A phosphoporin homolog plays a critical role in the dissimilatory iron-respiration linked to iron (III) reduction by a cold-adapted bacterium, Shewanella livingstonensis Ac10

抄録

Under anaerobic conditions, some bacteria use various metal compounds as terminal electron acceptors, and can thus obtain energy for their growth by respiration in the absence of oxygen. Molecular mechanism of anaerobic metal reduction by the mesophilic Shewanella and Geobacter strains, model organisms of bacterial dissimilatory metal reduction, has been well studied so far. In this study, we focused on the iron respiration by an Antarctic cold-adapted bacterium, Shewanella livingstonensis Ac10, which can grow at a temperature range of 0°C–25°C, and has a potential application in the biological reduction of metal contaminants under cold environments. In the presence of iron (III) citrate, S. livingstonensis Ac10 inducibly produced an outer membrane phosphoporin homolog, PhoE, but not in the fumarate-containing medium. By western blotting and real-time RT-PCR analyses, it was confirmed that the production of PhoE was dependent on the presence of iron (III) citrate, and the expression of phoE was regulated at the transcriptional level. When the gene coding for PhoE in S. livingstonensis Ac10 was disrupted, the cell proliferation and iron (II) ion (Fe²⁺) production by the mutant strain grown in the presence of iron (III) citrate was significantly reduced than that by the wild-type strain. Introduction of an expression vector for phoE into the phoE-disrupted mutant restored the growth defect of the mutant, revealing that a phosphoporin homolog plays a critical role in the dissimilatory iron reduction by S. livingstonensis Ac10.