Enrichment isolation and metabolic characteristics of <i>Halobacteriovorax</i> , cosmopolitan obligate predators in marine conditions

<i>Bdellovibrionota,</i> 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 <i>Halobacteriovorax</i> 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 (<i>Vibrionaceae</i>/<i>Alteromonadales</i>), optimal at 10² predator:prey ratios. In simulated seawater, isolates achieved a 3-log reduction of <i>Vibrio alginolyticus</i> within 10 hours, highlighting potent biocontrol utility. This work bridges cultivability gaps via ecological strategies, advancing evolutionary insights into predation mechanisms while positioning <i>Bdellovibrionota</i> as precision biocontrol agents for sustainable aquaculture disease management.IMPORTANCEThis study resolves the paradox of <i>Bdellovibrionota</i>'s ubiquitous genomic presence versus cultivability scarcity by developing a prey-driven enrichment strategy that isolates 33 marine <i>Halobacteriovorax</i>. 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, <i>Halobacteriovorax</i> achieves rapid biocontrol, reducing the aquaculture pathogen <i>Vibrio alginolyticus</i> by 3 log within 10 hours under marine conditions, outperforming phages in oligotrophic environments. <i>Bdellovibrionota</i> 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.