Unique H₂-utilizing lithotrophy in serpentinite-hosted systems

Area of Science:

• Microbiology
• Geochemistry
• Astrobiology

Background:

• Serpentinization of ultramafic rocks generates molecular hydrogen (H2), supporting microbial life.
• Extreme conditions in these systems include hyperalkalinity and low CO2 levels, challenging conventional microbial metabolisms.

Purpose of the Study:

• To investigate microbial metabolism in serpentinization-active systems.
• To identify novel taxa and metabolic pathways adapted to H2-rich, CO2-poor environments.

Main Methods:

• Metagenomics to identify microbial taxa and genes.
• Thermodynamic analysis to assess metabolic feasibility.
• Environmental surveying of serpentinite-hosted microbiomes.

Main Results:

• Conventional H2/CO2-dependent homoacetogenesis is thermodynamically unfavorable due to extremely low CO2 concentrations.
• A novel phylum, "Ca. Lithacetigenota," was discovered, exclusively inhabiting serpentinite systems.
• These microbes utilize formate and glycine, not CO2, for H2-based lithotrophy via unique pathways, including glycine reductase.

Conclusions:

• "Ca. Lithacetigenota" employs ancient, non-CO2-dependent H2-utilizing metabolisms, such as catabolic glycine reduction.
• This adaptation allows life to thrive in hyperalkaline, CO2-limited serpentinite environments.
• These findings offer insights into primordial lithotrophy on early Earth and extremophile survival strategies.