Pseudoalteromonas probiotics as potential biocontrol agents improve the survival of Penaeus vannamei challenged with acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus

Acute hepatopancreatic necrosis disease (AHPND) has caused a severe decline of global shrimp production and economic losses. One of the causative agents for AHPND is Vibrio parahaemolyticus (VpAHPND), bearing toxin genes pirABvp. In this study, potential probiotic bacteria CDM8 and CDA22, isolated from the hindgut of healthy Penaeus vannamei, were rod-shaped and motile with a single polar flagellum, and they can form yellow colonies, produce oxidase and hydrolyze gelatin. The possibility of their application against VpAHPND was evaluated. Both strains were found to display antagonistic activity against VpAHPND, which could be inhibited by catalase, and they were identified as Pseudoalteromonas spp. based on phylogenetic analysis. These two bacteria produced extracellular antibacterial compounds, according to the disc diffusion assay. Furthermore, CDM8 or CDA22 as a feed additive could (i) significantly decrease the presumptive Vibrio counts in the hindgut of shrimp (P. vannamei) after being fed for 21 days, compared to that in shrimp fed with the mixture of CDM8 and CDA22 and the commercial feed, and (ii) strikingly reduce the cumulative mortality (vs the control group: 36.7% or 76.7% vs 96.7%) of shrimp when challenged with VpAHPND. In addition, they could decrease copy numbers of pirAvp gene in shrimp, according to the quantitative PCR results. However, there is no synergistic relationship between CDM8 and CDA22 when used together as feed additives. All these results suggested that bacteria CDM8 and CDA22 were anti-VpAHPND probiotic candidates and potential biological control agents against AHPND in shrimp aquaculture.