Research

Research projects:

"Chemical ecology of cross-kingdom interactions"

The focus of our research group is to elucidate the mutualistic interactions between prokaryotes and eukaryotes ("cross-kingdom cross-talk"). Our previous work has shown that challenges of chemical ecology - at the interface between biology and chemistry - can only be resolved successfully by an interdisciplinary research approach. The consistent combination of classical bioassays and chemical analytical methods reveals novel insights into the complex networks of infochemicals and signal molecules along with their ecophysiological significance. Our research approach focuses on the fundamental understanding of the functioning of infochemicals in biocoenoses that can be mimicked in laboratory studies after which field experiments are conducted to prove their ecological significance.

To reach this goal, we have developed the marine green seaweed Ulva (Chlorophyta) into a model organisms.

Major research initiatives have been established:

I. Studies of the symbiotic interactions between bacteria and marine macroalgae

- To decipher the chemosphere of the marine green algae Ulva sp. and its associated bacteria.

- To understand the cross kingdom talk of bacteria and Ulva sp. based on infochemicals.

II. Regulation of gametogenesis and gametes release in Ulva

- To identify sporulation inhibitors controlling the differentiation of blade cells into gametangia

III. Studies of metal-recruitment by algae and bacteria via metallophores

- To identify metallophores for the metal uptake by these bacteria.

- To measure the bioavailability of trace metals essential for the nitrogenase.

Ulva was selected as the Alga of the Year 2015.

I. Symbiotic interactions of the marine macroalgae Ulva and its associated bacteria

Tripartite Community of Ulva
Image: Wichard (2015) Frontiers in Plant Science

Tripartite community and representative morphotypes. Tripartite community of U. mutabilis with proposed essential interactions for standardized experimental set-ups. A combination of Roseobacter sp. (MS2) and Cytophaga sp. (MS6) excreting morphogenetic substances recover growth and morphogenesis of the wildtype (shown in the top) and the mutant slender of U. mutabilis: Roseobacter sp. promotes cell division (A: scale bars = 1 mm) and Cytophaga sp. promotes rhizoid and cell wall formation (B: scale bars = 1 mm). Strictly axenic cultures develop into a callus like morphotype consisting of undifferentiated cells without normal cell walls. Image: © Wichard T (2015) Exploring bacteria-induced growth and morphogenesis in the green macroalga order Ulvales (Chlorophyta). Front. Plant Sci. 6:86. doi: 10.3389/fpls.2015.00086External link. This project is funded by the Colaborative Research Center "Chemical Mediators In Complex Biosystems" ChemBioSys SFB 1127 - Project A01External link.

II. Regulation of gametogenesis and gametes release in Ulva

Induction and regulation of gametogenesis and zoosporogenesis in Ulva mutabilis and Ulva linza. Phenotypic changes of blade cells during gametogenesis and gamete release. (A) Blade cells 24 h after induction resemble uninduced blade cells: cells are square and often in transverse rows. (B) 48 h after induction, blade cells differentiate into gametangia containing finally 16 progametes, which mature during the following night into fully developed gametes ready for swarming. (C,D) Gametes are discharged in the morning of the third day. (E) Discharged sporangia and (F) zoospores within a sporangium are shown. Gametophytes (A-D) and sporophytes (E,F) were grown under standard conditions (Scale bars: A,B,D = 25 μm; C = 140 μm, E = 16 μm, F = 4 μm). Image: © Vesty EF, Kessler RW, Wichard T and Coates JC (2015) Regulation of gametogenesis and zoosporogenesis in Ulva linza (Chlorophyta): comparison with Ulva mutabilis and potential for laboratory culture. Front. Plant Sci. 6:15. doi: 10.3389/fpls.2015.00015External link.

III. Determination and quantification of metallophores

Metallophore mapping
Image: Deicke et al. (2014) Analyst

Metal isotope coded profiling (MICP) introduces a universal discovery platform for metal chelating natural products that act as metallophores, ion buffers or sequestering agents. The detection of cation and oxoanion complexing ligands is facilitated by the identification of unique isotopic signatures created by the application of isotopically pure metals. Figure © Deicke, M., Mohr, J. F., Bellenger, J. P., Wichard, T. (2014) Metallophore mapping in complex matrices by metal isotope coded profiling of organic ligands. Analyst, 23, 6096 - 6099.External link