• Background

  The last reports from IPCC (the Intergovernmental Panel on Climate Change) describe a steadily ongoing increase in the emissions of N2O, a potent greenhouse gas that is 300 times stronger than CO2  and also a main cause of the ongoing depletion of the stratospheric ozone layer. While implementation of climate policies will reduce the anthropogenic CO2 emissions substantially during the next decade(s), the anthropogenic N2O emissions are expected to continue to increase unless novel methods to reduce the N2O/N2 product ratio of our agroecosystems are invented. Denitrifying bacteria are responsible for the main part of the global N2O emissions from soils, primarily driven by excessive use of fertilizers. Denitrification is a microbial process where the organisms respire nitrate and other nitrogen oxides when oxygen becomes scarce. Many denitrifying bacteria both produce and consume N2O, and the amounts that are emitted depend on their regulatory biology. Although much is known about the details of this regulation, the current knowledge is mostly based on laboratory studies of organisms growing under optimal conditions. Surprisingly little is known about the regulation of denitrification in bacteria living under natural conditions, where they starve most of the time and are exposed to fluctuating oxygen concentrations that may harm the enzymes. Our recent research has shown that repeated fluctuation in oxygen availability could have profound implications, as illustrated by our recent discovery that in the model strain Paracoccus denitrificans, the return of oxygen induces formation of persister cells which preserve intact nitrite reductase, while the enzyme is degraded in the cells that engage in aerobic respiration and growth. The implications of these considerations are obvious: we need to study the regulation of denitrification in starving organisms that experience repeated transitions between oxic and anoxic conditions, both for a candid evaluation of proposed methods to reduce N2O emission, and to guide the search for others.

  In STARVOX we will dive deeper into how these stresses affect denitrifying organisms and their production of N2O. We will work on all scales spanning detailed enzyme studies, physiological analyses of bacterial isolates, and meta-omics based analyses of complex microbial communities. The results will add new knowledge to our understanding of the biogeochemical nitrogen cycle and will strengthen our ongoing development of novel methods for N2O mitigation where N2O reducing bacteria will be spread on farmland via biofertilization, via biodigestates or as rhizobial inoculants. The results will also feed into ongoing projects using denitrifying bacteria for single cell protein production, where fluctuating substrate- and oxygen levels are a challenge.

• Objectives

  Primary objective:

  The overarching goal of STARVOX is to improve our understanding of the transcriptional and metabolic regulation of denitrification under carbon/energy starvation and fluctuating oxygen conditions, needed for engineering of denitrifier communities to minimize the N2O emissions from soils, and for developing novel single-cell protein production based on denitrification.

  Secondary objectives:

  1. Unravel starvation effects on the regulation of denitrification at transcriptional, translational and metabolic level, using model strains which have contrasting denitrification phenotypes under well-fed conditions (WP1)
  2. Assess if the starvation effects observed in model strains apply to complex communities in natural ecosystems (WP2)
  3. Determine effects of oxidative stress and the fate of denitrification enzymes in model strains, when exposed to oxygen (WP3)
  4. Assess if the observed oxygen effects on denitrification enzymes in model strains apply to complex communities in natural ecosystems (WP4)
  5. Develop and optimize methods for turning off de novo synthesis of specific reductases and for quantitative determination of reductase abundancies (WP5)

• More about the project:

  Several researchers take part in STARVOX. These include several from the Microbial Ecology and Physiology Group (MEP); Protein Engineering group (PEP) and the Molecular Microbiology group (MolMic) at the Faculty of Chemistry, Biotechnology and Food Science, NMBU.

  The project is funded by the Research Council of Norway, program "Ground-breaking research". I addition, a faculty financed PhD student will be attached to the project (3 years, the position will be advertised in the end of January.

  Moreover, a post doc-level guest researcher, Cumhur Avsar, will contribute to STARVOX during one year from 1 April 2022. He is financed from the Scientific and Technological Research Council of Turkey (TUBITAK).

Researchers

From NMBU:

External researchers: