CO₂ fixation stability by Sulfurovum lithotrophicum 42BKT^T depending on pH and ionic strength conditions

The dissolution of CO₂, a greenhouse gas most responsible for global warming, in seawater lowers its pH and increases its ionic strength. Sulfurovum lithotrophicum 42BKT^T, a deep-sea chemolithotrophic bacterium, can fix high concentration CO₂. In this study, we investigated the effect of pH and ionic strength variation of seawater on CO₂ fixation by this bacterium. For a stable and continuous fixation of high concentration CO₂ by S. lithotrophicum 42BKT^T, the pH and ionic strength of the seawater-based medium should be 6.1–6.8 and <0.8 M, respectively. The deviation of pH and ionic strength from these ranges was indicated by the appearance of lengthened and fattened cells whose length and diameter increased by 70–90%. These results imply that the harmful effect of dissolved CO₂ on marine ecosystem is due to the increase in ionic strength and decrease in pH of seawater.