Study of quorum quenching bacteria Cobetia sp. reducing the mortality of Penaeus vannamei infected with Vibrio harveyi: in vitro and in vivo tests

Abstract

Finding alternative measures to antibiotics for shrimp bacterial disease management is a current need. The application of quorum quenching (QQ) bacteria to prevent bacterial diseases in aquaculture is a current research hotspot, but the effect and mechanism of QQ bacteria in the practical application of shrimp farming requires further exploration. In the present study, in vitro and in vivo tests were conducted to comprehensively analyze the effect and mechanism of the QQ bacteria W1B (Cobetia sp.) in preventing shrimp vibriosis caused by Vibrio harveyi HAH. Cocultivation of strains W1B and HAH was used to conduct an in vitro test. Strain W1B and its intracellular and extracellular proteins could significantly reduce the concentration of quorum sensing (QS) signaling molecules (AHLs) of V. harveyi HAH without affecting its growth. The intracellular proteins of strain W1B could significantly reduce the expression of the QS regulatory gene luxR and virulence genes of strain HAH. An in vivo test was performed by adding strain W1B to shrimp culture water. Shrimp were cultured for 35 days, and then a challenge test was performed by injecting strain HAH into the shrimp. The results showed that strain W1B at low concentrations (1 × 104 CFU·mL−1) reduced the expression of shrimp immune genes and that high concentrations (1 × 106 CFU·mL−1) increased the expression of SOD, LZM, and IMD. In the challenge test, strain W1B could significantly reduce the mortality and protect the hepatopancreas epithelial cells of shrimp. Additionally, strain W1B could change the expression patterns of shrimp immune-related genes. The relative expression levels of the QS regulatory gene and virulence genes of strain HAH in the shrimp hepatopancreas were significantly downregulated by strain W1B. Additionally, strain W1B significantly reduced the relative expression of shrimp apoptosis-related genes. The above results indicated that QQ strain W1B could inhibit the transcriptional expression of V. harveyi luxR and induce the downregulation of virulence gene expression, thereby reducing V. harveyi pathogenicity. Ultimately, strain W1B could reduce shrimp mortality. These findings can provide new methods and basic data for the prevention and treatment of shrimp bacterial diseases.