Origin and Evolution of Nitrogen Fixation in Prokaryotes
Hong-Wei Pi1,2, Jinn-Jy Lin2, Chi-An Chen2,3
1Ph.D. Program in Microbial Genomics, National Chung Hsing University and Academia Sinica, Taiwan.
Molecular Biology and Evolution
|August 22, 2022
Summary
Nitrogen fixation, essential for life, likely originated in bacteria, not archaea. This study
Area of Science:
- Evolutionary biology
- Microbiology
- Genomics
Background:
- Nitrogen is vital for all life, but only certain bacteria and archaea can fix it.
- The prevailing theory suggests nitrogen fixation evolved first in archaea, then transferred to bacteria.
- However, nitrogen-fixing (Nif) bacteria are more numerous and diverse than Nif archaea.
Purpose of the Study:
- To investigate the evolutionary origin of nitrogen fixation.
- To compare the prevailing archaea-first hypothesis with the proposed bacteria-first hypothesis.
- To analyze genomic and protein sequence data from over 30,000 prokaryotic genomes.
Main Methods:
- Identified six key nitrogen fixation genes (Nif genes) across sequenced prokaryotic genomes.
- Reconstructed phylogenetic trees using individual and combined Nif proteins.
- Analyzed molybdenum transporter genes (ModABC and WtpABC) and their protein sequences (ModA and WtpA).
Main Results:
- Phylogenetic analyses consistently showed the earliest Nif protein lineages as bacterial.
- Archaeal Nif sequences were nested within bacterial clades, indicating bacterial origin.
- Most Nif archaea utilize the bacterial molybdenum transporter system (ModABC), not the archaeal one (WtpABC).
- Phylogeny of molybdenum transporter proteins also supported an earlier bacterial origin.
Conclusions:
- The study provides strong evidence supporting the bacteria-first hypothesis for the evolution of nitrogen fixation.
- Nitrogen fixation likely originated in bacteria and was subsequently transferred to archaea.
- Genomic and phylogenetic data challenge the long-held archaea-first theory.
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