Abstract
<jats:p> Nitrogen availability is a key factor shaping microbial metabolism, ecological adaptation, and nitrogen cycling in aquatic environments. Members of the genus <jats:italic>Vibrio</jats:italic> are ubiquitous heterotrophic bacteria in marine and aquaculture ecosystems, yet their responses to different inorganic nitrogen sources remain poorly understood. Here, we systematically compared the growth characteristics, nitrogen transformation capacity, and molecular responses of Vibrio harveyi and <jats:italic>Vibrio parahaemolyticus</jats:italic> under ammonium (NH <jats:sub>4</jats:sub> <jats:sup>+</jats:sup> ), nitrate (NO <jats:sub>3</jats:sub> <jats:sup>−</jats:sup> ), and nitrite (NO <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> ) conditions using physiological assays, comparative genomic analysis, and transcriptomic profiling. <jats:italic>V. harveyi</jats:italic> exhibited broader nitrogen utilization capacity and was able to grow under all three nitrogen conditions, whereas <jats:italic>V. parahaemolyticus</jats:italic> showed a strong preference for NH <jats:sub>4</jats:sub> <jats:sup>+</jats:sup> and limited growth under NO <jats:sub>3</jats:sub> <jats:sup>−</jats:sup> and NO <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> conditions. Moreover, <jats:italic>V. harveyi</jats:italic> displayed rapid population expansion accompanied by reduced long-term viability, while <jats:italic>V. parahaemolyticus</jats:italic> maintained greater population stability. Both species showed NO <jats:sub>3</jats:sub> <jats:sup>−</jats:sup> accumulation during growth despite lacking canonical nitrification genes under NH <jats:sub>4</jats:sub> <jats:sup>+</jats:sup> condition, suggesting the potential involvement of non-canonical heterotrophic nitrification processes. Transcriptomic analysis revealed nitrogen source-dependent metabolic specialization in <jats:italic>V. harveyi</jats:italic> . NH <jats:sub>4</jats:sub> <jats:sup>+</jats:sup> availability promoted motility-associated responses and metabolic overflow, whereas NO <jats:sub>3</jats:sub> <jats:sup>−</jats:sup> induced iron acquisition-related pathways and NO <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> activated assimilatory nitrite reduction coupled with oxidative stress adaptation. These findings demonstrate that inorganic nitrogen availability drives divergent metabolic and adaptive strategies in <jats:italic>Vibrio</jats:italic> , providing new insights into their nitrogen metabolic potential and ecological roles in aquatic environments. </jats:p>