Characterization of a CO2-Concentrating Mechanism with Low Sodium Dependency in the Centric Diatom Chaetoceros gracilis
Characterization of a CO2-Concentrating Mechanism with Low Sodium Dependency in the Centric Diatom Chaetoceros gracilis
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DOI：
10.1007/s10126-021-10037-4
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发表时间：
2021-06-09
影响因子：
3
通讯作者：
Fukuzawa, Hideya
中科院分区：
文献类型：
--
作者：
Tsuji, Yoshinori;Kusi-Appiah, George;Fukuzawa, Hideya
微藻通过协调无机碳（Ci）转运蛋白和碳酸酐酶（CAs），诱导CO2浓缩机制（CCM）来克服水环境中的CO2限制胁迫。已经提出了两种机制，以促进CI从水介质中的摄取：Na+依赖的HCO 3-吸收溶质载体（SLC）家族转运蛋白和加速脱水的HCO 3-CO2的外部CA在模型硅藻。然而，对具有重要生态和工业价值的硅藻，包括水产养殖中常见的食物来源--纤细角毛藻的研究仍然有限。本文对C. gracilis使用抑制剂和生长依赖Na+和CO2。在CO2限制性胁迫条件下，加入膜不可渗透的SLC抑制剂4，4 '-二异硫氰基-2，2'-二苯乙烯二磺酸（DIDS）或从培养基中瞬时去除Na+并不损害对Ci的光合亲和力，但加入膜不可渗透的CA抑制剂乙酰唑胺使Ci亲和力降低到对照培养物的三分之一。在含0.23 mM Na+C的培养基中。在含5%CO_2的空气中，纤细草光合自养生长，而在含0.04%CO_2的空气中则不能。这些结果表明C. gracilis在其CCM中利用外部CA来提高对Ci而不是质膜SLC家族转运蛋白的光合亲和力。此外，可能的是，低水平的Na+可以支持CCM在质膜上的Ci-吸收以外的过程中，特别是在CO2限制条件下。我们的研究结果为硅藻中CCM的多样性提供了见解，并为优化工业应用的培养条件提供了基本信息。
Microalgae induce a CO2-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.