Our research focuses on mycoplankton interacting with phyto-, and bacterioplankton, and their functional role in the water column of brackish and marine systems. We cover topics such as fungal ecology and metabolism, interactions between microbial eukaryotes and prokaryotes, fungal parasites, nitrogen cycle, carbon fixation, functional genomics, and synthesis and breakdown of organic matter.

Publication list

Previous Projects

Fungal infections on phytoplankton – Cryptic perturbation of phytoplankton blooms

About half of the World’s primary production is attributed to phytoplankton although they account for less than 1% of the photosynthetically active biomass. Phytoplankton are therefore the base of aquatic food webs, and they fundamentally impact global biogeochemical cycles and the composition of our Earth’s atmosphere. Parasitic fungi are suggested to modulate phytoplankton growth and nutrient fluxes; however, quantitative estimates of this modulation are rare. In this project, we will elucidate the functional and quantitative role of fungal infections on phytoplankton for element cycling in the aquatic environment. The aim is to untangle microbial interactions during parasitic infections, in order to be able to integrate parasitic fungi into complex microbial networks.
PI: Isabell Klawonn, Ph.D. et al.

Phytoplankton colonies and marine snow – Heterogeneous Microenvironments

From a distant view, the ocean appears as a homogeneous fluid, where it seems intuitive to assume that organisms and nutrients are evenly distributed. However, in reality, there exist a microscale heterogeneity in the distribution of microbes and nutrients, e.g. around phytoplankton colonies and marine snow. Those particle represent microhabitats with physical, chemical and biological characteristics that are distinctly different from the ambient water. Using microsensor analyses, stable-isotope incubation and numerical modelling, we characterized the physical, chemical and biological micro-environment in Nodularia aggregates and Trichodesmium colonies. For instance, we showed that oxygen concentrations can vary from 0% to up to 200% air-saturation within these millimeter-sized particles, facilitating a diverse set of aerobic and anaerobic nitrogen cycling processes.
PI's: Prof. Helle Ploug and Prof. Hans-Peter Grossart, Postdoctoral researcher: Isabell Klawonn, Ph.D. et al.

Carbon and nitrogen fluxes during algae blooms – From single-cell to ecosystem-scale element cycling

Extensive blooms of dinitrogen-fixing cyanobacteria occur regularly during summer in the Baltic Sea. Nitrogen fixation during these blooms adds several hundred kilotons of new nitrogen into the Baltic Proper. Nitrogen-fixing cyanobacteria are therefore counteracting international effort to reduce nutrient loads into the Baltic Sea. In this project, as part of the interdisciplinary framework Baltic Ecosystem Adaptive Management, we resolved single-cell nitrogen and carbon fixation of Aphanizomenon, Dolichospermum and Nodularia, to quantify their taxa-specific share in nitrogen and carbon fixation. Moreover, we traced the fate of newly fixed nitrogen, after being released as ammonium, through the microbial food web in otherwise nitrogen-impoverished waters.
PI: Prof. Helle Ploug, Doctoral student: Isabell Klawonn et al.

Our methodologies include biogeochemical, microbiological and molecular tools. In particular, we use stable-isotope incubations, mass spectrometry (including GC-IRMS, EA-IRMS, nanoSIMS and IMS-1280), microscopy, roller-tank incubations, microsensor analyses, scanning electron microscopy, marker-gene sequencing, fluorescence in situ hybridization and nutrient analyses.