Characterization of marine probiotic bacteria for biocontrol of pathogenic Vibrio spp. in aquaculture systems

Project Abstract

The rise of antibiotic resistance and environmental concerns associated with chemical therapeutics necessitate the exploration of sustainable alternatives for disease control in aquaculture. This study investigates marine-derived probiotic bacteria for biocontrol of pathogenic Vibrio species, with a focus on isolation, characterization, antagonistic activity, and mechanism of action against Vibrio ordalii, Vibrio vulnificus, and Vibrio parahaemolyticus. A curated collection of 240 marine bacterial isolates was obtained from coastal seawater, sediment, and marine biofilms, followed by primary screening for antagonism using cross-streak and spot-on-lawn assays against the target Vibrio pathogens. The most promising strains were identified by 16S rRNA gene sequencing and phylogenetic analysis, revealing predominance of Bacillus spp., Pseudoalteromonas spp., and Vibrio-associated competitors with broad-spectrum inhibitory effects. Secondary screening employed dual-culture assays, cell-free supernatants, and co-culture systems to quantify inhibition zones, growth suppression, and changes in Vibrio viability under varying salinity (10–35 ppt), temperature (20–30°C), and pH (6.5–8.5) regimes that simulate aquaculture nursery conditions. Mechanistic investigations included assessment of (i) production of antibacterial compounds (bacteriocins, lipopeptides, siderophores) via biochemical assays and mass spectrometry, (ii) competition for essential nutrients and niche occupation through metabolic profiling and carbon source utilization, and (iii) quorum sensing disruption using biosensor strains to evaluate interference with Vibrio virulence regulation. Genomic analyses using whole-genome sequencing of top-performing strains identified gene clusters responsible for antimicrobial biosynthesis, iron acquisition, and stress tolerance, providing insights into the safety and functional capacity of potential probiotic candidates. In vitro findings were complemented by a simulated aquaculture tank trial, where probiotic consortia were introduced prior to pathogen challenge. Water quality parameters (ammonia, nitrite, nitrate, pH, dissolved oxygen) were monitored, alongside microbial community dynamics via 16S rRNA amplicon sequencing, to evaluate stability and colonization efficiency of probiotics and suppression of Vibrio blooms. Results demonstrate that selected marine isolates exhibit significant inhibitory effects against all tested Vibrio spp., including reductions in pathogenic counts by up to 3–4 log units in co-culture and tank experiments. Mechanisms appear multifactorial, combining bacteriocin-like compound activity, competitive exclusion, and disruption of Vibrio quorum sensing, with enhanced efficacy observed under moderate salinity and temperature conditions typical of coastal aquaculture. Additionally, probiotic treatments modulated the microbial community structure by enriching beneficial native taxa and reducing virulent Vibrio-associated OTUs, without detectable horizontal gene transfer of deleterious traits. The study also evaluates safety parameters, including absence of hemolytic activity, non-pathogenicity in Galleria mellonella models, and preliminary environmental risk assessment indicating minimal persistence beyond intended application windows. Collectively, the research establishes marine probiotic strains as promising biocontrol agents capable of mitigating Vibrio-related diseases in aquaculture while promoting sustainable production and reducing reliance on antibiotics. The findings provide a framework for the development of commercial probiotic formulations, standardized screening pipelines, and guidelines for deployment, monitoring, and regulatory compliance in diverse aquaculture systems.

Project Overview

What This Project Is About

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A straightforward study that looks at beneficial marine bacteria and how they can help reduce disease-causing Vibrio bacteria in fish farms. It asks whether certain probiotic strains can lower harmful Vibrio levels and support healthier aquaculture systems.

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The Problem It Addresses

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Vibrio bacteria can cause disease in seafood and lead to economic losses for farmers. Relying on antibiotics is not ideal due to resistance and environmental concerns. This project explores natural, living helpers from the marine environment to keep Vibrio in check.

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Objectives of the Project

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1. Identify marine bacteria that show potential against Vibrio in lab tests.
2. Evaluate safety and basic characteristics of selected probiotic candidates.
3. Measure how well the probiotics reduce Vibrio growth in controlled setups.
4. Suggest practical ways to apply probiotics in real aquaculture settings.

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What You Will Do Step by Step

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1) Review simple background information on probiotics and Vibrio. 2) Collect and culture marine bacterial samples. 3) Screen candidates for anti-Vibrio activity using basic lab assays. 4) Test safety and preliminary suitability for aquaculture. 5) Analyze results to identify the strongest probiotic candidates. 6) Compare outcomes under different conditions that mimic farming environments. 7) Summarize practical considerations for implementation.

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Expected Outcome

Identification of one or more safe marine probiotic strains that can suppress pathogenic Vibrio in lab-like aquaculture conditions, along with practical recommendations for application and potential limitations or further testing needs.