Indole signaling and (micro)algal auxins decrease the virulence of Vibrio campbellii, a major pathogen of aquatic organisms

Vibrio campbellii BAA-1116 was used as a Harveyi clade model organism to determine the impact of indole signaling on virulence. Gene expression analysis of V. campbellii grown in LB35 broth with or without 100 μM indole revealed that indole decreased: (1) V. campbellii virulence in shrimp and prawn challenge assays, (2) exopolysaccharide production, and (3) swimming motility. The results also indicated that indole inhibits quorum sensing-regulated bioluminescence and blocks the three-channel quorum sensing system by interfering with quorum sensing signal transduction. Five biological replicates of V. campbellii were grown in LB35 broth (24 h, 200 rpm, 28°C) with and without 100 μM indole and total RNA was extracted from 5.0E+8 cells. Messenger RNA was isolated from the total RNA extracts, treated with DNase, labeled with biotin, fragmented and hybridized to V. campbellii BAA-1116 whole genome microarrays (520694F, Affymetrix).