Nitrous oxide reduction by two partial denitrifying bacteria requires denitrification intermediates that cannot be...

Area of Science:

• Microbial respiration and biogeochemical cycles
• Environmental microbiology and greenhouse gas mitigation

Background:

• Denitrification is a microbial process converting nitrate to dinitrogen gas through nitrogen oxide intermediates.
• Partial denitrifiers possess incomplete enzyme sets but can contribute to complete denitrification within communities.
• Nitrous oxide (N2O) is a potent greenhouse gas, making efficient denitrification crucial for climate change mitigation.

Purpose of the Study:

• To investigate if partial denitrifying bacteria sense and respond to denitrification intermediates they cannot metabolize.
• To elucidate the regulatory mechanisms of nitrous oxide (N2O) reduction in partial denitrifiers.
• To assess the implications of these regulatory interactions for microbial community function and greenhouse gas emissions.

Main Methods:

• Tested denitrifying capabilities of Rhodopseudomonas palustris CGA0092 (NO2- to N2) and Rhodobacter capsulatus SB1003 (N2O to N2).
• Assessed N2O reduction under varying conditions, including supplementation with denitrification intermediates.
• Utilized a beta-galactosidase reporter assay to study gene expression regulation by nitrate (NO3-).

Main Results:

• Both bacteria utilized N2O reduction for energy but required intermediate supplementation.
• Rhodopseudomonas palustris CGA0092 N2O reduction was activated by nitrate (NO3-), which stimulated N2O reductase gene expression.
• Rhodobacter capsulatus SB1003 N2O reduction was activated by nitrite (NO2-), suggesting a promiscuous enzyme activity.

Conclusions:

• Partial denitrifiers can sense and respond to denitrification intermediates not present in their own enzymatic repertoire.
• Nitrate (NO3-) and nitrite (NO2-) act as regulatory signals for N2O reduction in these bacteria, even without direct metabolism.
• Understanding these regulatory interactions is vital for optimizing denitrifying microbial communities to control greenhouse gas emissions.