Segregation of nitrogen fixation and oxygenic photosynthesis in the marine cyanobacterium Trichodesmium
Segregation of nitrogen fixation and oxygenic photosynthesis in the marine cyanobacterium Trichodesmium
复制标题
DOI：
10.1126/science.1064082
复制
发表时间：
2001-11-16
期刊：
影响因子：
56.9
通讯作者：
Falkowski, P
中科院分区：
文献类型：
--
作者：
Berman-Frank, I;Lundgren, P;Falkowski, P
在现代海洋中，大量的固氮作用归因于毛藻属的丝状非异囊蓝藻。在这些生物体中，固氮作用仅限于光周期，并与含氧光合作用同时发生。固氮酶是负责生物 N-2 固定的酶，在体外会受到氧气不可逆的抑制。如何保护固氮酶免受光合作用产生的 O-2 的损害曾经是一个谜。使用快速重复率荧光测定和荧光动力学显微镜，我们表明光周期内 N-2 固定和光合作用存在时间和空间分离。线性光合电子传递通过减少光系统 I (PSI) 中光合演化的 O-2 来保护固氮酶。我们假设，在含氧光合作用的早期进化阶段，固氮酶充当厌氧异养代谢的电子受体，并且PSI受到选择的青睐，因为它为蓝藻中的N-2固定提供了微厌氧环境。
In the modern ocean, a significant amount of nitrogen fixation is attributed to filamentous, nonheterocystous cyanobacteria of the genus Trichodesmium. In these organisms, nitrogen fixation is confined to the photoperiod and occurs simultaneously with oxygenic photosynthesis. Nitrogenase, the enzyme responsible for biological N-2 fixation, is irreversibly inhibited by oxygen in vitro. How nitrogenase is protected from damage by photosynthetically produced O-2 was once an enigma. Using fast repetition rate fluorometry and fluorescence kinetic microscopy, we show that there is both temporal and spatial segregation of N-2 fixation and photosynthesis within the photoperiod. Linear photosynthetic electron transport protects nitrogenase by reducing photosynthetically evolved O-2 in photosystem I (PSI). We postulate that in the early evolutionary phase of oxygenic photosynthesis, nitrogenase served as an electron acceptor for anaerobic heterotrophic metabolism and that PSI was favored by selection because it provided a micro-anaerobic environment for N-2 fixation in cyanobacteria.