Carbon dioxide uptake and fixation by ferrous iron-oxidizing acidophilic bacteria

Abstract

CO2 is a major nutrient for autotrophic, mineral sulfide-oxidizing bacteria. The uptake and fixation of this carbon source is therefore critical for industrial mineral sulfide bioprocessing. The CO2 concentration influenced growth of five iron- or sulfur-oxidizing acidophiles to different extents. Those less affected by a growth-limiting CO2 concentration included Acidithiobacillus ferrooxidans and Acidithiomicrobium ferrooxidans. Acidithiobacillus ferrooxidans showed efficient uptake of 14CO2 from its concentration in air when previously grown under air while the maximum rate of CO2 uptake by cells previously grown under an enhanced CO2 concentration was only approached when the CO2 was increased to 0.1% v/v in air. In contrast, growth of Sulfobacillus thermosulfidooxidans was more adversely affected by limiting CO2 under air and the CO2 uptake rate was the same in cells grown with limiting or excess CO2. At. ferrooxidans also appeared to fix accumulated CO2 more efficiently than S. thermosulfidooxidans and RT-qPCR confirmed that adaptation of At. ferrooxidans to growth under limiting CO2 included production of form 1A ribulose bis-phosphate carboxylase in place of the form 1Aq enzyme which was predominant during growth under an enhanced CO2 concentration.