[B-BG01] Earth and Planetary Science Frontiers for Life and Global Environment

[BBG01-06] Reconstruction of evolutionary history from the nitrogenase-oxidoreductase family revealed timings of the origins of nitrogen fixation and photosynthesis

*Arisa Nishihara¹, Yusuke Tsukatani², Chihiro Azai³, Moriya Ohkuma¹, Masaru Konishi Nobu⁴ (1.RIKEN BioResource Research Center, 2.Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3.College of Life Sciences, Ritsumeikan University, 4.The National Institute of Advanced Industrial Science and Technology (AIST))

Keywords:comparative genomics, nitrogen fixation, photosynthesis, molecular clock

Early life evolved by developing new nutrient acquisition mechanisms to adapt to diverse environments. The geological record shows signs that some key metabolic innovations in Earth’s history, nitrogen fixation and photosynthesis, may have appeared at least 3.2 billion years ago, yet currently no conclusive molecular evidence is available. In this study, we reconstructed the intertwined evolutionary history of prokaryotes and a large protein family including core proteins of nitrogen fixation, photosynthesis, and methanogenesis – the nitrogenase-oxidoreductase family – through phylogenetic analyses, comparative genomics, and molecular clock analyses. In doing so, we improved constraints on the timing at which nitrogen fixation and photosynthesis originated.

For constructing the nitrogenase-oxidoreductase family tree, 12,934 amino acid sequences from 19,972 archaeal and bacterial genomes were used. Based on clustering of the proteins and colocalization information, the family could be divided into 26 different protein groups, including 15 uncharacterized proteins. Most of the groups were divided into two supergroups – one related to the nitrogenase molybdenum-iron protein alpha chain (NifD) and the other the beta chain (NifK).Molecular clock analysis of a phylogenetic tree of NifK-related genes estimated that the timing of the origin of photosynthesis and nitrogen fixation are 3.7-3.1 Ga and 3.0-2.3 Ga, respectively, which coincides with geological signatures interpreted as signs of early nitrogen fixation (3.2-2.75 Ga) and photosynthesis (3.22 to 3.77 Ga, earliest banded iron formation). Our study illuminates critical progressions and events in the intertwined evolutionary relationship between phylogenetic relationship and Earth.