Inorganic-carbon uptake by a small-celled strain ofStichococcus bacillaris
✍ Scribed by J. Muñoz; M. J. Merrett
- Publisher
- Springer-Verlag
- Year
- 1988
- Tongue
- English
- Weight
- 502 KB
- Volume
- 175
- Category
- Article
- ISSN
- 0032-0935
No coin nor oath required. For personal study only.
✦ Synopsis
Air-grown cells of a marine, small-celled (2 lam diameter) strain of Stichococcus bacillaris contained appreciable carbonic-anhydrase activity but this was repressed when cells were grown on air enriched with 5 % (v/v) CO2. Assay of carbonicanhydrase activity using intact cells and cell extracts showed all activity was intracellular in this Stichococcus strain. Measurement of inorganiccarbon-dependent photosynthetic O2 evolution at pH 5.0, where CO2 is the predominant form of inorganic carbon, showed that the concentration of inorganic carbon required for half-maximal rate of photosynthetic O2 evolution [Ko.5(C02) ] was 4.0 txM for both air-and CO2-grown cells. At pH 8.3 the K0.s (CO2) was 0.3 mM for air-grown and 0.6 mM for CO2-grown cells. Sodium ions did not enhance bicarbonate utilization. Measurement of the internal inorganic-carbon pool (HCO~ + CO2) by the silicone-oil-layer centrifugal filtering technique showed that air-and CO2-grown cells were able to concentrate inorganic carbon up to 20-fold in relation to the external medium at pH 5.0 but not at pH 8.3. In this alga the high affinity for CO2 and inorganic-carbon accumulation in CO2-and air-grown cells results from active CO2 transport that is not dependent on carbonicanhydrase activity.