Tetraselmis suecicaF&M-M33 phycosphere: associated bacteria and exo-metabolome characterisation

Algae and bacteria establish complex relationships reciprocally influencing their growth. Associated bacterial communities alter microalgae metabolism and physiology, affecting biomass yield and quality. In this study, 203 bacterial isolates (33 different genera), recovered fromTetraselmis suecicaF&M-M33 cultures, were identified and phenotypically characterized in relation to the microalgal growth-promoting (MGP) features of indol-3-acetic acid (IAA) and siderophore production. IAA production was observed in 30 isolates belonging to 10 genera, whilst siderophore production was observed in 12 isolates belonging to nine genera, indicating that bacteria which are phylogenetically different within the phycosphere community may contribute in similar ways to boosting algal growth. Moreover, strains belonging to a single genus (e.g.Bacillus, Muricauda, LabrenziaandAmorphus) showed different MGP features, but none of these isolates were capable of producing both growth-promoting factors. Twenty-two selected strains were further tested in co-culture assays to evaluate their effect onT. suecicaF&M-M33 growth; four induced an increase in microalgal productivity. The exo-metabolome ofT. suecicaF&M-M33 cultures, either axenically or when co-cultured with eitherVitellibacterstrain AAD2 orSphingopyxis flavimarisstrain AG5, was determined using a non-targeted metabolomics approach using an Ultra High Performance Liquid Chromatography (UHPLC) system. This allowed for the detection of 133 entities (small chemical molecules, e.g. metabolites), of which 84 were identified. Most of the entities were common in all three cultures, showing that theT. suecicaF&M-M33 phycosphere was rich in small peptides and organic acids, and a high number of terpenes were also observed. Seventeen entities were culture-specific, suggesting that they were directly related to microalgae-bacteria interactions.

Automated summary

Algae and bacteria establish complex relationships that reciprocally influence their growth. Different bacterial isolates from the phycosphere community may contribute in similar ways to boosting algal growth. Bacteria with growth-promoting features can alter microalgae metabolism and physiology, affecting biomass yield and quality.