Protective Efficacy of a Pseudoalteromonas Strain in European Abalone, Haliotis tuberculata , Infected with Vibrio harveyi ORM4

The hemolymph of healthy marine invertebrates is known to harbor antibiotic-producing bacteria belonging to the genus Pseudoalteromonas . Such strains are potential probiotics to control infectious diseases in aquaculture. In the present study, we screened a collection of Pseudoalteromonas strains isolated from the hemolymph of oyster and mussel for antimicrobial activity against Vibrio harveyi , a pathogenic species responsible for high mortality in abalone . Subsequently, the protective efficacy of the most active strain named h Cg -6 was investigated in abalone culture faced with a Vibrio harveyi ORM4 infection. First, we have controlled the Pseudoalteromonas h Cg -6 safety for abalone health. To that end, animals were immersed for 4 h in Pseudoalteromonas h Cg -6 suspensions in seawater. The abalone viability was monitored and Pseudoalteromonas h Cg -6 was tracked by quantitative-PCR in abalone hemolymph. After immersion, no abalone death occurred while the strain h Cg -6 was significantly detected in hemolymph. Therefore, the strain h Cg -6 was considered safe for abalone and evaluated for its ability to protect abalone against V. harveyi (injection of 1 × 10 3 Vibrio per animal). A 4-h long immersion of abalone in a seawater suspension of Pseudoalteromonas h Cg -6 (1 × 10 6 CFU mL −1 ) prior to infection with Vibrio harveyi significantly improved the abalone viability. Indeed, 15 days post infection, the h Cg -6 treatment used increased the abalone survival rate from 16% in untreated animals to 40% in treated abalone. We hypothesized that Pseudoalteromonas h Cg -6 antibacterial activity increased the hemomicrobiota shielding effect. In conclusion, Pseudoalteromonas h Cg -6 is a promising anti- Vibrio strain for abalone culture.