Inhibitory mechanism of bacilosarcin B from Bacillus subtilis against Photobacterium damselae

Abstract:

[Background] The marine pathogenic bacterium, Photobacterium damselae, causes various diseases in marine organisms and humans. Therefore, it is of great significance to investigate the approaches for the biocontrol of P. damselae. [Objective] To investigate the activity and mechanism of bacilosarcin B from Bacillus subtilis in inhibiting P. damselae.[Methods] Bacilosarcin B was prepared from the fermentation broth of B. subtilis fmb60 by high-performance liquid chromatography. The minimum inhibitory concentration of bacilosarcin B against various pathogenic bacteria and the time-kill curve against P. damselae were determined using a spectrophotometer. The impacts of bacilosarcin B on the biofilm, extracellular nucleic acids, proteins, and intracellular alkaline phosphatase content of P. damselae were assessed. Fluorescence microscope, scanning electron microscope, and transmission electron microscope were employed to examine the cell membrane permeability and cell wall integrity of P. damselae. Finally, the effects of bacilosarcin B on bacterial motility and intracellular DNA were studied. [Results] The minimum inhibitory concentration of bacilosarcin B against P. damselae was 8 μg/mL. Bacilosarcin B disrupted the integrity of bacterial cell walls and cell membranes and increased membrane permeability to cause the leakage of cellular components. Additionally, it bound to intracellular DNA by the manner similar to the insertion of ethidium bromide into DNA. [Conclusion] Bacilosarcin B exhibits a significant inhibitory effect on P. damselae and has the potential to be developed as a novel antibacterial agent, which is of significance for the healthy development of marine aquaculture.