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Fundamental studies of microbial nitrogen transformations

Awarded: NOK 1.2 mill.

A core theme is the transcriptional regulation of the genes coding for nitrite reductase (NIR), nitric oxide reductase (NOR) and N2O reductase (NOS). Recently we have disovered stochastic transcription of NIR in the model bacterium, Paracoccus denitrificans, and strong expression of NOS in all cells. We have also discovered that the organism forms "persister cells" with an intact denitrifiction proteome, when transferred to oxic conditions. Through continued research on the model strain, we will try to understand the mechanisms involved. We will also investigate if similar diffeentiation occurs in other bacteria, when exposed to swithces between oxic and anoxic respiration. We have discovered that low pH effectively blocks/retard the synthesis of N2O reductase, with profound implications for N2O emission. Our aim is to find the reason(s) to this pH-effect, and will first test the hypothesis that the problem at low pH is the insertion of Cu into the protein. We have worked for several years with Rhizobia, and discovered that some strains are very strong sinks for N2O (hence reducing N2O emission to the atmopshere). We will investigate this further by quantifying enzymes, determine their turnver rates in vivo, and provide a plattform for understanding the regulation of their branched electron flow at th metabolic level. The project will ultimately provide crucial "in vivo" parameters that are needed for a systems biology apploach for understanding anaerobic respiration in denitrifying bacteria

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