Isolation and characterisation of mineral-oxidising Acidibacillus spp. from mine sites and geothermal environments in different global locations

Eight strains of acidophilic bacteria, isolated from mine-impacted and geothermal sites from different parts of the world, were shown to form a distinct Glade (proposed genus Acidibacillus) within the phylum Firmicutes, well separated from the acidophilic genera Sulfobacillus and Alicyclobacillus. Two of the strains (both isolated from sites in Yellowstone National Park, USA) were moderate thermophiles that oxidised both ferrous iron and elemental sulphur, while the other six were mesophiles that also oxidised ferrous iron, but not sulphur. All eight isolates reduced ferric iron to varying degrees. The two groups shared <95% similarity of their 16S rRNA genes and were therefore considered to be distinct species: Acidibacillus sulfuroxidans (moderately thermophilic isolates) and Acidibacillus ferrooxidatzs (mesophilic isolates). Both species were obligate heterotrophs; none of the eight strains grew in the absence of organic carbon. Acidibacillus spp. were generally highly tolerant of elevated concentrations of cationic transition metals, though A. sulfitroxidans strains were more sensitive to some (e.g. nickel and zinc) than those of A. ferrooxidans. Initial annotation of the genomes of two strains of A. ferrooxidans revealed the presence of genes (cbbL) involved in the RuBisCO pathway for CO2 assimilation and iron oxidation (rus), though with relatively low sequence identities. (C) 2016 Published by Elsevier Masson SAS on behalf of Institut Pasteur.