Characterization of two TonB systems in marine fish pathogen Vibrio alginolyticus : their roles in iron utilization and
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S H O R T CO M MU N I C A T I O N
Characterization of two TonB systems in marine Wsh pathogen Vibrio alginolyticus: their roles in iron utilization and virulence Qiyao Wang · Qin Liu · Xiaodan Cao · Minjun Yang · Yuanxing Zhang
Received: 7 May 2008 / Revised: 22 June 2008 / Accepted: 30 June 2008 / Published online: 16 July 2008 © Springer-Verlag 2008
Abstract In Gram-negative bacteria, the TonB/ExbB/ ExbD complex is required to energize the speciWc highaYnity receptors mediating iron uptake processes. In Wsh pathogen Vibrio alginolyticus MVP01, which exhibited capacities to scavenge iron sources with various speciWc iron uptake systems, we identiWed and characterized two sets of TonB systems. In V. alginolyticus, TonB1 and TonB2 systems were arrayed as TonB1–ExbB1–ExbD1 and ExbB2–ExbD2–TonB2, respectively. The transcription of the TonB systems was regulated by the iron concentration in culture medium. While TonB1 system speciWcally contributed to the hemin and hemoglobin utilization in V. alginolyticus MVP01, both of the TonB systems showed abilities to support the utilization of iron sources from ferrichrome and vibrioferrin, the endogenous siderophore of V. alginolyticus. In addition, when mutants of the TonB systems were inoculated intraperitoneally into the Wsh Brachydanio rerio, marked attenuation in virulence of V. alginolyticus was observed, indicating that both of the TonB systems are essential for the virulence of V. alginolyticus. Keywords Iron transportation · TonB system · Vibrio alginolyticus · Virulence
Communicated by Erko Stackebrandt. Q. Wang · Q. Liu · X. Cao · M. Yang · Y. Zhang (&) State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai 200237, People’s Republic of China e-mail: [email protected]
Introduction Iron is virtually essential for most bacteria. Although iron exists as one of the most abundant element in the earth, the fact that it is prone to be oxidized into insoluble iron complexes makes it not readily available to organisms in the natural milieu, e.g. sea water. In bacteria, exquisite mechanisms have been developed for acquisition of diVerent kind of iron sources, among which is generation and assimilation of siderophore, small molecules highly aYnitive to ferric iron. In Gram-negative bacterium, multiple membranelocalized receptors speciWcally recognize the iron-containing complexes such as ferric-siderophore molecules, heme and so on, and then transport them into the cell in an energy-dependent manner to meet the needs of numerous cellular processes (Braun and Braun 2002). Usually the iron acquisition process is controlled by ferric uptake regulation protein (Fur) and the concentration of bio-available iron to keep the intracellular iron at a relative steady level for the optimal growth (Escolar et al. 1999). TonB–ExbB–ExbD complex is required to energize the process of transmembrane transportation of a wide variety of iron loaded ligands or other organometallic compounds, such as vitamin B12 (Byron et al. 2007). Furthermor
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