A new glance at the chemosphere of macroalgal-bacterial interactions: In situ profiling of metabolites in symbiosis by mass spectrometry

Marine Vallet; Filip Kaftan; Veit Grabe; Fatemeh Ghaderiardakani; Simona Fenizia; Aleš Svatoš; Georg Pohnert; Thomas Wichard

doi:10.3762/bjoc.17.91

A new glance at the chemosphere of macroalgal-bacterial interactions: In situ profiling of metabolites in symbiosis by mass spectrometry

Beilstein J Org Chem. 2021 May 19:17:1313-1322. doi: 10.3762/bjoc.17.91. eCollection 2021.

Authors

Marine Vallet¹, Filip Kaftan², Veit Grabe³, Fatemeh Ghaderiardakani⁴, Simona Fenizia^{4

5}, Aleš Svatoš², Georg Pohnert^{1

4

6}, Thomas Wichard⁴

Affiliations

¹ Research Group Phytoplankton Community Interactions, Max Planck Institute for Chemical Ecology, Jena, Germany.
² Research Group Mass Spectrometry/Proteomics, Max Planck Institute for Chemical Ecology, Jena, Germany.
³ Research Group Olfactory Coding, Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology, Jena, Germany.
⁴ Institute for Inorganic and Analytical Chemistry, Friedrich Schiller University Jena, Germany.
⁵ Max Planck Institute for Chemical Ecology, Jena, Germany.
⁶ Microverse Cluster, Friedrich Schiller University Jena, Germany.

Abstract

Symbiosis is a dominant form of life that has been observed numerous times in marine ecosystems. For example, macroalgae coexist with bacteria that produce factors that promote algal growth and morphogenesis. The green macroalga Ulva mutabilis (Chlorophyta) develops into a callus-like phenotype in the absence of its essential bacterial symbionts Roseovarius sp. MS2 and Maribacter sp. MS6. Spatially resolved studies are required to understand symbiont interactions at the microscale level. Therefore, we used mass spectrometry profiling and imaging techniques with high spatial resolution and sensitivity to gain a new perspective on the mutualistic interactions between bacteria and macroalgae. Using atmospheric pressure scanning microprobe matrix-assisted laser desorption/ionisation high-resolution mass spectrometry (AP-SMALDI-HRMS), low-molecular-weight polar compounds were identified by comparative metabolomics in the chemosphere of Ulva. Choline (2-hydroxy-N,N,N-trimethylethan-1-aminium) was only determined in the alga grown under axenic conditions, whereas ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid) was found in bacterial presence. Ectoine was used as a metabolic marker for localisation studies of Roseovarius sp. within the tripartite community because it was produced exclusively by these bacteria. By combining confocal laser scanning microscopy (cLSM) and AP-SMALDI-HRMS, we proved that Roseovarius sp. MS2 settled mainly in the rhizoidal zone (holdfast) of U. mutabilis. Our findings provide the fundament to decipher bacterial symbioses with multicellular hosts in aquatic ecosystems in an ecologically relevant context. As a versatile tool for microbiome research, the combined AP-SMALDI and cLSM imaging analysis with a resolution to level of a single bacterial cell can be easily applied to other microbial consortia and their hosts. The novelty of this contribution is the use of an in situ setup designed to avoid all types of external contamination and interferences while resolving spatial distributions of metabolites and identifying specific symbiotic bacteria.

Keywords: AP-SMALDI; Ulva; algae; ectoine; high-resolution mass spectrometry; holobiont; marine bacteria; mass spectrometry imaging.

Grants and funding

SF was funded by the International Max Planck Research School Exploration of Ecological Interactions with Molecular Techniques. This work was supported by an MPG Fellowship awarded to GP and by the Deutsche Forschungsgemeinschaft through Grant No. SFB 1127/2 ChemBioSys–239748522 (GP, TW) and within the framework of the priority program (SPP 1158) "Antarctic Research with comparative investigations in Arctic ice areas" under the project number #424256657 (FG, TW).