Dissolved inorganic carbon concentration mechanism in Chlamydomonas moewusii

The dissolved inorganic carbon concentrating mechanism(s) of Chlamydomonas moewusii CC 55 was compared with C. reinhardtii strain 137. C. moewusii is similar to C. reinhardtii with respect to maximal rates of photosynthetic oxygen evolution, CO2 fixation, respiration, and the ability to efficiently concentrate inorganic carbon. C. moewusii has a low, but measurable amount of external carbonic anhydrase (CA) that was not inhibited by acetazolamide (AZ), an inhibitor of periplasmic carbonic anhydrase (pCA) in C. reinhardtii. The K0.5(CO2) for air-grown C. moewusii is about 1 μM and the algal cells accumulated dissolved inorganic carbon (DIC) to a level of about 1 mM in 60 s. AZ did not inhibit CO2 fixation and the DIC accumulation by air-grown cells of C. moewusii. The K0.5(CO2) for both species remains constant from pH 6.5 to 9.5 while K0.5(HCO3-) increased logarithmically, which indicates that CO2 is the apparent inorganic carbon species that enters the cells in both algae. Antiserum prepared against the 37 kDa peptide of pCA from C. reinhardtii was immunoreactive with polypeptides of 26, 28, and 32 kDa in C. moewusii. The periplasmic carbonic anhydrase (pCA) activity is a part of the dissolved inorganic carbon concentrating mechanism in C. reinhardtii, but C  moewusii accomplished inorganic carbon accumulation without an AZ-sensitive pCA.