Isolation and characterization of a novel biomineral stalk-forming iron-oxidizing bacterium from a circumneutral groundwater seep

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SummaryThe Fe-depositing microorganismGallionella ferrugineawas first described in 1836 based on its association with Fe-rich environments and its distinctive morphology. Since then, this morphology has been widely used to identifyG. ferruginea. Researchers have isolated several Fe-oxidizing bacteria (FeOB) related toGallionella; however, few isolates have produced organized extracellular biomineral structures, and of these, only one stalk former has a sequenced 16S rRNA gene, listed asG. ferrugineain the GenBank database. Here we report the isolation and characterization of a novel stalk-forming Fe-oxidizing bacterium, strain R-1, from a freshwater Fe seep. Despite a strong morphological similarity toG. ferruginea, this isolate has only 93.55% 16S rRNA gene sequence similarity with the previously determined sequence. R-1 only grows on Fe(II) substrates, at pH 5.6 to 7.0 and from 10°C to 35°C, with a doubling time of ˜15 h at pH 6.3 and 22°C. It is aBetaproteobacterium, most closely related to uncultured bacteria from microaerobic Fe(II)-rich groundwater springs. The most closely related isolates areSideroxydansspp. (94.05–94.42% sequence similarity), FeOB that are not known to produce morphologically distinct minerals. To our knowledge, this is the first reported stalk-forming freshwater FeOB isolate distinct fromGallionella.

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