Premium
Photosynthesis and inorganic carbon acquisition in the cyanobacterium Chlorogloeopsis sp. ATCC 27193
Author(s) -
Skleryk Robert S.,
Tyrrell Pascal N.,
Espie George S.
Publication year - 1997
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/j.1399-3054.1997.tb03434.x
Subject(s) - chemistry , photosynthesis , carbon fixation , total inorganic carbon , carbonic anhydrase , periplasmic space , electron transport chain , biophysics , membrane transport , nuclear chemistry , biochemistry , membrane , inorganic chemistry , carbon dioxide , enzyme , biology , organic chemistry , escherichia coli , gene
The ability of the morphologically complex cyanobacterium Chlorogloeopsis sp. ATCC 27193 to actively transport and accumulate inorganic carbon (C 1 = CO 2 + HCO 3 − + CO 3 2− ) for photosynthetic CO 2 fixation was investigated. Mass‐spectrometric assays revealed that Chlorogloeopsis cells grown under C 1 limitation rapidly took up CO 2 from the medium in a light‐dependent reaction which was independent of CO 2 fixation. Ethoxyzolamide, a carbonic anhydrase (CA) inhibitor, inhibited CO 2 transport. Since electrometric and mass‐spectrometric assays did not detect the presence of a periplasmic CA, it is suggested that CO 2 transport was mediated by a CA‐like activity which converted CO 2 to HCO 3 − during passage across the membrane. Radiochemical assays, using H 14 CO 3 as substrate, showed that C 3 ‐limited cells also had a high affinity (K 0.5 HCO 3 − = 37 μ M ), Na + ‐independent HCO 3 − uptake mechanism. HCO 3 − uptake was light dependent and occurred against its electrochemical potential indicating a carrier‐mediated, active transport process. The rate of Na + ‐independent HCO 3 − transport was sufficient to account for the steady state rate of CO 2 fixation. Although not absolutely required. Na + did specifically enhance the rate of HCO 3 − transport by up to 2‐fold, but had no effect on the apparent affinity of the transport system for HCO 3 − Combined CO 2 and HCO 3 − transport resulted in C 1 accumulation as high as 25 m M and in excess of 300 times the external concentration. The C 1 pool was the source of CO 2 for photo‐synthetic fixation and was generated, presumably, by the dehydration of HCO 3 − catalyzed by an intracellular CA. The collective evidence indicates that Chlorogloeopsis has a physiologically functional CO 2 ‐concentrating mechanism which is essential for photosynthesis.