Preliminary study of screening and characteristics of strains with Quorum sensing inhibition activity in shrimp culture environment

We screened the active strains with Quorum sensing inhibition activity in shrimp gut and their culture environment, to investigate the environmental factors that affect the activity of strains and their effects on the virulence gene expression of Vibrio campbellii. The methods of filter paper and high-throughput were applied to screen active strains. The effects of AHLs signal molecule on active strains growth with different culture time and salinities were estimated. The effects of crude extract products of active strains on the virulence genes toxR and tlh mRNA expression levels of the pathogenic bacteria were also investigated. Two active strains named as DC13 and RS5 were obtained and preliminarily identified as Bacillus subtilis and B.megaterium by 16S rRNA gene sequence analysis. No significant difference was observed in the active strains growth treated with AHLs signaling molecule (P>0.05). The AHLs signal molecule degradation ability of strain DC13 reached the maximum value at 24^th hour. However, after a 12—48 h treatment, no significant difference was observed in AHLs signal molecule degradation ability by strain RS5. When the strains were cultured at salinity of 10–30, there was no significant difference in AHLs signal molecule degradation ability by strain DC13, while significant difference was observed by AHLs signal molecule degradation ability of strain RS5 (P<0.05). It is demonstrated that addition of crude extract products of active strains can increase virulence gene toxR expression but decrease virulence gene tlh expression level.