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Ferrimicrobium acidiphilum gen. nov., sp. nov. and Ferrithrix thermotolerans gen. nov., sp. nov.: heterotrophic, iron-oxidizing, extremely acidophilic actinobacteria

D. Barrie Johnson, Paula Bacelar-Nicolau, Naoko Okibe, Angharad Thomas and Kevin B. Hallberg

School of Biological Sciences, College of Natural Sciences, Bangor University, Bangor LL57 2UW, UK

Correspondence
D. Barrie Johnson
d.b.johnson{at}bangor.ac.uk

Two novel extremely acidophilic, iron-oxidizing actinobacteria were isolated, one from a mine site in North Wales, UK (isolate T23^T), and the other from a geothermal site in Yellowstone National Park, Wyoming, USA (Y005^T). These new actinobacteria belong to the subclass Acidimicrobidae, and in contrast to the only other classified member of the subclass (Acidimicrobium ferrooxidans), both isolates were obligate heterotrophs. The mine site isolate was mesophilic and grew as small rods, while the Yellowstone isolate was a moderate thermophile and grew as long filaments, forming macroscopic flocs in liquid media. Both isolates accelerated the oxidative dissolution of pyrite in yeast extract-amended cultures, but neither was able to oxidize reduced forms of sulfur. Ferrous iron oxidation enhanced growth yields of the novel mesophilic actinobacterium T23^T, though this was not confirmed for the Yellowstone isolate. Both isolates catalysed the dissimilatory reduction of ferric iron, using glycerol as electron donor, in oxygen-free medium. Based on comparative analyses of base compositions of their chromosomal DNA and of their 16S rRNA gene sequences, the isolates are both distinct from each other and from Acidimicrobium ferrooxidans, and are representatives of two novel genera. The names Ferrimicrobium acidiphilum gen. nov., sp. nov. and Ferrithrix thermotolerans gen. nov., sp. nov. are proposed for the mesophilic and moderately thermophilic isolates, respectively, with the respective type strains T23^T (=DSM 19497^T=ATCC BAA-1647^T) and Y005^T (=DSM 19514^T=ATCC BAA-1645^T).

Present address: Universidade Aberta, 1269-001-Lisboa, Portugal.

Present address: Research Institute for Innovative Technology for the Earth (RITE), Kyoto, Japan.

The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of Ferrimicrobium acidiphilum and Ferrithrix thermotolerans are AF251436 and AY140237, respectively.

Supplementary figures showing pyrite oxidation and reduction of ferric iron by isolates T23^T and Y005^T are available with the online version of this paper.