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

Summary The Fe‐depositing microorganism Gallionella ferruginea was 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 identify G. ferruginea . Researchers have isolated several Fe‐oxidizing bacteria (FeOB) related to Gallionella ; however, few isolates have produced organized extracellular biomineral structures, and of these, only one stalk former has a sequenced 16S rRNA gene, listed as G. ferruginea in 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 to G. 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 a Betaproteobacterium , most closely related to uncultured bacteria from microaerobic Fe(II)‐rich groundwater springs. The most closely related isolates are Sideroxydans spp. (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 from Gallionella .