The following study was conducted by Scientists from aAix Marseille Univ, CEA, CNRS, Institut de Biosciences et Biotechnologies Aix-Marseille, CEA Cadarache, Saint Paul-Lez-Durance, France. Study is published in Proceedings of the National Academy of Sciences Journal as detailed below.
Proceedings of the National Academy of Sciences (2020); 117(5): 2704-2709
Algal Photosynthesis Converts Nitric Oxide into Nitrous Oxide
Significance
Nitrous oxide (N2O), the third most important greenhouse gas in the atmosphere, is produced in great quantities by microalgae, but molecular mechanisms remain elusive. Here we show that the green microalga Chlamydomonas reinhardtii produces N2O in the light by a reduction of NO driven by photosynthesis and catalyzed by flavodiiron proteins, the dark N2O production being catalyzed by a cytochrome p450. Both mechanisms of N2O production are present in chlorophytes, but absent from diatoms. Our study provides an unprecedented mechanistic understanding of N2O production by microalgae, allowing a better assessment of N2O-producing hot spots in aquatic environments.
Abstract
Nitrous oxide (N2O), a potent greenhouse gas in the atmosphere, is produced mostly from aquatic ecosystems, to which algae substantially contribute. However, mechanisms of N2O production by photosynthetic organisms are poorly described. Here we show that the green microalga Chlamydomonas reinhardtii reduces NO into N2O using the photosynthetic electron transport. Through the study of C. reinhardtii mutants deficient in flavodiiron proteins (FLVs) or in a cytochrome p450 (CYP55), we show that FLVs contribute to NO reduction in the light, while CYP55 operates in the dark. Both pathways are active when NO is produced in vivo during the reduction of nitrites and participate in NO homeostasis. Furthermore, NO reduction by both pathways is restricted to chlorophytes, organisms particularly abundant in ocean N2O-producing hot spots. Our results provide a mechanistic understanding of N2O production in eukaryotic phototrophs and represent an important step toward a comprehensive assessment of greenhouse gas emission by aquatic ecosystems.
Source:
Proceedings of the National Academy of Sciences
URL: https://www.pnas.org/content/early/2020/01/14/1915276117
Citation:
Burlacot, A., P. Richaud, et al. (2020). “Algal photosynthesis converts nitric oxide into nitrous oxide.” Proceedings of the National Academy of Sciences 117(5): 2704-2709.
