Effects of Nitrate on Hydrogenogenic Carbon Monoxide Oxidation in Parageobacillus thermoglucosidasius

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Parageobacillus thermoglucosidasius utilizes nickel-containing CO dehydrogenase (Ni-CODH) and energy-converting hydrogenase (ECH) for hydrogenogenic carbon monoxide (CO) oxidation.
• The effect of nitrate on CO oxidizers is contradictory, with reported promoting or inhibitory impacts on growth and CO oxidation.

Purpose of the Study:

• To investigate the impact of nitrate on hydrogenogenic CO oxidation and growth in P. thermoglucosidasius NBRC 107763^T.
• To elucidate the relationship between nitrate availability and CO oxidation mechanisms in this thermophilic bacterium.

Main Methods:

• Utilized wild-type and genetically modified strains (codh- and/or ech-disrupted) of P. thermoglucosidasius.
• Quantified CO oxidation, hydrogen production, and cell growth (OD₆₀₀) under varying nitrate concentrations.
• Performed cell lysate assays to pinpoint the effect of nitrate on CO-oxidizing function.

Main Results:

• 50 mM nitrate significantly suppressed hydrogenogenic CO oxidation but promoted hydrogen-oxidizing nitrate reduction and rapid cell growth (2.3-fold higher OD₆₀₀).
• 10 μM nitrate in cell lysates inhibited CO oxidation below detection limits while maintaining hydrogen production, indicating a direct effect on the CO-oxidizing system.
• CO oxidation is primarily coupled to proton reduction and is deactivated during nitrate respiration.

Conclusions:

• Hydrogenogenic CO oxidation in P. thermoglucosidasius functions as an auxiliary energy-acquiring pathway, active primarily in the absence of alternative electron acceptors like nitrate.
• Nitrate respiration is a preferred metabolic strategy over CO oxidation in P. thermoglucosidasius.
• Findings clarify the role of CO in energy metabolism and suggest its supplemental use in this organism.