THE POTENTIAL FOR DIAZOTROPHY IN IRON-OXIDIZING AND SULFUR-OXIDIZING ACIDOPHILIC BACTERIA

Acetylene reduction was observed with ferrous-iron-oxidizing Thiobacil lus ferrooxidans, as expected from previous studies with this bacteriu m. Acetylene reduction was also found during the growth of T. ferrooxi dans on tetrathionate. Only Leptospirillum ferrooxidans, one of severa l other phylogenetically diverse, ferrous-iron- and/or sulfur-oxidizin g acidophilic microorganisms, also reduced acetylene. A reduction of t he oxygen concentration in the culture atmosphere was necessary to all eviate inhibition of nitrogenase activity. DNA sequences homologous to nif structural genes were found in both organisms. Diazotrophic growt h of L. ferrooxidans was inferred from an increase in iron oxidation i n ammonium-free medium when the oxygen concentration was limited and f rom apparent inhibition by acetylene under these conditions.