Secondary Metabolites
Competences
Bioactive metabolites
Bioactive metabolites: Producing organisms and plankton targets
Chemical interactions between species have been widely studied in terrestrial ecology but are less well known in marine ecosystems, especially among planktonic protists. In the marine plankton, temporal and spatial changes of biomass and species composition have traditionally been thought to be mainly regulated by resource availability and abiotic factors. However, there is increasing evidence that interspecific interactions in the plankton play a major role in succession, food web structure and bloom development. Many HAB species are regarded as rather poor exploitation competitors in terms of growth rate and/or resource uptake capabilities. There is some evidence for the hypothesis that a number of HAB species may gain dominance by the production of bioactive compounds, particularly secondary metabolites that affect growth or elicit other physiological responses in other organisms. Such allelochemicals may be targeted to exclude competitors from exploiting limited resources (interference competition), as well as to avoid/reduce predation.
By combining microscopy, protistan culture experiments and field surveys the following topics are worked on:
- Taxonomy, morphology, phylogeny, and behaviour of toxic protists
- Development and application of protist-interaction-based bioassays for identification of bioactive compounds
- Effects of chemical interactions on planktonic food webs
Bioactive compounds of toxic marine protist might be involved in competition and grazing interaction and/or might play a role in communication or may have other yet undetermined function.
Feeding interaction among plantonic dinoflagellates. The mixotrophic species Fragilidium subglobosum attacks and engulfs the larger spiny species Ceratium tripos.
Killing grazers and/or competitors by lytic compounds will favour bloom formation of harmful species.
Cellular targets
Visualisation of interactions and processes
To elicit any effect on living systems, natural and anthropogenic compounds target the smallest unit of the biota, the single cell. Small molecules may act as signaling molecules acting on chemoreceptors of cells or alter cellular signaling pathways by interaction with specific cellular compartments like ion channels, receptors or/and involved biochemical pathways. All these interactions may lead to a differential expression of genes and extensive changes of all organisational levels. We follow up these changes by physiological measurements of cellular signaling using optical (fluorescence microscopy) and electrophysiological (patch clamp and others) methods leaving the measured cell as undisturbed a possible. Therefore we focus mainly on live imaging techniques (multi photon laser scanning microscopy) using different approaches with fluorescence dyes and other fluorescent cellular compounds. The aim of this research is to define cellular targets of natural and anthropogenic small molecules.
Chemical analysis of secondary metabolites
Secondary metabolites are those chemical compounds of an organism that are not directly necessary for its survival, but often serve other functions such as feeding defense, intra- and/or interspecies communication, or quorum sensing. For this purpose, they are often produced only in small amounts. Some of these potent secondary metabolites are large organic molecules derived from polyketide biosynthesis. This group of molecules includes algal toxins (phycotoxins), which are classified into different groups but also show a large variability of structural variants within a group. However, the ecological function of phycotoxins is still largely unknown. There are also allelochemical compounds that have an effect on other marine organisms. The chemical structures of these compounds are in most cases still unknown.
The aim is to investigate the structural identity and variability of these compounds in order to draw conclusions about their function and thus about the adaptability of the producing organisms in a changing environment.
Tools
Team
Head of Laboratory:
Dr. Urban Tillmann (bioactive molecules / plankton ecology)
Dr. Ulf Bickemeyer (cellular targets)
Dr. Bernd Krock (chemical analysis of secondary metabolites)
Technicians:
Annegret Müller
Thomas Max
Ruben Lietzau
Visiting Scientists:
Dr. Marina Arregui (Universität Las Palmas)
PhDs:
Simon Tulatz
Tobias Müller