Project description:Time series microarray analysis on the photosynthetic ciliate was conducted using an oligochip containing 15,654 genes designed from Teleaulax amphioxeia ESTs
Project description:Kleptoplastic mixotrophic species of the genus Dinophysis are cultured by feeding with the ciliate Mesodinium rubrum, itself a kleptoplastic mixotroph, that in turn feeds on cryptophytes of the Teleaulax/Plagioselmis/Geminigera (TPG) clade. Optimal culture media for phototrophic growth of D. acuminata and D. acuta from the Galician Rías (northwest Spain) and culture media and cryptophyte prey for M.rubrum from Huelva (southwest Spain) used to feed Dinophysis, were investigated. Phototrophic growth rates and yields were maximal when D. acuminata and D. acuta were grown in ammonia-containing K(-Si) medium versus f/2(-Si) or L1(-Si) media. Dinophysis acuminata cultures were scaled up to 18 L in a photobioreactor. Large differences in cell toxin quota were observed in the same Dinophysis strains under different experimental conditions. Yields and duration of exponential growth were maximal for M. rubrum from Huelva when fed Teleaulax amphioxeia from the same region, versus T. amphioxeia from the Galician Rías or T. minuta and Plagioselmis prolonga. Limitations for mass cultivation of northern Dinophysis strains with southern M. rubrum were overcome using more favorable (1:20) Dinophysis: Mesodinium ratios. These subtleties highlight the ciliate strain-specific response to prey and its importance to mass production of M. rubrum and Dinophysis cultures.
Project description:In the present study, the susceptibility of the purple pigmented photosynthetic alphaproteobacterium Rhodospirillum rubrum S1H to gamma irradiation was investigated and its molecular response was characterised by means of gene expression analysis. R. rubrum S1H appears to be about 4 times more sensitive than the model strain Escherichia coli MG1655 to cobalt-60 gamma irradiation. Whole genome response of R. rubrum to 25 Gy revealed the common expression of SOS response related genes in both rich and minimal media. Quantitative expression of the lexA gene was followed after various recovery time following gamma irradiation and showed differential gene expression pattern between minimal and rich medium. This work paves the way for forthcoming molecular studies on the effect of ionizing radiation on R. rubrum S1H and the other MELiSSA strains. Keywords: Rhodospirillum rubrum; ionizing radiation tolerance; microarray; quantitative PCR.
Project description:Predator-prey interactions of planktonic protists are fundamental to plankton dynamics and include prey selection, detection, and capture as well as predator detection and avoidance. Propulsive, morphology-specific behaviors modulate these interactions and therefore bloom dynamics. Here, interactions between the mixotrophic, harmful algal bloom (HAB) dinoflagellate Dinophysis acuminata and its ciliate prey Mesodinium rubrum were investigated through quantitative microvideography using a high-speed microscale imaging system (HSMIS). The dinoflagellate D. acuminata is shown to detect its M. rubrum prey via chemoreception while M. rubrum is alerted to D. acuminata via mechanoreception at much shorter distances (89?±?39??m versus 41?±?32 ?m). On detection, D. acuminata approaches M. rubrum with reduced speed. The ciliate M. rubrum responds through escape jumps that are long enough to detach its chemical trail from its surface, thereby disorienting the predator. To prevail, D. acuminata uses capture filaments and/or releases mucus to slow and eventually immobilize M. rubrum cells for easier capture. Mechanistically, results support the notion that the desmokont flagellar arrangement of D. acuminata lends itself to phagotrophy. In particular, the longitudinal flagellum plays a dominant role in generating thrust for the cell to swim forward, while at other times, it beats to supply a tethering or anchoring force to aid the generation of a posteriorly-directed, cone-shaped scanning current by the transverse flagellum. The latter is strategically positioned to generate flow for enhanced chemoreception and hydrodynamic camouflage, such that D. acuminata can detect and stealthily approach resting M. rubrum cells in the water column.