Bacteria fixing N2 in the sea – a combination of microbiology, molecular biology and marine biology

Målgruppe:Biology, Bioinformatics, Biochemistry
Niveau:Masters, Bachelor

N2 (dinitrogen) fixation by prokaryotic microorganisms represents a major external source of nitrogen to the ocean. In some areas, N2 fixation can cover up to half of the nitrogen demand of primary production in the sunlit surface layer of the pelagial. Most studies on N2 fixation have revolved around N2-fixing (diazotroph) cyanobacteria, but more recent work has shown that many heterotrophic bacteria must also be important. However, many unknowns remain about these diazotroph bacteria. An especially important shortcoming of studying N2 fixation in the ocean is that traditional methods to measure rates of N2 incorporation might underestimate the true rates, and might particularly miss the contributions from these small, heterotrophic bacteria.

The advertised project will center around improving our knowledge about the ecological relevance of heterotroph diazotrophs in the ocean, using a combination of molecular and biogeochemical method approaches. Genes encoding Nitrogenase, the enzyme that is essential for N2 fixation, will be targeted by PCR amplification and cloning, to reveal which bacteria in the water carry this gene and thus may fix N2. Based on this, the expression of these genes in identified specific bacteria will be quantified using Real-Time PCR. The 15N2 tracer method for direct measurements of N2 fixation rates in field samples will be thoroughly tested by not only analyzing tracer enrichment in the recovered cell material, but by also screening this material for the presence of specific diazotroph key players, and by analyzing whether any of these key players are lost to the filtrate using the traditional methods. The findings may have important consequences for the overall marine N budget, and would likely be a great opportunity to produce a major scientific article.

There is some flexibility about how exactly this project would be organized. It would become part of a larger research project, and the diverse approach using microbial, molecular and biogeochemical methods would provide the successful candidate with a great set of skills that could subsequently be used in many contexts, in- and outside of marine microbial ecology.

You will be part of a team in a molecular biology laboratory at the Marine Biological section located in Helsingør. The project will be led by Prof. Lasse Riemann.


Phone 35321959, Email:

Keywords:Marine biology, microbiology, molecular biology, bacteria, ecology
Vejleder(e): Lasse Riemann