Nitric oxide preferentially inhibits nitrite oxidizing communities with high affinity for nitrite

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Biogeochemical cycling

Background:

• Partial nitritation/anammox processes require out-selection of nitrite oxidizing bacteria (NOB).
• Nitric oxide (NO) production under cyclic oxic-anoxic conditions is a potential strategy for NOB out-selection.
• Nitrobacter species are known to be inhibited by NO, but the effect on Nitrospira is unstudied.

Purpose of the Study:

• To quantify the effect of nitric oxide (NO) on the nitrite oxidation activity of NOB, focusing on Nitrospira.
• To understand the relationship between NO inhibition and Nitrospira's nitrite affinity.
• To assess NO's impact on NOB in different sludge compositions relevant to wastewater treatment.

Main Methods:

• Quantification of NO effect on nitritation activity in sludge with varying Nitrobacter/Nitrospira ratios.
• Use of an oxic bubbling column to dose NO and measure inhibition.
• Experimental setup with artificial alginate-based biofilm for direct NO exposure.

Main Results:

• Nitrobacter-dominated sludge showed 24% inhibition with NO dosage.
• Nitrospira-dominated sludge inhibition varied from 0% to 80%, strongly correlated with nitrite half saturation constant (K(s)).
• High-affinity Nitrospira (low K(s)) were significantly inhibited by NO, confirming K-strategist sensitivity.

Conclusions:

• Nitric oxide strongly inhibits Nitrospira, a prevalent NOB genus in wastewater treatment.
• The sensitivity of Nitrospira to NO is linked to their high affinity for nitrite.
• NO can be a tool to out-select NOB, particularly Nitrospira, in partial nitritation/anammox processes.