Main Research Interests
- Bioavailable nitrogen (N) is essential for every living organism and the main way new N is introduced into the biosphere is by dinitrogen (N2) fixation. For decades, the only important active diazotrophs have been thought to be filamentous cyanobacteria and cyanobacterial symbionts of diatoms. Only recently, it was shown that phototrophs can not explain completely the N2 fixation that occurs. N2 fixation has been found in non-cyanobacterial marine phyla, such as the Alpha- and Gammaproteobacteria. The study of heterotrophs is challenging the N2 fixation dogma, since hardly anything is known about single heterotrophic bacterial groups performing N2 fixation.
I am specifically focusing on a completely new bacterial phylum potentially involved in heterotrophic N2 fixation, which are the Spirochaetae. An additional and subsequent project is to investigate the physiology of different heterotrophic diazotrophs by using a novel approach called Correlative Imaging. First, the N2 fixation activity of single cells is identified with an immuno-assay visualizing active nitrogenase enzymes responsible for N2 fixation. Subsequently, the phylogeny of cells is identified by using catalyzed reported deposition–fluorescence in situ hybridization (CARD-FISH) on the same cell. The next approach uses the combination of nanoscale secondary ion mass spectrometry (nanoSIMS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy on a single positively identified diazotrophic cell. This approach will enable a deeper insight into activity and physiology of one single cell.