Antibacterial activity of an anti-lipopolysaccharide factor (MjALF-D) identified from kuruma prawn (Marsupenaeus japonicus).

Antimicrobial peptides (AMPs) play important roles in host innate immune systems. Anti-lipopolysaccharide factor (ALF), which is a primary AMP in crustaceans, is active against bacteria, fungi and some viruses. MjALF-D, an anionic peptide, is a group D ALF isolated from Marsupenaeus japonicus. In the present study, a series of experiments were performed to study its antibacterial spectrum and further explore its antibacterial and bacterial binding activities. Liquid growth inhibition data demonstrated that recombinant MjALF-D (rMjALF-D) possessed strong antibacterial activity against the gram-positive bacterium Micrococcus luteus and the gram-negative bacterium Photobacterium damselae , with a minimum inhibitory concentration (MIC) or minimum bactericidal concentration (MBC) lower than 1.25 μM. The kinetic analysis showed that the antibacterial activity of rMjALF-D was dose- and time-dependent. Additionally, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations the potential bactericidal process. rMjALF-D treatment resulted in a large number of unidentified filamentous structures wrapped around the bacteria, and during the incubation, the cell surface became obviously rough and disrupted. rMjALF-D showed distinct binding ability after direct incubation with M. luteus and P. damselae but no binding ability to Escherichia coli , which was weakly inhibited by rMjALF-D. These data suggest that MjALF-D displays modest antibacterial activity and may provide more insights into the function and role of ALF in shrimp immunity. • Based on the detection of its antibacterial spectrum, rMjALF-D exerted modest bactericidal activity. • The bactericidal activity of rMjALF-D against bacteria is dependent on both the dose and time. • rMjALF-D could induce leakage of the cytoplasmic content of the bacteria. • rMjALF-D binds to Micrococcus luteus and Photobacterium damselae but not to Escherichia coli. • rMjALF-D played multiple roles in the bactericidal process. [ABSTRACT FROM AUTHOR]