1. Characterization of a CO 2 -Concentrating Mechanism with Low Sodium Dependency in the Centric Diatom Chaetoceros gracilis.
- Author
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Tsuji Y, Kusi-Appiah G, Kozai N, Fukuda Y, Yamano T, and Fukuzawa H
- Subjects
- 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid pharmacology, Acetazolamide pharmacology, Carbon metabolism, Carbonic Anhydrase Inhibitors pharmacology, Seawater chemistry, Sodium, Carbon Dioxide metabolism, Diatoms metabolism, Photosynthesis
- Abstract
Microalgae induce a CO
2 -concentrating mechanism (CCM) to overcome CO2 -limiting stress in aquatic environments by coordinating inorganic carbon (Ci) transporters and carbonic anhydrases (CAs). Two mechanisms have been suggested to facilitate Ci uptake from aqueous media: Na+ -dependent HCO3 - uptake by solute carrier (SLC) family transporters and accelerated dehydration of HCO3 - to CO2 by external CA in model diatoms. However, studies on ecologically and industrially important diatoms including Chaetoceros gracilis, a common food source in aquacultures, are still limited. Here, we characterized the CCM of C. gracilis using inhibitors and growth dependency on Na+ and CO2 . Addition of a membrane-impermeable SLC inhibitor, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), or the transient removal of Na+ from the culture medium did not impair photosynthetic affinity for Ci in CO2 -limiting stress conditions, but addition of a membrane-impermeable CA inhibitor, acetazolamide, decreased Ci affinity to one-third of control cultures. In culture medium containing 0.23 mM Na+ C. gracilis grew photoautotrophically by aeration with air containing 5% CO2 , but not with the air containing 0.04% CO2 . These results suggested that C. gracilis utilizes external CAs in its CCM to elevate photosynthetic affinity for Ci rather than plasma-membrane SLC family transporters. In addition, it is possible that low level of Na+ may support the CCM in processes other than Ci-uptake at the plasma membrane specifically in CO2 -limiting conditions. Our findings provide insights into the diversity of CCMs among diatoms as well as basic information to optimize culture conditions for industrial applications., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)- Published
- 2021
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