Preliminary Investigation of Iron Acquisition in Hypervirulent Klebsiella pneumoniae Mediated by Outer Membrane Vesicles

OBJECTIVE: To investigate the role of outer membrane vesicles (OMVs) and related proteins in iron acquisition of hypervirulent Klebsiella pneumoniae (HVKP) and classic Klebsiella pneumoniae (cKP). METHODS: The OMVs of HVKP and cKP under iron-deficient and iron-sufficient media were extracted and purified by ultracentrifugation. Transmission electron microscopy (TEM) was used to identify OMVs. The quantitative proteomics were performed based on mass spectrometry. RESULTS: Four OMVs samples secreted by HVKP and cKP under iron-deficient and iron-sufficient environment were isolated and collected (HVKP OMVs under iron-deficient environment (A1), HVKP OMVs under iron-sufficient environment (A2), cKP OMVs under iron-deficient environment (B1), cKP OMVs under iron-sufficient environment (B2)). The amount of OMVs released by HVKP in iron-deficient medium was significantly larger than that in iron-sufficient medium (P < 0.05). HVKP secreted more OMVs than cKP in iron-deficient medium (P < 0.05). A total of 1074 kinds of proteins were identified in four samples. A comparison between the iron-deficient vs iron-sufficient environment showed that 61 proteins in HVKP OMVs were identified with a significant change in abundance under iron-deficient environment. Among them, 17 proteins were related to iron acquisition and transportation systems. While in cKP OMVs, 62 proteins significantly changed under iron-deficient environment in which 5 proteins were related to iron acquisition and transportation systems. Upon comparison of the HVKP vs cKP OMVs under iron deficiency, 81 proteins were detected with a significant change in which 8 proteins were related to iron acquisition and transportation systems. CONCLUSION: Above all, the results of this study suggest a potential role for OMVs in iron acquisition of HVKP and provide evidence of potential connections between OMVs and strong iron-acquisition ability of HVKP during iron limitation.