upregulated, and those related to 'bacterial chemotaxis', 'biofilm formation', 'energy metabolism' and 'cell motility' were downregulated. After exposure for over 2 h, the longer-time pressure on the target bacteria cause the decreased biofilm formation and flagellum motility, further injuring the cell membranes leading to cytoplasm leakage and damaged DNA, eventually resulting in the bacterial death. Concomitantly, the attachment of g-C3N4 nanosheets was a synergistic physical antibacterial pathway. The infection capacity assessment also supported the earlier supposition. CONCLUSION These results provide novel insights into the photocatalytic antibacterial mechanisms of g-C3N4 nanosheets at the transcriptome level, which are expected to be useful for dissecting the response pathways in antibacterial activities and for improving g-C3N4-based photocatalysts practices in plant disease control.

Automated summary

The urea-synthesized graphitic carbon nitride nanosheets demonstrated concentration- and irradiation-time-dependent antibacterial properties against Pseudomonas syringae pv. tabaci, inducing upregulation of genes related to antioxidant activity and membrane transport while downregulating genes related to bacterial chemotaxis, biofilm formation, energy metabolism, and cell motility. The photocatalytic action of g-C3N4 nanosheets led to increased reactive oxygen species production, biofilm disruption, flagellum motility inhibition, cell membrane damage, cytoplasm leakage, and ultimately bacterial death, highlighting a synergistic physical antibacterial pathway.