The DIVERSITY Group within the Dep. of Microbiology (Prof. Dr. F. Widdel) offers several themes for research projects and bachelor or master theses, as well Praxissemester project for students from applied universities (Fachhochschulen). Prof. Jens Harder has supervised in the last 10 years 29 praxis term students and Erasmus exchanges as well as 56 bachelor and master theses.
Biochemistry and physiology: Characterization of the physiology of anaerobic microorganisms (cultivation of anaerobes, metabolite characterization and quantification by GC and HPLC techniques)
Physiology and taxonomy: Isolation and characterization of aerobic microorganisms (cultivation of aerobes, genetic characterization by 16S rRNA gene sequencing), currently we focus on flavobacteria and polysaccharide degradation
Prof. Dr. Jens Harder
Available Master Thesis Projects in Biogeochemistry
Currently open Masters Degree level projects in the Biogeochemistry Group are listed below at:
The fate of fixed-nitrogen and -carbon released by a unicellular diazotrophic cyanobacterium
Two-thirds of the world ocean euphotic zone, encountered in the (sub)-tropical areas, is known as nitrogen limited habitat (Falkowski et al., 1998). In such environment, biological N2 fixation (or diazotrophy) is an important process by which some exclusively prokaryotic organisms (i.e. diazotrophs) can access to the largest nitrogen reservoir on Earth (i.e N2 gas) and turn it into an usable nitrogen form (NH4+) to support primary production. By doing this conversion, diazotrophs acting as “natural fertilizers” and contribute to sustain life and carbon export (Mahaffey et al., 2005). Early studies considered both Trichodesmium and the heterocystous Richelia as the major marine N2 fixers. However, unicellular diazotrophic cyanobacteria (UCYN) were found to fix N2 gas at high rates, equaling or exceeding the N2 fixation rates found in Trichodesmium (Montoya et al., 2004).
Among the UCYN organisms, unicellular diazotrophs of the genus Crocosphaera sp. are depicted as an important provider of new nitrogen (Montoya et al., 2004). Recently, it had been shown that C. watsonii could excrete up to 80% of its fix nitrogen (Dron et al., 2012a; 2013), mainly as dissolved organic nitrogen (DON). Recent investigations uncover that C. watsonii is also able to produce as well an important amount of dissolved organic carbohydrates (Sohm et al., 2011; Dron et al., 2012b). Such excretion of dissolved organic carbon and nitrogen is depicted to stimulate the growth of heterotrophic bacteria and phytoplankton respectively, especially in nutrient poor water.
We thus stress the need to examine the biochemical interactions between unicellular diazotrophic and other microorganisms (i.e. heterotorphic bacteria and phytoplankton). The student will focus on the trophic transfer of fixed-carbon and –nitrogen from C. watsonii to heterotrophic bacteria and phytoplankton. This project is innovative because since to date there are no published data on the fate of fixed-nitrogen (ammonium and/or DON) and fixed-carbon released by C. watsonii.