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

Bdellovibrionota play crucial ecological roles in regulating microbial populations and nutrient cycling through obligate predation. They are globally ubiquitous, distributed across aquatic, terrestrial, and host-associated ecosystems, and have over 1,120 genome sequences available. However, their physiological and metabolic characterization remains poorly understood due to the cultivability challenge, with only 12 isolated species reported. Here, we developed a prey bacteria addition-based enrichment culture system and isolated 33 Bdellovibrionota strains from marine sediments. They represent three novel species in the genus Halobacteriovorax, for which the names Halobacteriovorax aquimaris, Halobacteriovorax mangrovi, Halobacteriovorax exovorus are proposed. These isolates contain streamlined genomes with metabolic deficiencies of amino acid and hypoxanthine nucleotide synthesis pathways. Comparative genomic analyses further exhibited the enhanced chemotaxis and specialized CAZyme profiles in contrast to other non-obligate predators, suggesting their unique adaptive mechanisms for obligate predation lifestyles. Predation experiments demonstrated a wide prey spectrum targeting aquatic pathogens Vibrionaceae and Alteromonadales, with optimal predation at 10² predator: prey ratios. A high predation ratio to Vibrio alginolyticus was also observed in laboratory-simulated seawater conditions, highlighting its huge potential as biocontrol bacteria in aquaculture. By bridging cultivability gaps through ecological enrichment and multi-omics validation, this work not only advances understanding of Bdellovibrionota's evolutionary adaptations and ecological governance but also positions them as precision biocontrol agents against aquaculture pathogens, providing novel genetic tools for green biocontrol of aquaculture diseases.