TY  - JOUR
A1  - Spijkerman, Elly
A1  - Stojkovic, Slobodanka
A1  - Beardall, John
T1  - CO2 acquisition in Chlamydomonas acidophila is influenced mainly by CO2, not phosphorus, availability
JF  - Photosynthesis research
N2  - The extremophilic green microalga Chlamydomonas acidophila grows in very acidic waters (pH 2.3-3.4), where CO2 is the sole inorganic carbon source. Previous work has revealed that the species can accumulate inorganic carbon (Ci) and exhibits high affinity CO2 utilization under low-CO2 (air-equilibrium) conditions, similar to organisms with an active CO2 concentrating mechanism (CCM), whereas both processes are down-regulated under high CO2 (4.5 % CO2) conditions. Responses of this species to phosphorus (Pi)-limited conditions suggested a contrasting regulation of the CCM characteristics. Therefore, we measured external carbonic anhydrase (CA(ext)) activities and protein expression (CAH1), the internal pH, Ci accumulation, and CO2-utilization in cells adapted to high or low CO2 under Pi-replete and Pi-limited conditions. Results reveal that C. acidophila expressed CA(ext) activity and expressed a protein cross-reacting with CAH1 (the CA(ext) from Chlamydomonas reinhardtii). Although the function of this CA remains unclear, CA(ext) activity and high affinity CO2 utilization were the highest under low CO2 conditions. C. acidophila accumulated Ci and expressed the CAH1 protein under all conditions tested, and C. reinhardtii also contained substantial amounts of CAH1 protein under Pi-limitation. In conclusion, Ci utilization is optimized in C. acidophila under ecologically relevant conditions, which may enable optimal survival in its extreme Ci- and Pi-limited habitat. The exact physiological and biochemical acclimation remains to be further studied.
KW  - CO2 concentrating mechanism
KW  - Inorganic phosphorus limitation
KW  - Varying CO2 condition
KW  - Extremophilic green alga
KW  - Co-limitation
KW  - Internal pH
KW  - Inorganic carbon accumulation
KW  - Affinity for CO2 uptake
Y1  - 2014
U6  - https://doi.org/10.1007/s11120-014-0016-6
SN  - 0166-8595
SN  - 1573-5079
VL  - 121
IS  - 2-3
SP  - 213
EP  - 221
PB  - Springer
CY  - Dordrecht
ER  -