As photosynthetic organisms, algae (unicellular and multicellular) almost make the same contribution to global carbon fixation as the land plants. Our research is focused on algal metabolism and the interactions of microalgae with other microorganisms.
We exploit available genome sequences from algae to find hints for yet unknown metabolites, and to identify biosynthetic routes to known compounds. In the laboratory, we are combining genetic strategies with physiological and chemical-analytical methods to elucidate the benefit of specific compounds and proteins for the algal cell.
We hope that our research will provide ecological insights into algal lifestyle and improve our understanding of how algae interact with their environment and other organisms. In addition, the investigation of algal metabolism may lead to the discovery of biotechnologically or pharmaceutically useful compounds and processes.
We regularly offer projects for theses on the research areas listed above. To enquire about projects, please contact Prof. Dr. Severin Sasso.
Our research activities
Microalgae occur ubiquitously in water and soil. As photosynthetic primary producers, they are situated at the basis of the food web. Therefore, the interactions of microalgae with other organisms will influence biogeochemial fluxes and the structure of communities. Well-known examples of such mixed communities include lichens or corals.
On the molecular level, little is known about the interactions between microalgae and other microbes. We are using well-defined model systems to dissect such interactions in the laboratory. For example, we aim at identifying the identity of exchanged nutrients, signals, genes and proteins involved in these interactions. In one project, which is part of the Collaborative Research Centre Chemical Mediators in Complex Biosystems (www.chembiosys.de), we are studying the molecular interplay between the unicellular model alga Chlamydomonas reinhardtii and various bacteria from soil (collaboration partner: Prof. Maria Mittag, University of Jena).
Further reading
- Aiyar, P.; Schaeme, D.; García-Altares, M.; Flores, D. C.; Dathe, H.; Hertweck, C.; Sasso, S.; Mittag, M.
Antagonistic bacteria disrupt calcium homeostasis and immobilize algal cells.
Nat Commun. 2017. 8:1–13. - Hom EFY, Aiyar P, Schaeme D, Mittag M, Sasso S.
A chemical perspective on microalgal–microbial interactions.
Trends in Plant Science. 2015. 20:689–693. - Kazamia, E.; Czesnick, H.; Nguyen, T. T. V.; Croft, M. T.; Sherwood, E.; Sasso, S.; Hodson, S. J.; Warren, M. J.; Smith, A. G.
Mutualistic interactions between vitamin B12-dependent algae and heterotrophic bacteria exhibit regulation.
Environmental Microbiology. 2012. 14:1466–1476.
Secondary metabolites (specialised metabolites) are typically restricted to certain species, and often involved in the interaction of the producing species with its environment. Our aim is to characterise new secondary metabolites in algae and identify their functions. For example, some dinoflagellate microalgae produce toxic polyketides during the formation of harmful algal blooms, and these polyketides contribute to the damage caused by such blooms (intoxication of animals and humans). Surprisingly, genome sequencing projects have unveiled a number of polyketide biosynthetic genes also in non-toxic algae. Some of these predicted genes have giant sizes, but their functions have remained enigmatic. We intend to identify the corresponding algal polyketides and their physiological and ecological function.
Further reading
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Heimerl, N.; Hommel, E.; Westermann, M.; Meichsner, D.; Lohr, M.; Hertweck, C.; Grossman, A. R.; Mittag, M.; Sasso, S.
A giant type I polyketide synthase participates in zygospore maturation in Chlamydomonas reinhardtii.
The Plant Journal. 2018. 95:268–281. -
Shelest, E.; Heimerl, N.; Fichtner, M.; Sasso, S.
Multimodular type I polyketide synthases in algae evolve by module duplications and displacement of AT domains in trans.
BMC Genomics. 2015. 16:1015.
Algae and higher plants use the conversion of special pigments to protect the photosynthetic apparatus against damage induced by high light illumination. The pigments, which are generated in the so-called xanthophyll cycles, induce a structural change of the light-harvesting complexes of the photosystems. This structural rearrangement leads to the transformation of excessive light energy into harmless heat. The enzymatic conversion of the xanthophylls takes place in a biomembrane, the thylakoid membrane. The activity of the xanthophyll cycle enzymes depends on the presence of special membrane lipids and the lipid structures formed by these lipids. Our research in the field of xanthophyll cycles deals with the interaction of membrane lipids, the xanthophyll cycle enzymes and the antenna complexes, which usually bind the xanthophylls. In further experiments, we want to analyze the molecular mechanism which leads to the transformation of light energy into heat in the antenna complexes of the photosystems. Investigations of the xanthophyll cycles are performed in higher plants and diatoms. Additional experiments include the investigation of the protein composition, the structure and function of the xanthophyll-binding light-harvesting complexes in diatoms.
Further reading
- Bojko, M.; Olchawa‐Pajor, M.; Goss, R.; Schaller‐Laudel, S.; Strzałka, K.; Latowski, D.
Diadinoxanthin de-epoxidation as important factor in the short-term stabilization of diatom photosynthetic membranes exposed to different temperatures.
Plant, Cell & Environment. 2019. 42:1270–1286. - Goss, R.; Greifenhagen, A.; Bergner, J.; Volke, D.; Hoffmann, R.; Wilhelm, C.; Schaller-Laudel, S.
Direct isolation of a functional violaxanthin cycle domain from thylakoid membranes of higher plants.
Planta. 2017. 245:793–806. - Schaller-Laudel, S.; Volke, D.; Redlich, M.; Kansy, M.; Hoffmann, R.; Wilhelm, C.; Goss, R.
The diadinoxanthin diatoxanthin cycle induces structural rearrangements of the isolated FCP antenna complexes of the pennate diatom Phaeodactylum tricornutum.
Plant Physiology and Biochemistry. 2015. 96:364–376.
Various biotic (e.g. pathogenes) and abiotic stress factors (e.g. UV, humic substances) act on the photosynthetic performance of algae and can have detrimental effects on development and hence on overall growth rate. Measurements of variable chlorophyll fluorescence, thermoluminescence, and gas-exchange provide detailed information on the photosynthetic apparatus, its regulation and specific target sites under stress conditions. Additionally, formation of reactive oxygen species (ROS) can result in oxidative stress leading to degradation of cell components, e.g. lipids (lipid peroxidation). Using specific biochemical markers or high temperature thermoluminescence, degradation products can be detected and the level of damage in algal cells evaluated. However, characterizing the stress-physiological state of algae can also provide valuable information on further research topics of our scientific team, e.g. on interactions of microalgae with other microorganisms or on secondary metabolites (e.g. antioxidants, ovothiol in C. reinhardtii).
Further reading
- Gilbert, M.; Bährs, H.; Steinberg, C.E.W.; Wilhelm, C.
The artificial humic substance HS1500 does not inhibit photosynthesis of the green alga Desmodesmus armatus in vivo but interacts with the photosynthetic apparatus of isolated spinach thylakoids in vitro.
Photosynth Research. 2018. 137:403–420. - Lepetit, B.; Volke, D.; Gilbert, M.; Wilhelm, C.; Goss, R.
Evidence for the existence of one antenna-associated, lipid-dissolved and two protein-bound pools of diadinoxanthin cycle pigments in diatoms.
Plant Physiology. 2010. 154:1905–1920. - Gilbert, M.; Wagner, H.; Weingart, I.; Skotnica, J.; Nieber, K.; Tauer, G.; Bergmann, F.; Fischer, H.; Wilhelm, C.
A new type of thermoluminometer: A highly sensitive tool in applied photosynthesis research and plant stress physiology.
Journal of Plant Physiology. 2004. 161:641–651.
Microalgae use absorbed light energy and assimilated carbon for biomass production. The comparison of different algal classes revealed differences in the light use efficiency (quantum efficiency) but also in the efficiency of usage of assimilated carbon for biomass production. The differences are caused by e.g. light protecting mechanisms, alternative electron pathways, and metabolic pathways that influence cellular carbon allocation and finally, the composition and energy content of algal biomass. The energy and carbon allocation can be investigated by a combination of different methods, e.g. Chlorophyll fluorescence, gas exchange measurements, and Infrared (FTIR) spectroscopy. Finally, this combination of methods provides a general view on the carbon and energy flux within algal cells in dependence on environmental parameters (e.g. light conditions, nutrient supply, temperature, pH value) but also as a consequence of the mutual interaction of phytoplankton, and interaction with other microorganisms. The understanding of cellular energy and carbon allocation patterns is important for the interpretation of different growth strategies of phytoplankton, and for the modeling of biomass production in bioreactors as well as of aquatic primary production in the field.
Further reading
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Grund, M.; Jakob, T.; Toepel, J.; Schmid, A.; Wilhelm, C.; Bühler, B. Heterologous lactate synthesis in Synechocystis sp. strain PCC 6803 causes a growth condition-dependent carbon sink effect. Applied and Environmental Microbiology. 2022. 88:e00063-22.
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Grund, M.; Jakob, T.; Wilhelm, C.; Bühler, B.; Schmid, A. Electron balancing under different sink conditions reveals positive effects on photon efficiency and metabolic activity of Synechocystis sp. PCC 6803. Biotechnology for Biofuels. 2019. 12:43.
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Wagner, H.; Jakob, T.; Fanesi, A.; Wilhelm, C. Towards an understanding of the molecular regulation of carbon allocation in diatoms: the interaction of energy and carbon allocation. Philosophical Transactions of the Royal Society B: Biological Sciences. 2017. 372:20160410.
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Dunker, S.; Jakob, T.; Wilhelm, C. Contrasting effects of the cyanobacterium Microcystis aeruginosa on the growth and physiology of two green algae, Oocystis marsonii and Scenedesmus obliquus, revealed by flow cytometry. Freshwater Biology. 2013. 58:1573–1587.
Gibberellins are plant hormones that coordinate their precisely timed development. They are important for regulation of e.g. stem elongation, germination, dormancy, flowering, leaf senescence and fruit development. More recently it was also revealed that gibberellins can alter the induction of plant defense against herbivores and pathogens. For those reasons their biosynthesis and mode of action are well studied in plants and the plant pathogenic fungus Gibberella fujikuroi. Both pathways evolved independently from each other. We could recently show that bacteria are also able to produce gibberellins and that their biosynthesis pathway evolved independently from plants and fungi. Surprisingly gibberellins are produced by pathogenic and symbiotic bacteria. We are interested to characterize individual enzymatic reactions of the bacterial pathway and to investigate the interplay between bacterial pathogens and their host plants in more detail.
Further reading
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Nagel, R.; Peters, RJ.
Diverging Mechanisms: Cytochrome-P450-catalyzed demethylation and γ-lactone formation in bacterial gibberellin biosynthesis.
Angewandte Chemie. 2018. 130:6190–6193. -
Nagel, R.; Peters, RJ.
Investigating the phylogenetic range of gibberellin biosynthesis in bacteria.
Molecular Plant-Microbe Interactions. 2017. 30:343–349. -
Nagel, R.; Turrini, PCG.; Nett, RS.; Leach, JE.; Verdier, V.; Sluys, M-AV.; Peters, RJ.
An operon for production of bioactive gibberellin A4 phytohormone with wide distribution in the bacterial rice leaf streak pathogen Xanthomonas oryzae pv. oryzicola.
New Phytologist. 2017. 214:1260–1266.
As sessile organisms, plants are exposed to various environmental stresses. Therefore, they require different molecular and physiological mechanisms to survive under undesirable conditions such as flooding, drought, and nutrient deficiency. This provides a very exciting field of research that is directly connected to the current and future challenges in the environment, agriculture, and food supply.
Green algae, on the other hand, are close relatives of land plants. As some green microalgae grow quickly and are amenable to genetic modification, we are using them as easy systems to explore their response to abiotic stress. Comparing the molecular and cellular mechanisms will permit a broad perspective on stress tolerance in land plants and green algae.
Our research program focuses on the major threats to plants in the context of climate change and its impacts on agriculture and food production:
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investigating the genes and molecular players involved in stress response and tolerance, e.g. hypoxia, drought, and nitrogen deficiency
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exploring the role of nitric oxide (NO) as a signal molecule under abiotic stress conditions in land plants and green algae as well as its role in mycorrhiza symbiosis
To achieve these aims, we apply a combination of plant physiology and molecular biology techniques. Arabidopsis thaliana and Chlamydomonas reinhardtii serve as model species and tomato (Solanum lycopersicum) is investigated as an important crop.
Eventually, the outcome of this research will shed more light on the responses to abiotic stress and unravel how land plants and green algae interact with their environment. Investigating the stress response has the potential for improving the stress resistance of crops and minimizing yield loss due to global warming.
„New Green Chemistry” is a novel approach to produce organic carbon for industrial use or for energy production by means of photosynthesis without the generation of biomass. The photosynthetically fixed carbon is excreted instead of being used for biomass production. The advantage of this approach is that the conversion efficiency from photon to the product is at least one order of magnitude higher and the demand of limiting plant nutrients (like phosphorus, nitrogen or potassium) is negligible.
This research topic is offered by the group of SenProf. Christian Wilhelm.