Isolation and Identification of Quorum Quenching bacteria from fish gut

Abstract- Several gram-negative aquatic pathogens use N-Acyl homoserine lactone (AHL) mediated quorum sensing to control virulence. Application of quorum quenching (QQ) bacteria in aquaculture is an emergent antivirulant strategy to control many aquatic diseases. Three AHL degrading bacterial isolates namely E, L1 and L2 were isolated from the intestine gut of two euryhaline fishes of aquaculture importance, the Etroplus suratensis and Lates calcarifer. The isolate E was isolated from the Etroplus suratensis and the isolates L1 & L2 from the Lates calcarifer. All the three isolates E, L1 & L2 were identified by 16S rRNA gene sequencing as Burkholderia gladioli, Bacillus pumilus and Burkholderia cepacia respectively. Upon analyzing the enzyme production of the isolates, all the three isolates were protease positive and amylase negative. Two Burkholderia isolates were positive to lipase production. Antibacterial activity experiments of the isolates with aquatic pathogens Aeromonas hydrophila and Vibrio harveyi demonstrated the antibacterial activity of isolate E against Vibrio harveyi. All the three bacterial isolates were found to be sensitive to most of the antibiotics tested. To our knowledge this is the first report on quorum quenching Burkholderia species and Bacillus pumilus from fish intestine. This study proposes the three isolates E, L1 and L2 have the potential to use as gut probiotic in aquaculture.