Microbiological evidence for Fe(III) reduction on early Earth

Area of Science:

• Microbiology
• Geochemistry
• Evolutionary Biology

Background:

• Sulphur reduction is traditionally considered an early microbial respiration method.
• Geochemical data suggests iron(III) reduction may have preceded sulphur reduction in early microbial metabolism.
• Microorganisms related to the last common ancestor are often anaerobic, sulphur-reducing hyperthermophiles.

Purpose of the Study:

• To investigate the potential of early microorganisms to utilize iron(III) as an external electron acceptor.
• To determine if Archaea and Bacteria closely related to the last common ancestor can perform Fe(III) respiration.
• To explore the metabolic capabilities of hyperthermophiles, specifically Thermotoga maritima, regarding Fe(III) reduction.

Main Methods:

• Cultivation of microorganisms, including Thermotoga maritima, with Fe(III) as the sole external electron acceptor.
• Monitoring microbial growth and energy conservation through Fe(III) to Fe(II) reduction.
• Comparative analysis of microbial metabolisms, contrasting Fe(III) reduction with sulphur reduction.

Main Results:

• Archaea and Bacteria closely related to the last common ancestor can conserve energy and grow via Fe(III) respiration.
• Thermotoga maritima, previously thought to be solely fermentative, demonstrated growth as a respiratory organism with Fe(III).
• Microbiological evidence supports Fe(III) reduction as a significant early metabolic process.

Conclusions:

• Fe(III) reduction likely played a crucial role in early Earth's microbial metabolism.
• Modern hot biospheres may harbor microorganisms contributing to Fe(III) reduction.
• Hyperthermophiles can be cultivated without sulphur, facilitating biochemical studies by avoiding toxic byproducts.