Single cell analysis of bacteria using nano-Secondary Ion Mass Spectrometry (nanoSIMS) coupled to Laser Dissection Microscopy (LMD) and Atomic Force Microscopy (AFM)

The brackish Baltic Sea hosts annual events of massive cyanobacterial blooms, mainly consisting of three filamentous heterocystous types – Aphanizomenon sp., Nodularia sp., and Anabaena sp. The widespread occurence of these cyanobacteria is mostly triggered by high concentrations of phosphate, the main limiting factor for cyanobacterial growth, which is present due to anthropogenic riverine input into the Baltic Sea. Apart from their capability to perform photosynthesis in the vegetative cells, heterocystous cyanobacteria are also able to perform nitrogen fixation. It has been known for decades, that filamentous cyanobacteria, among others, are excellent habitats for heterotrophic bacteria growing in the extracellular layers. It is believed, that the heterotrophic bacteria lower oxygen levels through respiration, thereby creating favourable microzones of lower oxygen concentrations, in exchange for nutrients. These microzones might enhance nitrogen fixation and growth capacities of the cyanobacterium. The interactions of the different cyanobacterial types with the heterotrophic community in the Baltic are however likely to have a variety of mechanisms, which are, until now, poorly understood. My PhD projects aims at gaining insight into the nitrogen and carbon fixation capacities of the three important types of cyanobacteria in the Baltic Sea and study the mechanisms underlying the transfer of fixed carbon and nitrogen to associated microorganisms. Ultimately, the results of this project will help to better understand globally abundant cyanobacteria-bacteria interactions.