A dual-species co-cultivation system to study the interactions between Roseobacters and dinoflagellates

Abstract

Some microalgae in nature live in symbiosis with microorganisms that can enhance or inhibit growth, thus influencing the dynamics of phytoplankton blooms. In spite of the great ecological importance of these interactions, very few defined laboratory systems are available to study them in detail. Here we present a co-cultivation system consisting of the toxic phototrophic dinoflagellate Prorocentrum minimum and the photoheterotrophic alphaproteobacterium Dinoroseobacter shibae. In a mineral medium lacking a carbon source, vitamins for the bacterium and the essential vitamin B12 for the dinoflagellate, growth dynamics reproducibly went from a mutualistic phase, where both algae and bacteria grow, to a pathogenic phase, where the algae are killed by the bacteria. The data show a “Jekyll and Hyde” lifestyle that had been proposed but not previously demonstrated. We used RNAseq and microarray analysis to determine which genes of D. shibae are transcribed and differentially expressed in a light dependent way at an early time-point of the co-culture when the bacterium grows very slowly. Enrichment of bacterial mRNA for transcriptome analysis was optimized, but none of the available methods proved capable of removing dinoflagellate ribosomal RNA completely. RNAseq showed that a phasin encoding gene (phaP1) which is part of the polyhydroxyalkanoate (PHA) metabolism operon represented approximately 10% of all transcripts. Five genes for aerobic anoxygenic photosynthesis were down-regulated in the light, indicating that the photosynthesis apparatus was functional. A betaine-choline-carnitine-transporter (BCCT) that may be used for dimethylsulfoniopropionate (DMSP) uptake was the highest up-regulated gene in the light. The data suggest that at this early mutualistic phase of the symbiosis, PHA degradation might be the main carbon and energy source of D. shibae, supplemented in the light by degradation of DMSP and aerobic anoxygenic photosynthesis.

Current Knowledge and Recent Advances in Marine Dinoflagellate Transcriptomic Research

“…A similar pattern of this unique symbiosis was reported in the marine coccolithophore Emiliania huxleyi with bacteria Phaeobacter gallaeciensis, and a "Jekyll and Hyde" lifestyle has been proposed for the unique symbiosis between bacteria from clade Roseobacter with marine algae [108]. Transcriptomics analysis of the bacterium D. shibae revealed that quorum sensing, CtrA phosphorelay and flagella biosynthesis genes were involved in this mutualistic turned parasitic relationship, as these genes were upregulated during the early pathogenic phase and downregulated in the late pathogenic phase [107]. To date, transcriptomic studies regarding bacteria-dinoflagellates symbiosis remain limited, most probably due to the difficulty in obtaining and growing axenic culture.…”

“…Another transcriptomic study revealed an interesting relationship between alphaproteobacterium Dinoroseobacter shibae and P. minimum, where the symbiotic relationship during co-culture of D. shibae axenic culture and P. minimum starts a mutualistic phase where both dinoflagellates and bacteria were helping each other and a pathogenic phase where aged dinoflagellates are killed by this bacterium [107]. A similar pattern of this unique symbiosis was reported in the marine coccolithophore Emiliania huxleyi with bacteria Phaeobacter gallaeciensis, and a "Jekyll and Hyde" lifestyle has been proposed for the unique symbiosis between bacteria from clade Roseobacter with marine algae [108].…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…This process seems to be enhanced by surface association (150,151,173,762,(778)(779)(780) and may enhance ATP production, active transport, motility, and cell growth yield on available organic matter (272,779). Some MRC bacteria synthesize and store poly-␤-hydroxyalkanoates when carbon and energy resources are available but inorganic nutrients are limiting (781,782), which may enhance bacterial viability via poly-␤-hydroxyalkanoate catabolism when other sources of organic substrates are scarce (594). Some MRC bacteria also carry out lithotrophic sulfur oxidation to conserve additional energy (783,784), which may be explored to enhance anaplerotic CO 2 fixation, growth, and survival (761,785).…”

Dynamic metabolic exchange governs a marine algal-bacterial interaction

“…Various types of phytoplankton were shown to have both mutualistic and antagonistic interactions with bacteria (Amin et al, 2015; Miller and Belas, 2004; Miller et al, 2004; Wang et al, 2014; Durham et al, 2015). In addition, the possible role of algicidal bacteria in the ocean has been examined and discussed (Mayali and Azam, 2004; Harvey et al, 2016).…”