Nitrobacter winogradskyi transcriptomic response to low and high ammonium concentrations

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Nitrobacter winogradskyi is a nitrite-oxidizing bacterium.
• Nitrite oxidation is often coupled with ammonium oxidation in natural environments.
• Ammonium (NH4(+)) can serve as both an energy and nitrogen source.

Purpose of the Study:

• To investigate the effect of ammonium (NH4(+)) on the growth and gene expression of Nitrobacter winogradskyi.
• To understand how N. winogradskyi adapts its physiology in the presence of varying NH4(+) concentrations.
• To explore the implications for coupled nitrification processes.

Main Methods:

• Culturing Nitrobacter winogradskyi in media with different ammonium (NH4(+)) concentrations.
• Analyzing bacterial growth rates.
• Performing whole-genome gene expression analysis (transcriptomics).

Main Results:

• Ammonium (NH4(+)) concentrations above 35 mM delayed growth, while concentrations below 25 mM were well-tolerated.
• N. winogradskyi adjusted the expression of 24% of its genes in response to NH4(+).
• Upregulation of genes involved in nitrogen and carbon assimilation, particularly glutamate synthase (GOGAT), was observed at higher NH4(+) levels. Genes for assimilatory nitrite metabolism, glycogen degradation, and motility were downregulated.

Conclusions:

• Nitrobacter winogradskyi exhibits significant physiological adaptation to ammonium (NH4(+)) availability.
• The bacterium modifies gene expression related to nutrient assimilation and cellular processes in response to NH4(+).
• These findings suggest that NH4(+) influences N. winogradskyi physiology, impacting its role in coupled nitrification.