Antibacterial mechanism of Aspergillus niger xj spore powder crude extract B10 against Agrobacterium tumefaciens T-37

A crude extract (B10) of Aspergillus niger spores showed effective antibacterial activity against Agrobacterium tumefaciens T-37. The inhibition rate was 98.22%, and the half maximal inhibitory concentration was 0.035 ± 0.018 mg/mL. To study the primary antibacterial mechanism, this study used relative electric conductivity, release of proteins and nucleic acids, sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) and detection of reactive oxygen species (ROS). After adding B10, the relative electric conductivity increased in the supernatant indicating electrolyte transport from intracellular to extracellular space. Compared with the control group and the benzylpenicillin potassium (BP) group, the B10 group had a significant increase in extracellular nucleic acid and protein within 0–18 h, showing that the cell and cytoplasmic membranes were damaged by B10. The SDS–PAGE results confirmed that the extracellular protein and nucleic acid levels were in agreement with lower intracellular total protein. Finally, the intracellular levels of ROS indicated that B10 caused an increase in ROS. In summary, B10 showed clear antibacterial activity against A. tumefaciens through damaging cytoplasmic membranes. The research provided a scientific basis for the prevention and treatment of bacteria.