Deciphering microbiome impacts on fungal-microalgal interaction in a marine environment using metabolomics

The comprehension of microbial interactions is one of the key challenges in microbial ecology. The present study focuses on studying the chemical interaction between the toxic dinoflagellate Prorocentrum lima PL4V strain and associated fungal strains (two Penicillium sp. strains and three Aspergillus sp) among which the Aspergillus pseudoglaucus strain MMS1589 was selected for further co-culture experiment. Such rarely studied interaction (fungal-microalgal) was explored in axenic and non-axenic conditions, in a dedicated microscale marine environment (hybrid solid/liquid conditions), to delineate specialized metabolome alteration in relation to the P. lima and A. pseudoglaucus co-culture in regard to the presence of their associated bacteria. Such alteration was monitored by high-performance liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS). In-depth analysis of the resulting data highlighted (1) the chemical modification associated to fungal-microalgal co-culture, and (2) the impact of associated bacteria in microalgal resilience to fungal interaction. Even if only a very low number of highlighted metabolites were fully characterised due to the poor chemical investigation of the studied species, a clear co-culture induction of the dinoflagellate toxins okadaic acid and dinophysistoxin 1 was observed. Such results highlight the importance to consider microalgal microbiome to study parameters regulating toxin production. Finally, a microscopic observation showed an unusual physical interaction between the fungal mycelium and the dinoflagellates. ### Competing Interest Statement The authors have declared no competing interest.