Criteria and methodology for identifying respiratory denitrifiers

Area of Science:

• Microbiology
• Environmental Science

Background:

• Respiratory denitrification is crucial for nitrogen cycling but often difficult to confirm in bacteria.
• Established methods may not always adequately verify the two key criteria for denitrification.

Purpose of the Study:

• To present a simple, reliable method for evaluating respiratory denitrification in microorganisms.
• To establish definitive criteria for confirming denitrification, including N(inf2) or N(inf2)O production coupled to growth.

Main Methods:

• Culturing microorganisms in sealed tubes with varying nitrate/nitrite concentrations under helium.
• Quantifying N(inf2) and N(inf2)O via gas chromatography and measuring final protein concentration.
• Assessing nitrogen gas production rates and correlating them with protein yield.

Main Results:

• Net protein production showed a linear relationship with nitrate concentration for all tested denitrifiers.
• Nitrogen recovery as N(inf2) plus N(inf2)O exceeded 80% for all denitrifiers.
• A high rate of N gas production (>10 (mu)mol/min/g protein) was identified as a definitive characteristic.

Conclusions:

• The proposed method effectively confirms respiratory denitrification by meeting established criteria.
• The criteria successfully distinguished true denitrifiers from other nitrate-reducing or N(inf2)O-producing bacteria.
• This approach is valuable for identifying weak denitrifiers where the process might otherwise be overlooked.