Native metals, electron bifurcation, and CO₂ reduction in early biochemical evolution.

Area of Science:

• Biochemistry
• Astrobiology
• Geochemistry

Background:

• Molecular hydrogen (H2) and carbon dioxide (CO2) represent an ancient redox couple utilized by early life.
• Anaerobic autotrophs employing the H2/CO2 couple exhibit ancient biochemical traits linked to the universal common ancestor.
• Their physiology, including transition metal use and radical reaction mechanisms, connects early microbes to hydrothermal vent geochemistry.

Purpose of the Study:

• To investigate the paradox of how carbon dioxide (CO2) was reduced using molecular hydrogen (H2) before the evolution of proteins.
• To explore the potential role of native metals in early biochemical evolution and energy conservation.
• To understand the precursors of biological electron bifurcation mechanisms.

Main Methods:

• Analysis of anaerobic autotroph physiology, including acetogens and methanogens.
• Examination of the role of native iron (Fe0) in reducing CO2 to acetate and methanol in laboratory settings.
• Consideration of geochemical findings at hydrothermal vents, such as the presence of awaruite (Ni3Fe).

Main Results:

• Some acetogens and methanogens can utilize native iron (Fe0) as an electron donor instead of H2.
• Fe0 efficiently reduces CO2 to acetate and methanol under laboratory conditions.
• Native metals found at hydrothermal vents, like awaruite, suggest their potential role as precursors.

Conclusions:

• Native metals may have served as precursors to the flavin-based electron bifurcation mechanism crucial for CO2 fixation.
• This challenges the necessity of proteins for early H2/CO2 redox coupling.
• Native metals offer a plausible solution to the paradox of early CO2 reduction in the absence of complex biological machinery.