Enrichment isolation and metabolic characteristics of Halobacteriovorax, cosmopolitan obligate predators in marine conditions.

Bdellovibrionota, ubiquitous obligate predators regulating microbial ecosystems, suffer from cultivability limitations with only 12 known isolates despite >1,120 genomes. We developed a prey-addition enrichment system and isolated 33 marine Halobacteriovorax strains from sediments that fall into four species, three of which are candidate novel species. Genomic analyses revealed streamlined metabolism with auxotrophy for amino acid/hypoxanthine synthesis, enhanced chemotaxis, and specialized carbohydrate-active enzymes (e.g., GH23 hydrolases), defining adaptations for obligate predation. Predation assays demonstrated broad activity against aquaculture pathogens (Vibrionaceae/Alteromonadales), optimal at 10² predator:prey ratios. In simulated seawater, isolates achieved a 3-log reduction of Vibrio alginolyticus within 10 hours, highlighting potent biocontrol utility. This work bridges cultivability gaps via ecological strategies, advancing evolutionary insights into predation mechanisms while positioning Bdellovibrionota as precision biocontrol agents for sustainable aquaculture disease management.IMPORTANCEThis study resolves the paradox of Bdellovibrionota's ubiquitous genomic presence versus cultivability scarcity by developing a prey-driven enrichment strategy that isolates 33 marine Halobacteriovorax. Their streamlined genomes unveil obligate predation adaptations: auxotrophy for amino acid/hypoxanthine synthesis, enhanced chemotaxis systems, and GH23 peptidoglycan hydrolases, illuminating evolutionary trajectories distinct from other predators. Crucially, Halobacteriovorax achieves rapid biocontrol, reducing the aquaculture pathogen Vibrio alginolyticus by 3 log within 10 hours under marine conditions, outperforming phages in oligotrophic environments. Bdellovibrionota shapes the environment by regulating microbial community structures and maintaining ecological balance in ecosystems. Additionally, they hold great promise for being developed as biological agents to replace antibiotics, offering a viable solution for the prevention and control of vibrio diseases in marine aquaculture.