A nitrite-oxidising bacterium constitutively consumes atmospheric hydrogen

Area of Science:

• Microbiology
• Environmental Science
• Biogeochemistry

Background:

• Chemolithoautotrophic nitrite-oxidising bacteria (NOB) of the genus Nitrospira are crucial for nitrification.
• Nitrospira are believed to tolerate substrate limitation due to high nitrite affinity and alternative energy use.

Purpose of the Study:

• To investigate the ability of Nitrospira moscoviensis to oxidize hydrogen (H₂).
• To understand the role of H₂ oxidation in NOB growth and survival under varying nitrite conditions.
• To explore the implications for the nitrogen and hydrogen cycles.

Main Methods:

• Enzyme kinetics measurements to determine the affinity for H₂.
• Proteomic analysis to assess protein abundance under different conditions.
• Thermodynamic modeling to evaluate energy yield from H₂ and nitrite oxidation.

Main Results:

• Nitrospira moscoviensis utilizes a high-affinity hydrogenase to oxidize H₂ at sub-atmospheric levels (Km(app) = 32 nM).
• H₂ oxidation supports growth and survival under both nitrite-replete and nitrite-deplete conditions.
• Proteomics revealed metabolic adjustments for energy conservation under nitrite limitation.
• Thermodynamic modeling indicated H₂ oxidation provides a higher power yield at low substrate concentrations.

Conclusions:

• Atmospheric H₂ oxidation enhances NOB growth and survival amidst fluctuating nitrite availability.
• This phenomenon is now recognized in the Nitrospirota phylum, extending its known occurrence.
• The study uncovers significant links between the global hydrogen and nitrogen cycles, suggesting H₂ is a primary energy source for some NOB.