H+ fluxes in phytoplankton - a mechanistic and modelling study of their physiological roles and impact upon community responses to ocean acidification

浮游植物中的 H 通量 - 其生理作用及其对海洋酸化群落反应影响的机制和模型研究

• 批准号: NE/J021296/1
• 负责人: Glen Wheeler
• 金额: $ 7.8万
• 依托单位: Plymouth Marine Laboratory
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ021296%2F1
• 关键词: H+; fluxes; phytoplankton; mechanistic; modelling

The oceans remove about half of the carbon dioxide (CO2) that we release into the atmosphere and produce about half of the oxygen that we breathe. The photosynthetic marine phytoplankton play a major role in these processes, contributing to global carbon, nitrogen and sulphur cycling. Phytoplankton are not simply single-celled plants. They represent an extremely diverse collection of algae with many novel traits and complex evolutionary histories which are still poorly understood. The increase in atmospheric carbon dioxide due to the burning of fossil fuels has major climatic implications. A result of the oceans absorbing much of this CO2 is the acidification of surface ocean waters - a drop from pH 8.2 to pH 7.7 is predicted by the end of the century. As ocean pH has remained stable for many millions of years this may have profound effects on many marine organisms that have not previously experienced this level of pH or rate of change during their recent evolutionary history. Ocean acidification will also change the levels of carbonate and nutrient ions, all of which may have significant impacts on the physiology of marine phytoplankton. While some of these impacts are being intensively studied, the direct effect of decreased pH itself on phytoplankton physiology has been largely overlooked. Marine phytoplankton, like all organisms, must tightly regulate their cellular pH by in order to maintain favourable conditions for cellular processes. We have been studying mechanisms of pH regulation in coccolithophores, an important group of phytoplankton that play a major role in the global carbon cycle through their production of calcium carbonate scales (coccoliths) which sink to the deep ocean following cell death. We have discovered that coccolithophores use protein pores (channels) in their outer cell membrane to regulate pH inside the cell. These channels allow H+ to exit from the cell whenever acidity in the cell increases, thus acting to keep pH inside the cell constant. This is particularly important for coccolithophores as the production of coccoliths in the cell results in a constant production of H+ which need to be removed or the acidity inside of the cell would increase to dangerous levels. This novel mechanism is extremely sensitive to changes in external pH and may no longer function effectively at near future ocean pH levels. We have also found this form of H+ channel in diatoms, the most numerous and productive group of phytoplankton. Remarkably, we have found that coccolithophore cells acclimated in the laboratory to growth at lower pH no longer appear to use a H+ channel. While this suggests coccolithophores may be able to cope with lower pH, we do not know the wider or long-term physiological implications of this mechanistic switch. This is clearly something we urgently need to understand. This project will examine in detail the mechanisms of pH homeostasis in coccolithophores and diatoms. Our modelling studies predict that mechanisms of cellular pH regulation are likely to differ in large and small phytoplankton species as these will experience greatly different fluctuations in pH at the cell surface due to physical effects of cell size on diffusion at the cell surface. We propose that different mechanisms of pH homeostasis employed by phytoplankton species may play a major role in the response of these organisms to ocean acidification. In order to gauge how these novel aspects of phytoplankton physiology will impact upon marine ecosystems on a broader scale, we will use modelling approaches to examine how cellular H+ fluxes in phytoplankton cells respond to changes in their environment. These mathematical models will enable us to predict the ranges of pH experienced by different phytoplankton species both currently and in the future and will allow us to evaluate their impact on the diversity of natural phytoplankton populations that will be studied in related programmes.

海洋带走了我们释放到大气中的大约一半的二氧化碳，产生了我们呼吸的大约一半的氧气。光合作用的海洋浮游植物在这些过程中起主要作用，促进全球碳、氮和硫的循环。浮游植物不是简单的单细胞植物。它们代表了极其多样化的藻类集合，具有许多新奇的特征和复杂的进化历史，这些特征和历史仍然知之甚少。由于燃烧化石燃料而增加的大气二氧化碳对气候有重大影响。海洋吸收大量二氧化碳的结果是海洋表层海水酸化——预计到本世纪末，pH值将从8.2降至7.7。由于海洋pH值在数百万年里保持稳定，这可能对许多海洋生物产生深远的影响，这些生物在其最近的进化史中以前没有经历过这种pH值水平或变化速度。海洋酸化还会改变碳酸盐和营养离子的水平，所有这些都可能对海洋浮游植物的生理产生重大影响。虽然其中一些影响正在被深入研究，但pH值降低本身对浮游植物生理的直接影响在很大程度上被忽视了。海洋浮游植物和所有生物一样，必须严格调节其细胞pH值，以维持有利的细胞过程条件。我们一直在研究球石藻的pH调节机制，球石藻是一种重要的浮游植物，通过生产碳酸钙鳞片（球石藻）在细胞死亡后沉入深海，在全球碳循环中发挥重要作用。我们发现球石藻利用其外细胞膜上的蛋白质孔（通道）来调节细胞内的pH值。当细胞酸度增加时，这些通道允许H+从细胞中流出，从而保持细胞内的pH值恒定。这对球石藻尤其重要，因为细胞中球石藻的产生会导致H+的不断产生，H+需要被去除，否则细胞内的酸度会增加到危险的水平。这种新机制对外部pH值的变化极为敏感，可能在不久的将来海洋pH值水平下不再有效地起作用。我们还在硅藻中发现了这种形式的H+通道，硅藻是浮游植物中数量最多、产量最高的一类。值得注意的是，我们发现在实验室中适应较低pH生长的球石细胞似乎不再使用H+通道。虽然这表明球石藻可能能够应对较低的pH值，但我们不知道这种机制转换的更广泛或长期的生理影响。这显然是我们迫切需要了解的。本项目将详细研究球石藻和硅藻pH稳态的机制。我们的模型研究预测，由于细胞大小对细胞表面扩散的物理影响，大型和小型浮游植物物种的细胞pH调节机制可能会有所不同，因为这些浮游植物在细胞表面的pH波动会有很大不同。我们认为浮游植物不同的pH稳态机制可能在这些生物对海洋酸化的响应中起重要作用。为了衡量浮游植物生理学的这些新方面将如何在更广泛的范围内影响海洋生态系统，我们将使用建模方法来检查浮游植物细胞中的细胞H+通量如何响应其环境的变化。这些数学模型将使我们能够预测当前和未来不同浮游植物物种所经历的pH值范围，并使我们能够评估它们对自然浮游植物种群多样性的影响，这些影响将在相关计划中进行研究。

项目成果

The role of coccolithophore calcification in bioengineering their environment.

• DOI: 10.1098/rspb.2016.1099
• 发表时间: 2016-06-29
• 期刊: Proceedings. Biological sciences
• 作者: Flynn KJ;Clark DR;Wheeler G
• 通讯作者: Wheeler G

Ocean acidification with (de)eutrophication will alter future phytoplankton growth and succession.

• DOI: 10.1098/rspb.2014.2604
• 发表时间: 2015-04-07
• 期刊: Proceedings. Biological sciences
• 作者: Flynn KJ;Clark DR;Mitra A;Fabian H;Hansen PJ;Glibert PM;Wheeler GL;Stoecker DK;Blackford JC;Brownlee C
• 通讯作者: Brownlee C

Dynamic changes in carbonate chemistry in the microenvironment around single marine phytoplankton cells.

• DOI: 10.1038/s41467-017-02426-y
• 发表时间: 2018-01-08
• 期刊: Nature communications
• 影响因子: 16.6
• 作者: Chrachri A;Hopkinson BM;Flynn K;Brownlee C;Wheeler GL
• 通讯作者: Wheeler GL

The Marine Microbial Eukaryote Transcriptome Sequencing Project (MMETSP): illuminating the functional diversity of eukaryotic life in the oceans through transcriptome sequencing.

• DOI: 10.1371/journal.pbio.1001889
• 发表时间: 2014-06
• 期刊: PLoS biology
• 影响因子: 9.8
• 作者: Keeling PJ;Burki F;Wilcox HM;Allam B;Allen EE;Amaral-Zettler LA;Armbrust EV;Archibald JM;Bharti AK;Bell CJ;Beszteri B;Bidle KD;Cameron CT;Campbell L;Caron DA;Cattolico RA;Collier JL;Coyne K;Davy SK;Deschamps P;Dyhrman ST;Edvardsen B;Gates RD;Gobler CJ;Greenwood SJ;Guida SM;Jacobi JL;Jakobsen KS;James ER;Jenkins B;John U;Johnson MD;Juhl AR;Kamp A;Katz LA;Kiene R;Kudryavtsev A;Leander BS;Lin S;Lovejoy C;Lynn D;Marchetti A;McManus G;Nedelcu AM;Menden-Deuer S;Miceli C;Mock T;Montresor M;Moran MA;Murray S;Nadathur G;Nagai S;Ngam PB;Palenik B;Pawlowski J;Petroni G;Piganeau G;Posewitz MC;Rengefors K;Romano G;Rumpho ME;Rynearson T;Schilling KB;Schroeder DC;Simpson AG;Slamovits CH;Smith DR;Smith GJ;Smith SR;Sosik HM;Stief P;Theriot E;Twary SN;Umale PE;Vaulot D;Wawrik B;Wheeler GL;Wilson WH;Xu Y;Zingone A;Worden AZ
• 通讯作者: Worden AZ