Bacteria in Ostreococcus tauri cultures – friends, foes or hitchhikers?

Abstract

Marine phytoplankton produce half of the oxygen we breathe and their astounding diversity is just starting to be unraveled. Many microbial phytoplankton are thought to be phototrophic, depending solely on inorganic sources of carbon and minerals for growth rather than preying on other planktonic cells. However, there is increasing evidence that symbiotic associations, to a large extent with bacteria, are required for vitamin or nutrient uptake for many eukaryotic microalgae. Here, we use in silico approaches to look for putative symbiotic interactions by analysing the gene content of microbial communities associated with 13 different Ostreococcus tauri (Chlorophyta, Mamilleophyceae) cultures sampled from the Mediterranean Sea. While we find evidence for bacteria in all cultures, there is no ubiquitous bacterial group, and the most prevalent group, Flavobacteria, is present in 10 out of 13 cultures. Among seven of the microbiomes, we detected genes predicted to encode type 3 secretion systems (T3SS, in 6/7 microbiomes) and/or putative type 6 secretion systems (T6SS, in 4/7 microbiomes). Phylogenetic analyses show that the corresponding genes are closely related to genes of systems identified in bacterial-plant interactions, suggesting that these T3SS might be involved in cell-to-cell interactions with O. tauri.

Microbial dynamics during harmful dinoflagellate Ostreopsis cf. ovata growth: Bacterial succession and viral abundance pattern

“…Overall, in this study, the co‐dominance of Oceanicaulis and Dinoroseobacter phylotypes (closely related to Oceanicaulis alexandrii and Dinoroseobacter shibae at 96% and 99% 16S rRNA gene sequence similarity, respectively; Table ) at exponential and late stationary algal growth phases reflects their high metabolic plasticity, considering the deep differences in terms of inorganic nutrient concentrations and organic matter quality and availability between the two distinct phases. Oceanicaulis representatives have been retrieved from several marine algal cultures ( Alexandrium tamarense , Strompl, ; Emiliania huxleyi , Zabeti, Bonin, Volkman, Guasco, & Rontani, ; Eutreptiella sp., Kuo & Lin, ; Ostreococcus tauri , Abby, Touchon, De Jode, Grimsley, & Piganeau, ), and genes and regulons involved in biosynthesis pathways of B vitamins (i.e., B 1 , B 7 , and B 12 ) have been detected in Oceanicaulis phylotypes (Oh et al., ). Additionally, the versatile chemoheterotrophic metabolism reported for this genus (Chen, Sheu, Chen, Wang, & Chen, ; Oh et al., ; Strompl, ) also encompasses efficient phosphate uptake capacity in carbon‐limited medium and inorganic nutrient depleted conditions through high‐affinity phosphate transporters located in the prosthecae (McAdams, ; Oh et al., ).…”

“…ovata exponential growth phase. Roseovarius ‐affiliated phylotypes have been recovered from different cultured marine algal species (Biebl et al., ; Onda et al., ), also concurrently with Oceanicaulis (Abby et al., ; Kuo & Lin, ) and Fabibacter relatives (Green, Echavarri‐Bravo, Brennan, & Hart, ), and in association with toxic dinoflagellate blooms (Vanucci, Guidi, et al., ; Yang et al., ). Metagenomic and biochemical analyses highlighted the large metabolic portfolio of Roseovarius (Bruns et al., ; Riedel et al., ), including synthesis of dual nature compounds (i.e., algal growth promoting and algicidal ones; Ziesche et al., ).…”

Niche-based assembly of bacterial consortia on the diatom Thalassiosira rotula is stable and reproducible

“…Indeed, several recent microbiome studies of diverse phytoplankton suggest that marine and fresh water phytoplankton harbor unique bacterial consortia which are consistent within phytoplankton species and across temporal scales [16][17][18][19]. Yet, some phytoplankton do not harbor a core set of associated bacteria [20]. In these cases, the sampling time and location are suggested to be more decisive factors determining the associated microbiome than phytoplankton species affiliation [21].…”

Cultured Ostreococcus is cobalamin-independent

“…The utility of METE as a positive selection marker relies on a cobalamin-dependent Ostreococcus transformation recipient. RCC614 is a representative co-culture of Ostreococcus and various phycosphere-associated marine bacteria (Abby et al, 2014;Lupette et al, 2016). The bacteria may supply biotin, cobalamin, and methionine to the Ostreococcus phycosphere.…”