Quantitative proteomics insights into the response mechanisms of Aeromonas hydrophila to chromium stress

Aeromonas hydrophila, an opportunistic pathogen of aquatic fish, can survive under various environmental stresses, including exposure to chromium (Cr), a heavy metal that exerts dose-dependent toxic effects on bacteria. Elucidating the mechanism underlying its response to chromium stress holds considerable significance, while related studies are still scarce. In this study, growth curve experiments showed that potassium dichromate inhibited bacterial growth in a concentration-dependent manner. The concentration of 0.15 mg/mL, which induces significant but non-lethal growth inhibition, was selected to probe the proteomic response under growth-inhibitory stress. Quantitative proteomics analysis identified 678 altered proteins under chromium stress with 294 proteins increased and 384 decreased abundances. Functional enrichment analyses revealed that chromium mainly suppressed pathways like energy metabolism, amino acid metabolism, and bacterial chemotaxis, while activating defense mechanisms such as DNA repair and siderophore transport. RT-qPCR analysis confirmed the transcriptional upregulation of several siderophore transport-related genes and one DNA repair-related gene, supporting the trend observed in proteomics analysis. Further analysis showed antioxidants including epicatechin, ascorbic acid and gallic acid alleviated chromium toxicity, suggesting that reactive oxygen species (ROS) play an important role in chromium stress. Additionally, deletion of AHA_2968, encoding a GGDEF-domain protein, markedly enhanced the sensitivity of A. hydrophila to chromium, suggesting that c-di-GMP signaling may be involved in the response to chromium stress. In summary, our findings provide novel insights into the molecular responses of A. hydrophila to growth-inhibitory chromium stress.