Low pH rather than high CO₂ concentration itself inhibits growth of Arthrospira

Microalga is a promising candidate for bio-mitigation of CO₂. It has been longtime recognized that high CO₂ concentration would impose stresses on microalga to suppress the growth. However, this concept was challenged in this research by investigating the growth, photosynthesis and anti-oxidant characteristics of Arthrospira platensis under independent effects of CO₂ concentrations and pH. Results showed the growth of A. platensis was only inhibited when broth was in acidic pH. Microalgal cells could deal with high CO₂ concentration readily if medium pH was maintained in favorite level. Photosynthesis was inhibited swiftly and significantly under acidified condition. The singlet oxygen was produced in low level for alkalic pH treatment, however it burst quickly after low pH stress was imposed. Accordingly, it was proposed that the phenomena of high CO₂ intolerance was caused by CO₂ induced pH decline rather than high CO₂ concentration itself. This finding has significance on large scale application of microalga based CO₂ mitigation and flue gas treatment since it proved concentrated CO₂ could be directly assimilated without dilution.