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PHOTOSYNTHETIC INORGANIC CARBON ACQUISITION IN AN ACID‐TOLERANT, FREE‐LIVING SPECIES OF COCCOMYXA (CHLOROPHYTA) 1
Author(s) -
Verma Vidhu,
Bhatti Shabana,
Huss Volker A. R.,
Colman Brian
Publication year - 2009
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.2009.00718.x
Subject(s) - photosynthesis , biology , bicarbonate , chlorophyta , total inorganic carbon , carbonic anhydrase , dcmu , botany , biophysics , carbon dioxide , algae , biochemistry , enzyme , ecology , photosystem ii , endocrinology
The processes of CO 2 acquisition were characterized for the acid‐tolerant, free‐living chlorophyte alga, CPCC 508. rDNA data indicate an affiliation to the genus Coccomyxa , but distinct from other known members of the genus. The alga grows over a wide range of pH from 3.0 to 9.0. External carbonic anhydrase (CA) was detected in cells grown above pH 5, with the activity increasing marginally from pH 7 to 9, but most of the CA activity was internal. The capacity for HCO 3 − uptake of cells treated with the CA inhibitor acetazolamide (AZA), was investigated by comparing the calculated rate of uncatalyzed CO 2 formation with the rate of photosynthesis. Active bicarbonate transport occurred in cells grown in media above pH 7.0. Monitoring CO 2 uptake and O 2 evolution by membrane‐inlet mass spectrometry demonstrated that air‐grown cells reduced the CO 2 concentration in the medium to an equilibrium concentration of 15 μM, but AZA‐treated cells caused a drop in extracellular CO 2 concentration to a compensation concentration of 27 μM at pH 8.0. CO 2 ‐pulsing experiments with cells in the light indicated that the cells do not actively take up CO 2 . An internal pool of unfixed inorganic carbon was not detected at the CO 2 compensation concentration, probably because of the lack of active CO 2 uptake, but was detectable at times before compensation point was reached. These results indicate that this free‐living Coccomyxa possesses a CO 2 ‐concentrating mechanism (CCM) due to an active bicarbonate‐uptake system, unlike the Coccomyxa sp. occurring in symbiotic association with lichens.