Quantitative Proteomics Reveals the Adaptive Mechanisms of <i>Aeromonas hydrophila</i> Under Cobalt Stress

Cobalt is an essential micronutrient but becomes toxic at elevated concentrations, requiring microorganisms to balance acquisition and detoxification. Aeromonas hydrophila, an opportunistic aquatic pathogen, is often encountered in metal-contaminated aquatic environments; however, its adaptive responses to cobalt stress have not been systematically characterized. Here, we applied quantitative proteomics to characterize the global protein response of A. hydrophila under cobalt stress. A total of 2767 proteins were identified, of which 724 were differentially abundant. Enrichment analyses indicated that cobalt exposure was associated with alterations in energy metabolism, oxidative phosphorylation, and ribosome-related pathways. Gene set enrichment analysis suggested an overall upregulation of ribosome-associated functions, accompanied by down regulation of carbon metabolism and the tricarboxylic acid cycle. Protein-protein interaction network mapping identified 15 functional clusters, with core modules linked to oxidative phosphorylation, ABC transport, carbohydrate metabolism, and Fe-S cluster biogenesis. Ten hub proteins associated with respiratory and transport systems were identified based on network topology. Functional validation using seven deletion mutants indicated that genes encoding shikimate kinase, glutaminase, and arsenate reductase contribute to cobalt tolerance. Together, these findings provide a systems-level view of how A. hydrophila adapts to cobalt stress, reveal candidate factors mediating metal resistance, and suggest potential targets for antimicrobial development and bioremediation strategies.