Plouviez Maxence, Wheeler David, Shilton Andy, Packer Michael A, McLenachan Patricia A, Sanz-Luque Emanuel, Ocaña-Calahorro Francisco, Fernández Emilio, Guieysse Benoit
School of Engineering and Advanced Technology, Massey University, Private Bag 11222, Palmerston North, New Zealand.
Institute of Fundamental Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand.
Plant J. 2017 Jul;91(1):45-56. doi: 10.1111/tpj.13544. Epub 2017 May 4.
Over the last decades, several studies have reported emissions of nitrous oxide (N O) from microalgal cultures and aquatic ecosystems characterized by a high level of algal activity (e.g. eutrophic lakes). As N O is a potent greenhouse gas and an ozone-depleting pollutant, these findings suggest that large-scale cultivation of microalgae (and possibly, natural eutrophic ecosystems) could have a significant environmental impact. Using the model unicellular microalga Chlamydomonas reinhardtii, this study was conducted to investigate the molecular basis of microalgal N O synthesis. We report that C. reinhardtii supplied with nitrite (NO ) under aerobic conditions can reduce NO into nitric oxide (NO) using either a mitochondrial cytochrome c oxidase (COX) or a dual enzymatic system of nitrate reductase (NR) and amidoxime-reducing component, and that NO is subsequently reduced into N O by the enzyme NO reductase (NOR). Based on experimental evidence and published literature, we hypothesize that when nitrate (NO ) is the main Nitrogen source and the intracellular concentration of NO is low (i.e. under physiological conditions), microalgal N O synthesis involves the reduction of NO to NO by NR followed by the reduction of NO to NO by the dual system involving NR. This microalgal N O pathway has broad implications for environmental science and algal biology because the pathway of NO assimilation is conserved among microalgae, and because its regulation may involve NO.
在过去几十年中，多项研究报告了微藻培养物以及以高藻类活性为特征的水生生态系统（如富营养化湖泊）中一氧化二氮（N₂O）的排放。由于N₂O是一种强效温室气体和消耗臭氧层的污染物，这些发现表明大规模培养微藻（以及可能的天然富营养化生态系统）可能会产生重大环境影响。本研究使用模式单细胞微藻莱茵衣藻来探究微藻N₂O合成的分子基础。我们报告称，在有氧条件下供应亚硝酸盐（NO₂⁻）的莱茵衣藻能够使用线粒体细胞色素c氧化酶（COX）或硝酸盐还原酶（NR）与偕胺肟还原成分的双酶系统将NO₂⁻还原为一氧化氮（NO），并且随后NO会被NO还原酶（NOR）还原为N₂O。基于实验证据和已发表的文献，我们推测当硝酸盐（NO₃⁻）是主要氮源且细胞内NO₂⁻浓度较低时（即在生理条件下），微藻N₂O合成涉及NR将NO₃⁻还原为NO₂⁻，随后由涉及NR的双系统将NO₂⁻还原为NO。这种微藻N₂O途径对环境科学和藻类生物学具有广泛影响，因为NO同化途径在微藻中是保守的，并且其调节可能涉及NO。
