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Inorganic carbon acquisition in the acid‐tolerant alga Chlorella kessleri
Author(s) -
ElAnsari Omar,
Colman Brian
Publication year - 2015
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/ppl.12228
Subject(s) - total inorganic carbon , bicarbonate , photosynthesis , intracellular ph , chemistry , chlorella , algae , carbon dioxide , botany , environmental chemistry , biochemistry , intracellular , biology , organic chemistry
The ability of the freshwater alga, Chlorella kessleri , to maintain a carbon concentrating mechanism when grown at acid pH was investigated. The alga grows over the pH range 4.0–9.0 and was found to take up bicarbonate and CO 2 actively when grown at pH 6.0. However, when grown at acid pH (below 5.5), it does not have active CO 2 uptake. The acidotolerant species maintained an internal pH of 6.1–7.5 over the external pH range 4.5–7.5, thus the pH difference between the cell interior and the external medium was large enough to allow for the diffusive uptake of CO 2 at acid external pH . Mass spectrometric monitoring of O 2 and CO 2 fluxes by suspensions of C. kessleri , grown at acid pH , and maintained at pH 7.5 showed that the rates of O 2 evolution did not exceed those of CO 2 uptake. The final CO 2 compensation concentrations of 14.0–17.7 µ M reached by photosynthetic cells were above the CO 2 equilibrium concentration in the external medium, indicating a lack of active CO 2 uptake at acid pH . Chlorella kessleri accumulated CO 2 with internal concentrations that were 9.9, 18.7 and 22.7‐fold that of the external medium for cells grown, respectively, at pH 4.5, 5.0 and 5.5. The ability of C. kessleri cells to accumulate high intracellular concentrations of inorganic carbon at acid pH would provide a sufficiently high concentration of CO 2 at the active site of Rubisco thus allowing the alga to maintain growth rates similar to those at alkaline pH .