Isolation and characterization of an organics-sensitive iron-oxidizing acidophile affiliated with the genus Acidithiobacillus. Acidithiobacillus sp. NU-1

The genus Acidithiobacillus includes iron-oxidizing lithoautotrophic acidophiles that thrive in acidic mine environments. A. ferrooxidans is a representative species and has been extensively studied for its relevance to bioleaching of precious metals. In our attempts to cultivate the type strain of A. ferrooxidans (strain ATCC 23270), repeated transfers to fresh inorganic iron media resulted in the emergence of cultures with improved growth traits. Strains were isolated from the resultant cultures by forming colonies on inorganic silica-gel plates. A representative isolate (strain NU-1) is unable to form colonies on agarose plates and much more sensitive to organics, such as glucose, than the type strain. Strain NU-1 exhibits superior growth capacity in inorganic media compared to other iron-oxidizing acidithiobacilli, suggesting its potential in bioleaching applications. A draft genome uncovers unique genomic features of strain NU-1, indicating that this strain is not a simple mutant of A. ferrooxidans. We suggest that the use of inorganic silica-gel plates facilitates the isolation of as-yet-uncultivated lithoautotrophic acidophiles from environmental samples and enrichment cultures.