Geobiological feedbacks, oxygen, and the evolution of nitrogenase

Area of Science:

• Biochemistry
• Evolutionary Biology
• Microbiology

Background:

• Nitrogenase, a vital enzyme, facilitates biological nitrogen fixation, enabling increased global productivity and the evolution of complex life.
• Nitrogenase enzymes contain intricate iron-sulfur cofactors, with three main types distinguished by their active site metal clusters (Molybdenum, Vanadium, or Iron-only).
• Alternative nitrogenases (Vanadium-dependent or Iron-only) exhibit lower N2 reduction activity and are expressed when Molybdenum is absent.

Purpose of the Study:

• To review advances in understanding biological nitrogen fixation.
• To explore the emergence, evolution, and distribution of nitrogenase.
• To emphasize key events in nitrogenase's diversification from anoxic to oxic environments.

Main Methods:

• Phylogenetic analysis to trace the evolutionary history of nitrogen fixation.
• Isotopic evidence to date the earliest nitrogenase activity.
• Review of existing literature on nitrogenase function and adaptation.

Main Results:

• Biological nitrogen fixation originated in anaerobic, thermophilic ancestors and spread through lateral gene transfer.
• Nitrogenase activity existed as early as 3.2 billion years ago, before oxygenic photosynthesis.
• Diazotrophic organisms evolved oxygen protection mechanisms and metabolic strategies for nitrogen fixation in aerobic environments.

Conclusions:

• Nitrogenase evolution is intrinsically linked to Earth's changing atmospheric conditions.
• The diversification of nitrogenase reflects adaptations to both anoxic and oxic environments.
• Understanding nitrogenase evolution provides insights into early life and global biogeochemical cycles.