Quorum quenching Bacillus spp.: an alternative biocontrol agent for Vibrio harveyi infection in aquaculture.

Quorum sensing (QS) is a type of cell to cell communication in bacteria that can also regulate the virulence potential in pathogenic strains. Hence, QS disruption, i.e. the quorum quenching (QQ) mechanism, is presently being explored as a novel bio-control strategy to counter bacterial infections. In the present study, we characterized the QQ ability of Bacillus spp. strains to reduce the expression of some virulence factors of a shrimp pathogen, Vibrio harveyi. We screened a total of 118 spore-forming bacterial isolates from aquaculture ponds and mangrove soil for their ability to degrade the synthetic N-acyl-homoserine lactones (AHLs) C4-HSL, C6-HSL, C8-HSL, and C10-HSL. We then selected the top 17 isolates with high AHL-degradation ability for further study. Among them, B. subtilis MFB10, B. lentus MFB2, and B. firmus MFB7 had the highest ability for degradation. These 3 isolates suppressed the expression of virulence genes encoding protease, lipase, phospholipase, caseinase, chitinase, and gelatinase, and potentially inhibited the biofilm formation of V. harveyi MFB32. The reduction in expression of virulence genes like those coding for metalloprotease, serine protease, and haemolysin were confirmed by real-time PCR analysis. Moreover, in an in vivo challenge experiment, these Bacillus spp. protected Penaeus monodon post-larvae against V. harveyi MFB3 infection. Our results demonstrate the potential application of AHL-degrading Bacillus spp. as an alternative to antibiotics in shrimp hatcheries to control luminescent vibriosis. This novel bio-therapeutic method is a promising approach towards disease control in shrimp aquaculture.