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Response of Ammonia Oxidizing Bacteria to Ammonia Starvation

Ammonia-oxidizing bacteria fulfill an important biological role in the nitrogen cycle as they carry out the first reaction in the oxidative pathway of the cycle. These bacteria obtain energy for growth from the oxidation of ammonia and acquire the majority of their carbon through the fixation of CO2 via the Calvin Cycle. Notably, these bacteria are found in wastewater treatment plants where they aid removal of nitrogenous waste and in agricultural soils where they are responsible for the depletion of ammonia based fertilizers.

nitrogen cycle figure

The Nitrogen Cycle (image by Thomas Donn). Microorganisms are responsible for the majority of nitrogen cycling in the environment. Nitrifying microorganisms are responsible for the oxidation of ammonia to nitrite (ammonia-oxidizers) and the oxidation of nitrite to nitrate (nitrite-oxidizers). Although most nitrifiers are aerobic, the recently discovered process of anaerobic ammonia oxidation (ANAMMOX) has shown that ammonia-oxidation takes place in anoxic environments. The reductive pathway is entirely anaearobic and is characterized by the use of oxidized nitrogen compounds as alternative electron acceptors in the process of denitrification. Nitrogen fixation completes the cycle by returning nitrogen gas to bioavailable ammonia.

Ammonia-oxidizing bacteria are also known to be unusually resistant to starvation conditions. In contrast to typical heterotrophic bacteria, ammonia-oxidizing bacteria maintain a high level of viability during starvation without cellular differentiation or degradation of endogenous macromolecules such as RNA or protein. It is thought that a low maintenance energy requirement during starvation is partly responsible for this resistance. In addition, Nitrosomonas europaea can immediately respond to the addition of ammonia after nearly one year of starvation, likely due to the high stability of the enzymes in the ammonia oxidation pathway. High survival rates during starvation and the ability to rapidly respond and utilize ammonia when it is available both contribute to this unique starvation response strategy.

Research in the Stahl Laboratory utilizes genetics, biochemistry, and physiology to study the cellular processes of Nitrosomonas europaea that are involved in starvation resistance and the ability of this organism to immediately respond to ammonia following both short and long term periods of starvation. In particular, several of our research interests include:

  • Regulation of ammonia monooxygenase expression during growth, starvation, and recovery from starvation.

  • Biochemical role of an alternative ammonia monoxygenase subunit (amoC3) that is expressed specifically during recovery from starvation.

  • Global response of Nitrosomonas europaea to nutrient limitation and other stressors.


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