Mechanism of Action of Recombinant Acc-Royalisin from Royal
Jelly of Asian Honeybee against Gram-Positive Bacteria
The antibacterial activity of royalisin, an antimicrobial
peptide from the royal jelly produced by honeybees, has been addressed
extensively. However, its mechanism of action remains unclear.
In this study, a recombinant royalisin, RAcc-royalisin from
the royal jelly of Asian honeybee Apis cerana cerana, was expressed by fusing
with glutathione S-transferase (GST) in Escherichia coli BL21, isolated and
purified. The agar dilution assays with inhibition zone showed that
RAcc-royalisin, similar to nisin, inhibits the growth of Gram-positive
bacteria.
The antibacterial activity of RAcc-royalisin was associated
with its concentration, and was weakened by heat treatment ranging from 55°C to
85°C for 15 min. Both RAcc-royalisin and nisin exhibited the minimum inhibitory
concentrations (MIC) of 62.5 µg/ml, 125 µg/ml, and 250 µg/ml against
Gram-positive bacterial strains, Bacillus subtilis and Micrococcus flavus and
Staphyloccocus aureus in the microplate assay, respectively. However,
RAcc-royalisin did not show antimicrobial activity against tested Gram-negative
bacterial and fungal strains. The antibacterial activity of RAcc-royalisin
agrees well with the decrease in bacterial cell hydrophobicity, the leakage of
260-nm absorbing materials, and the observation by transmission electron
microscopy, all indicating that RAcc-royalisin induced the disruption and
dysfunction of cell walls and membranes.
This is the first report detailing the antibacterial
mechanism of royalisin against Gram-positive bacteria, and provides insight
into the application of recombinant royalisin in food and pharmaceutical
industries as an antimicrobial agent.