Anaerobic ammonia oxidation with nitrogen dioxide by Nitrosomonas eutropha

Area of Science:

• Microbial Ecology
• Biogeochemical Cycles
• Environmental Microbiology

Background:

• Nitrosomonas eutropha is an obligate lithoautotroph.
• Simultaneous nitrification and denitrification are crucial microbial processes.

Purpose of the Study:

• To investigate the ability of Nitrosomonas eutropha to perform nitrification and denitrification concurrently.
• To determine the role of nitrogen dioxide (NO2) in these processes under anoxic conditions.

Main Methods:

• Culturing Nitrosomonas eutropha under anoxic conditions with supplemented gaseous nitrogen dioxide (NO2).
• Monitoring ammonia oxidation, nitrite formation, denitrification to dinitrogen (N2), and intermediates like nitric oxide (NO) and nitrous oxide (N2O).
• Measuring bacterial growth (cell protein and number) and cellular energy content (ATP and NADH).

Main Results:

• Nitrosomonas eutropha achieved simultaneous nitrification and denitrification when NO2 was supplied.
• 40-60% of produced nitrite was denitrified to N2, with N2O as an intermediate.
• Bacterial growth and cellular ATP/NADH content increased significantly in the presence of NO2, indicating energy generation.
• Nitric oxide (NO) was found to inhibit anaerobic ammonia oxidation.

Conclusions:

• Nitrosomonas eutropha can effectively couple nitrification and denitrification under specific anoxic conditions.
• The process supports bacterial growth and energy metabolism, highlighting its ecological significance.
• Nitrogen dioxide availability is a key factor enabling these dual functions in this bacterium.