Thomas Wichard

About Thomas Wichard:

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.

SEEK ID: https://data.chembiosys.de/people/9

Location:  Germany

ORCID: https://orcid.org/0000-0003-0061-4160

Joined: 2nd Oct 2015

Expertise: Marine Science, Analytical Chemistry, Biochemistry, Algal Genetics, Chemical Ecology

Tools: Molecular Biology, LC/MS, GC/MS, Bioassays guided purification, Metabolomics

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C5

Metallophores as Mediators for Metal Cycling: Development of Libraries for Metal Ion Buffering and as Redox Carriers as well as Profiling of Metallophores

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A1

Identification of Novel Infochemicals and their Biosynthetic Pathways Mediating the Cross Kingdom Communication between Ulva and its Associated Bacteria

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Frankobactin Metallophores Produced by Nitrogen-Fixing Frankia Actinobacteria Function in Toxic Metal Sequestration.
B05

Abstract (Expand)

A series of new metallophores, referred to as frankobactins, were extracted from cultures of the symbiotic and nitrogen-fixing actinobacterium Frankia sp. CH37. Structure elucidation revealed a … 2-hydroxyphenyl-substituted oxazoline core and a chain composed of five proteinogenic and nonproteinogenic amino acids, suggesting nonribosomal peptide synthesis as the biosynthetic origin. By whole-genome sequencing, bioinformatic analysis, and comparison with other Frankia strains, the genetic locus responsible for the biosynthesis was detected. Spectrophotometric titration of frankobactin with Fe(III) and Cu(II) and mass spectrometry established the 1:1 (metal:frankobactin) coordination. Uptake experiments suggested that frankobactin A1 (1) did not serve to recruit iron, but to detoxify Cu(II). As frankobactin A1 prevents the cellular entry of Cu(II), it could play a crucial role in the symbiosis of Frankia sp. and its host in the reclamation of copper-contaminated soil.

Authors: J. F. Mohr, F. Baldeweg, M. Deicke, C. F. Morales-Reyes, D. Hoffmeister, T. Wichard

Date Published: 23rd Apr 2021

Publication Type: Journal

Rhizobactin B is the preferred siderophore by a novel Pseudomonas isolate to obtain iron from dissolved organic matter in peatlands.
C5

Abstract (Expand)

Bacteria often release diverse iron-chelating compounds called siderophores to scavenge iron from the environment for many essential biological processes. In peatlands, where the biogeochemical cycle … of iron and dissolved organic matter (DOM) are coupled, bacterial iron acquisition can be challenging even at high total iron concentrations. We found that the bacterium Pseudomonas sp. FEN, isolated from an Fe-rich peatland in the Northern Bavarian Fichtelgebirge (Germany), released an unprecedented siderophore for its genus. High-resolution mass spectrometry (HR-MS) using metal isotope-coded profiling (MICP), MS/MS experiments, and nuclear magnetic resonance spectroscopy (NMR) identified the amino polycarboxylic acid rhizobactin and a novel derivative at even higher amounts, which was named rhizobactin B. Interestingly, pyoverdine-like siderophores, typical for this genus, were not detected. With peat water extract (PWE), studies revealed that rhizobactin B could acquire Fe complexed by DOM, potentially through a TonB-dependent transporter, implying a higher Fe binding constant of rhizobactin B than DOM. The further uptake of Fe-rhizobactin B by Pseudomonas sp. FEN suggested its role as a siderophore. Rhizobactin B can complex several other metals, including Al, Cu, Mo, and Zn. The study demonstrates that the utilization of rhizobactin B can increase the Fe availability for Pseudomonas sp. FEN through ligand exchange with Fe-DOM, which has implications for the biogeochemical cycling of Fe in this peatland.

Authors: S. Kugler, R. E. Cooper, J. Boessneck, K. Kusel, T. Wichard

Date Published: 7th Oct 2020

Publication Type: Journal

Macroalgal-bacterial interactions: identification and role of thallusin in morphogenesis of the seaweed Ulva (Chlorophyta).
A1

Abstract (Expand)

Macroalgal microbiomes have core functions related to biofilm formation, growth, and morphogenesis of seaweeds. In particular, the growth and development of the sea lettuce Ulva spp. (Chlorophyta) … depend on bacteria releasing morphogenetic compounds. Under axenic conditions, the macroalga Ulva mutabilis develops a callus-like phenotype with cell wall protrusions. However, co-culturing with Roseovarius sp. (MS2) and Maribacter sp. (MS6), which produce various stimulatory chemical mediators, completely recovers morphogenesis. This ecological reconstruction forms a tripartite community which can be further studied for its role in cross-kingdom interactions. Hence, our study sought to identify algal growth- and morphogenesis-promoting factors (AGMPFs) capable of phenocopying the activity of Maribacter spp. We performed bioassay-guided solid-phase extraction in water samples collected from U. mutabilis aquaculture systems. We uncovered novel ecophysiological functions of thallusin, a sesquiterpenoid morphogen, identified for the first time in algal aquaculture. Thallusin, released by Maribacter sp., induced rhizoid and cell wall formation at a concentration of 11 pmol l-1. We demonstrated that gametes acquired the iron complex of thallusin, thereby linking morphogenetic processes with intracellular iron homeostasis. Understanding macroalgae-bacteria interactions permits further elucidation of the evolution of multicellularity and cellular differentiation, and development of new applications in microbiome-mediated aquaculture systems.

Authors: T. Alsufyani, G. Califano, M. Deicke, J. Grueneberg, A. Weiss, A. H. Engelen, M. Kwantes, J. F. Mohr, J. F. Ulrich, T. Wichard

Date Published: 11th Jun 2020

Publication Type: Journal

Metallophore profiling of nitrogen-fixing Frankia spp. to understand metal management in the rhizosphere of actinorhizal plants.
C5

Abstract (Expand)

Frankia spp. are widespread nitrogen-fixing soil bacteria, which often live in symbiosis with a broad range of hosts. Metal homeostasis plays a crucial role in the success of the symbiosis regarding … the acquisition of essential trace metals and detoxification of potentially toxic elements. We have hypothesised that Frankia releases many organic ligands with a broad spectrum of affinity for essential and toxic metals. We coined the term 'ligandosphere' to describe the entirety of excreted metal complexing agents and ligands derived from the dissolved organic matter. Using metal isotope-coded profiling (MICP); metallophores of physiological important and toxic trace metals were identified by the addition of stable metal isotope pairs such as 54Fe/58Fe, 63Cu/65Cu, 66Zn/68Zn or 95Mo/98Mo. Liquid chromatography coupled to a mass spectrometer revealed strong variations of the metallophore profile in between the 14 test-strains. In total, about 83 organic ligands were identified as binding to one of the tested metals. The predicted sum formula of the major Fe binding ligands and MS/MS experiments suggested that several metallophore candidates have a similar molecular backbone. Growth experiments with a hyper-producer of metallophores revealed a positive relationship between metallophore production and the concentration of Cu in the growth medium. The present study provides the first comprehensive overview of the complexity of Frankia's ligandosphere. It opens a path to a deeper understanding of mechanisms that regulate metal homeostasis in frankiae. Deciphering these mechanisms is important since the fitness of actinorhizal plants and their potential in ecological restoration relies heavily on their symbiosis with frankiae.

Authors: M. Deicke, J. F. Mohr, S. Roy, P. Herzsprung, J. P. Bellenger, T. Wichard

Date Published: 17th Apr 2019

Publication Type: Journal

Algae induce siderophore biosynthesis in the freshwater bacterium Cupriavidus necator H16.
A1, C5

Abstract (Expand)

Cupriachelin is a photoreactive lipopeptide siderophore produced by the freshwater bacterium Cupriavidus necator H16. In the presence of sunlight, the iron-loaded siderophore undergoes photolytic … cleavage, thereby releasing solubilized iron into the environment. This iron is not only available to the siderophore producer, but also to the surrounding microbial community. In this study, the cupriachelin-based interaction between C. necator H16 and the freshwater diatom Navicula pelliculosa was investigated. A reporter strain of the bacterium was constructed to study differential expression levels of the cupriachelin biosynthesis gene cucJ in response to varying environmental conditions. Not only iron starvation, but also culture supernatants of N. pelliculosa were found to induce cupriachelin biosynthesis. The transcription factors involved in this differential gene expression were identified using DNA-protein pulldown assays. Besides the well-characterized ferric uptake regulator, a two-component system was found to tune the expression of cupriachelin biosynthesis genes in the presence of diatom supernatants.

Authors: C. Kurth, I. Wasmuth, T. Wichard, G. Pohnert, M. Nett

Date Published: 27th Nov 2018

Publication Type: Journal

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