Roccella species constitute interesting models to address questions regarding lichen metabolite diversity across taxonomic, ecological and geographic gradients. Indeed, owing to their wide distribution, their taxonomic diversity and the narrow ecological niche they occupy, Roccella species are good candidates to study the drivers of lichen chemistry. This study focuses on the chemical profiling of five species: R. applanata, R. belangeriana, R. fuciformis, R. montagnei and R. phycopsis. These five species were sampled in a rather narrow longitudinal range (1°51′W to 47°17′E) covering the Eastern Atlantic and Western Indian Ocean areas along an extended latitudinal range (48°49′N to 22°23′S). High Pressure Liquid Chromatography (HPLC) analysis followed by mass spectrometry of 31 Roccella thalli revealed a number of interesting patterns through a multivariate (PCA) analysis, including the first detailed chemical profiles for two species from the Scattered Islands: R. applanata and R. belangeriana. Metabolite segregation amongst all studied Roccella species, including R. montagnei and R. belangeriana, gave some insight into the taxonomy of the latter two species, which we interpret as separate species. An additional analysis focusing on R. montagnei samples revealed chemical differences along both a latitudinal and ecological gradient (from Europa Island to São Tomé and Príncipe). Three mass spectra databases were built to dereplicate the ions, which gave an overview of the factors that could drive quantitative and qualitative metabolite composition in lichens. Additionally, several new Roccella species records are reported for the Scattered Islands, as well as São Tomé and Príncipe.

The comprehension of microbial interactions is one of the key challenges in marine microbial ecology. This study focused on exploring chemical interactions between the toxic dinoflagellate Prorocentrum lima and a filamentous fungal species, Aspergillus pseudoglaucus, which has been isolated from the microalgal culture. Such interspecies interactions are expected to occur even though they were rarely studied. Here, a co-culture system was designed in a dedicated microscale marine-like condition. This system allowed to explore microalgal-fungal physical and metabolic interactions in presence and absence of the bacterial consortium. Microscopic observation showed an unusual physical contact between the fungal mycelium and dinoflagellate cells. To delineate specialized metabolome alterations during microalgal-fungal co-culture metabolomes were monitored by highperformance liquid chromatography coupled to high-resolution mass spectrometry. In-depth multivariate statistical analysis using dedicated approaches highlighted (1) the metabolic alterations associated with microalgal-fungal co-culture, and (2) the impact of associated bacteria in microalgal metabolome response to fungal interaction. Unfortunately, only a very low number of highlighted features were fully characterized. However, an up-regulation of the dinoflagellate toxins okadaic acid and dinophysistoxin 1 was observed during co-culture in supernatants. Such results highlight the importance to consider microalgal-fungal interactions in the study of parameters regulating toxin production.

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.