Biofloc-Based Enhanced Survival of Litopenaeus vannamei Upon AHPND-Causing Vibrio parahaemolyticus Challenge Is Partially Mediated by Reduced Expression of Its Virulence Genes.

The biofloc system is a relatively new aquaculture technology that offers practical solution to maintain culture water quality by recycling nutrients and improves the health status and resistance of shrimps against microbial infection, yet the mode of action involved remains unclear. This study aimed to unravel the underlying mechanism behind the protective effect of a biofloc system using Litopenaeus vannamei and acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus M0904 strain as a host-pathogen model. The results showed that a biofloc system maintained at a C/N ratio of 15, improves the water quality and contributes to the nutrition of cultured animals as bioflocs might serve as an additional protein source. Furthermore, the study demonstrated that the biofloc system enhances the survival of L. vannamei upon challenge with a V. parahaemolyticus AHPND strain. Remarkably, the results highlight that in the biofloc system, AHPND-causing V. parahaemolyticus possibly switch from free-living virulent planktonic phenotype to a non-virulent biofilm phenotype, as demonstrated by a decreased transcription of flagella-related motility genes (flaA, CheR, and fliS), Pir toxin (PirB VP ), and AHPND plasmid genes (ORF14) and increased expression of the phenotype switching marker AlkPhoX gene in both in vitro and in vivo conditions. Taken together, results suggest that biofloc steer phenotype switching, contributing to the decreased virulence of V. parahaemolyticus AHPND strain toward shrimp postlarvae. This information reinforces our understanding about AHPND in a biofloc setting and opens the possibility to combat AHPND not only by trying to eliminate the AHPND-causing V. parahaemolyticus from the system but rather to steer the phenotypic switch.

The 9H-Fluoren Vinyl Ether Derivative SAM461 Inhibits Bacterial Luciferase Activity and Protects Artemia franciscana From Luminescent Vibriosis.

Vibrio campbellii is a major pathogen in aquaculture. It is a causative agent of the so-called "luminescent vibriosis," a life-threatening condition caused by bioluminescent Vibrio spp. that often involves mass mortality of farmed shrimps. The emergence of multidrug resistant Vibrio strains raises a concern and poses a challenge for the treatment of this infection in the coming years. Inhibition of bacterial cell-to-cell communication or quorum sensing (QS) has been proposed as an alternative to antibiotic therapies. Aiming to identify novel QS disruptors, the 9H-fluroen-9yl vinyl ether derivative SAM461 was found to thwart V. campbellii bioluminescence, a QS-regulated phenotype. Phenotypic and gene expression analyses revealed, however, that the mode of action of SAM461 was unrelated to QS inhibition. Further evaluation with purified Vibrio fischeri and NanoLuc luciferases revealed enzymatic inhibition at micromolar concentrations. In silico analysis by molecular docking suggested binding of SAM461 in the active site cavities of both luciferase enzymes. Subsequent in vivo testing of SAM461 with gnotobiotic Artemia franciscana nauplii demonstrated naupliar protection against V. campbellii infection at low micromolar concentrations. Taken together, these findings suggest that suppression of luciferase activity could constitute a novel paradigm in the development of alternative anti-infective chemotherapies against luminescent vibriosis, and pave the ground for the chemical synthesis and biological characterization of derivatives with promising antimicrobial prospects.

Comparative analysis on natural spawning of F1 meagre, Argyrosomus regius, with wild broodstock spawns in Portugal.

The purpose of this study was to describe and compare the reproductive success and egg and larvae quality between wild and first-generation (F1) breeders of Argyrosomus regius. Wild broodstock were adapted to captivity, and good-quality spawns were obtained in 2009-2010, after GnRH treatment. In 2012, the F1 meagre (3 years old) spawned naturally at IPMA's Aquaculture Research Station facilities. From each spawning event, the following parameters were determined: number of floating and non-floating eggs, egg size, hatching success and larval total length. Eggs size and percentage of hatching obtained from F1 breeders (1.04 ± 0.10 mm and 90.5 ± 6.4%) were significantly higher when compared with wild breeders (0.97 ± 0.13 mm and 17.0 ± 12.7%). Although wild breeder spawns exhibited 2.7 ± 0.2 mm for larval total length, F1 breeder spawns presented 2.6 ± 0.2 mm. The wild and F1 breeder spawns exhibit a good egg and larval quality, indicating a promising starting point for a successful meagre hatchery production.