Abstract
Royal jelly (RJ), a natural honeybee product, has a wide range of antibacterial activities. N-glycosylated major royal jelly protein 2 (N-MRJP2), purified from RJ, can inhibit the growth of Paenibacillus larvae (P. larvae, Gram-positive), a contagious etiological agent of the American foulbrood disease of honeybees. However, the inhibitory mechanism is largely unknown. Antibacterial assay and membrane proteome were conducted to investigate the inhibition capacity of RJ from different instar larvae and P. larvae treated by N-MRJP2, respectively. The similar antibacterial efficiency of RJ from different larval instar indicates that RJ is vital for the adaptive immune defense of small larvae. The killing of P. larvae by N-MRJP2 is achieved by disturbing the cell wall biosynthesis, increasing the permeability of cell membrane, hindering aerobic respiration, restraining cell division and inducing cell death. This demonstrates that RJ is critical for the passive immunity of immature larvae and N-MRJP2 can be used as natural antibiotic substance to resist P. larvae, even for other gram-positive bacteria. This constitutes solid evidence that RJ and N-MRJP2 have potentials as novel antibacterial agents.
Highlights
American foulbrood (AFB), caused by the spore-forming bacterium Paenibacillus larvae subsp. larvae (P. larvae), is a contagious and lethal disease that threatens honeybees.Honeybee larvae are the most susceptible to be infected during the first two days after hatching, while adults are immune to the infection even if a large number of spores are ingested [1]
No differences were found among the diameter of inhibitory zones after the comparison of the Royal jelly (RJ) harvested at different larval instar on each bacterial strain (Figure 1B)
The antibacterial capacity was positively correlated with the concentration of RJ aqueous solution compared to the blank controls (Figure S1)
Summary
Honeybee larvae are the most susceptible to be infected during the first two days after hatching, while adults are immune to the infection even if a large number of spores are ingested [1]. The genome sequencing of two P. larvae strains, ascribed to ERIC II (DSM 25430) and ERIC I (DSM 25719), reveals the frequent genome rearrangements and a high degree of genome plasticity. This in turn affects the phenotype, including morphology [2], metabolic capacity [3], and most importantly in virulence and virulence factors [4,5].
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