SGER: DMSP-Lyase Activity and CO2 Limitation in Marine Phytoplankton

碳酸氢盐（HCO3）在海洋表层水中溶解的无机碳库中占主导地位。虽然一些藻类可以直接利用HCO3，但海洋环境中驱动浮游植物光合作用的无机碳的主要来源是CO2。最近的研究表明，二氧化碳的可用性是大型海洋硅藻生长的潜在限制。在一些浮游植物物种中，二氧化碳直接在细胞膜上扩散，而其他浮游植物物种则利用HCO的转运体。碳酸酐酶（CA）将HCO3转化为CO2。在一些物种中发现细胞外CA活性，而其他物种则具有细胞内CA活性。硅藻等藻类是“二氧化碳使用者”，它们不直接吸收HC03离子，因此需要高水平的环境二氧化碳。相反，其他物种，如联生植物，可以在低二氧化碳条件下增殖。这种碳获取策略的差异提示了一种机制，即群落内浮游植物物种的组成可能受到碳限制的控制。一般来说，硅藻也是二甲磺酸丙酸（DMSP）的不良生产者，并且含有很少或没有DMSP裂解酶。另一方面，触觉植物是DMSP的重要生产者，具有较高的DMSP裂解酶活性。海藻中DMSP和裂解酶的细胞功能一直存在争议。通过DMSP分解DMSP？裂解酶释放二甲基硫化物（DMS）、丙烯酸和质子。迪图里奥博士假设通过裂解酶释放的质子？介导反应允许DMSP？裂解酶在低CO2条件下通过迫使碳酸盐/碳酸氢盐体系向CO2平衡而有效利用HCO3。这使得这些物种减轻了碳限制，并在非？DMSP吗?在低二氧化碳环境中生产物种。这个实验室吗?本项目将检验联生植物DMSP产量与碳限制正相关的假设。

Bicarbonate (HCO3) dominates the dissolved inorganic carbon pool in the surface waters of the ocean. While some algal species can utilize HCO3 directly, the major source of inorganic carbon driving phytoplankton photosynthesis in the marine environment is CO2. Recent work indicates that the availability Of CO2 is a potential limit on the growth of large marine diatoms. Diffusion of CO2 across the cell membrane occurs directly in some phytoplankton species while others utilize a transporter for HCO?3 uptake, with the HCO3 converted to CO2 by carbonic anhydrase (CA). Extracellular CA activity is found in some species while others have intracellular CA activity. Algal species such as diatoms are"CO2-users" and do not take up HC03 ions directly, requiring high ambient levels of CO2. Conversely, other species such as haptophytes can proliferate under conditions of low CO2. This difference in carbon acquisition strategy suggests a mechanism whereby the composition of phytoplankton species within a community may be controlled by carbon limitation. In general, diatoms are also poor producers of dimethylsulfoniopropionate (DMSP) and contain little or no DMSP?lyase. On the other hand, haptophytes are important producers of DMSP and have high DMSP lyase activity. The cellular function of DMSP and the lyase enzyme in algae is controversial. Breakdown of DMSP via the DMSP?lyase enzyme liberates dimethylsulfide (DMS), acrylic acid and protons. Dr. DiTullio hypothesizes that the release of protons via the lyase?mediated reaction allows those species with the DMSP?lyase enzyme to effectively utilize HCO3 under conditions of low CO2 by forcing the equilibria of the carbonate/bicarbonate system toward CO2. This allows these species to alleviate carbon limitation and dominate over non?DMSP?producing species in low CO2 environments. This laboratory?based project will test the hypothesis that DMSP production in haptophytes is positively correlated to carbon limitation.