Magnesium Isotope Fractionation during Synthesis of Chlorophyll a and Bacteriochlorophyll a of Benthic Phototrophs in Hypersaline Environments
Magnesium Isotope Fractionation during Synthesis of Chlorophyll a and Bacteriochlorophyll a of Benthic Phototrophs in Hypersaline Environments
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DOI：
10.1021/acsearthspacechem.9b00013
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发表时间：
2019-06-01
影响因子：
3.4
通讯作者：
Ohkouchi, Naohiko
中科院分区：
文献类型：
--
作者：
Isaji, Yuta;Yoshimura, Toshihiro;Ohkouchi, Naohiko
镁是细胞中主要的二价阳离子，对维持细胞功能至关重要。氯色素的镁同位素组成（δ Mg-26）可能提供有关涉及Mg的细胞物理和生化反应的详细信息;然而，现有数据很少，其控制因素仍未得到解决。在这里，我们报告三角洲镁-26的叶绿素a和细菌叶绿素a来自蓝藻和紫硫细菌栖息在浅的高盐环境下形成的底栖微生物垫和石膏结壳。卤水中Mg同位素从源Mg ~（2+）向正、负方向分馏（δ Mg-26，从每千份-1.05至-0.78份）叶绿素a含量为-1.77 ~-0.39ppm;细菌叶绿素a，从-2.13到-0.12份每千），表明多个过程参与叶绿素生物合成过程中的镁分馏。细菌叶绿素a的δ Mg-26和δ N-15之间的关系表明δ Mg-26值与光养生物的生长速率之间存在相关性。我们建议，在镁插入步骤的动力学同位素分馏的程度的变化，在响应细胞的氯色素的量，导致在自然环境中观察到的氯色素的三角洲镁-26的大的变化。
Magnesium is a major divalent cation in the cell and is vital for maintaining cellular function. The magnesium isotopic composition (delta Mg-26) of chloropigments potentially provides detailed information on cellular physical and biochemical reactions that involve Mg; however, existing data are scarce, and its controlling factors remain unresolved. Here, we report delta Mg-26 of chlorophyll a and bacteriochlorophyll a derived from cyanobacteria and purple sulfur bacteria that inhabit benthic microbial mats and gypsum crusts formed under shallow hypersaline environments. There was substantial Mg isotope fractionation in both positive and negative directions from source Mg2+ in the brine (delta Mg-26, from -1.05 to -0.78 parts per thousand) to chloropigments (chlorophyll a, from -1.77 to -0.39 parts per thousand; bacteriochlorophyll a, from -2.13 to -0.12 parts per thousand), suggesting that multiple processes are involved in the fractionation of Mg during chlorophyll biosynthesis. The relationship between delta Mg-26 and delta N-15 of bacteriochlorophyll a indicates a correlation between delta Mg-26 values and the growth rate of phototrophs. We suggest that the extent of kinetic isotopic fractionation during the Mg-insertion step changes in response to the amounts of cellular chloropigments, resulting in the large variability in delta Mg-26 of chloropigments observed in natural environments.