Introduction
The aquaculture industry is continuously interested in innovative practices with the aim of improving farm practices while ensuring sustainable development. This is reflected in a global demand for shrimp quality and a minimal impact on the environment . One of the key strategic priorities is to improve resistance to pathogenic bacteria causing outbreaks and economic losses, and probiotics offer a potential strategy to achieve this goal. Probiotics are defined as microorganisms exerting a beneficial effect by modulating microbiota when they are ingested in adequate quantity. They are good candidate to improve shrimp immune resistance, to reduce the use of antibiotic and lead to a more sustainable aquaculture. In this study, w e used probiotic strains which are native from the marine environment and are well adapted to the aquatic environment.
Material and methods
A 7-week water supplementation with or without marine probiotics was performed in 800-liter ponds on Litopenaeus vannamei PL12 in triplicate (n = 1000, water temperature = 28°C). This supplementation was continued during a 15- day challenge test with Vibrio parahaemolyticus causing AHPND in 40L ponds (n = 60, 3 replicates, water temperature = 28°C) . The capacity of the marine bacteria consortium on zootechnical parameters and shrimp survival rate was evaluated. A metabarcoding analysis was done on dead and alive shrimps to understand mechanisms involved at the microbiota level. Previously, an in vitro study was realiz ed to understand the antibiofilm and antibacterial potential of one of these marine probiotic strains on pathogenic V. harveyi ORM4. Three different biofilms were realized by testing the activity of the probiotic supernatant as a curative or preventive solution and with a co-inoculation with the pathogen. L iquid chromatography coupled with a mass spectrophotometer was also performed on probiotic supernatant to investigate the production of antibiofilm compounds
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Results
The results demonstrated a survival rate multiplied by 2.7 at the end of the challenge compared to the control group. The metabarcoding results showed that m arine probiotics, added to the water, had a positive impact on the shrimp larvae gut. Indeed, t he microbiota was marked by the presence of the Pseudoruegeria genus, known to be a defense mechanism against pathogens. This genus, coupled with marine probiotics, allowed shrimp larvae to have the therapeutic arsenal to fight the pathogen, explaining the better survival rate . The results show the ability of marine probiotics to influence the shrimp gut microbiota. Another characteristic of marine probiotics is their properties to have antibacterial and antibiofilm activity against pathogenic V. harveyi ORM4 when the probiotic is co-inoculated with the pathogen or used as a preventive or curative solution. We demonstrated in parallel the ability of this strain to synthesize lipopeptides which presented an antibiofilm activity against V. harveyi ORM4.
Conclusion
These studies demonstrated the ability of marine probiotics to limit the development of pathogens thanks to their antibacterial and antibiofilm activity but also to help shrimp larvae fight against stress caused by V. parahaemolyticus by modulating the microbiota and improving the survival rate.
Reference
Petit, C., Caudal, F., Taupin, L., Dufour, A., Le Ker, C., Giudicelli, F., Rodrigues, S., Bazire, A., 2024. Antibiofilm Activity of the Marine Probiotic Bacillus subtilis C3 Against the Aquaculture-Relevant Pathogen Vibrio harveyi. Probiotics Antimicrob. Proteins. https://doi.org/10.1007/s12602-024-10229-z