Aproximaciones moleculares a la identificación de especies del género Dinophysis y al análisis de las interrelaciones tróficas de D. acuta y sus presas

Resumen

Several dinoflagellate species of the genus Dinophysis Ehrenberg produce potent lipophilic shellfish toxins (okadaic acid, its derivatives and the pectenotoxins) and pose a major threat to shellfish aquaculture in the world, leading to large economic losses. Dinophysis species have a complicated life cycle, with several intermediate forms, with different toxic potentials, that can be confuse to identify. The identification of Dinophysis species is carried out by specialized personnel and is a crucial task in harmful algae monitoring programmes intended to prevent Diarrhetic Shellfish Poisoning (DSP) syndrome. Toxicity varies among morphologically similar species, and a precise identification is needed for early warning systems. Molecular techniques using DNA sequences offer means to precisely identify and detect the potentially toxic species. In this study, the potential of different regions of the rRNA operon and two mitochondrial genes (mt cox1 and cob) was explored to discriminate among Dinophysis species associated with DSP events (field isolates and cultures) from Galicia waters, one of the bigger mussels producers in the world. Our results reveal that the taxonomic assignment of Dinophysis species using rRNA molecular markers is a difficult task due to extremely low interspecific variability of the nuclear ribosomal genes and intergenic regions. However we have shown that mitochondrial cox1 gene is a more suitable marker for Dinophysis species based on its specificity and higher resolution. The carbohydrate composition of the cell surface was evaluated with FITC- conjugated lectins in several Dinophysis species from two geographical locations, Vigo and Huelva, as an alternative to molecular DNA-based identification. Our result shown that this technique have the potential to discriminate between species, and provide a new tool to complement standard microscopic identification. The toxic marine dinoflagellate species of the genus Dinophysis are obligate mixotrophs that require feeding on the ciliate Mesodinium rubrum and light to achieve growth. It is now well known that they harbor plastids of cryptophyte origin, particularly of the genus Teleaulax, Plagioselmis or Geminigera group (TPG clade). Nevertheless, whether these plastids are permanent, or periodically acquired from M. rubrum prey, is still controversial. The origin of plastids from Dinophysis acuta Ehrenberg, one of the main agents of DSP outbreaks in Western Europe, was investigated here. Cross feeding-starvation experiments were carried out with cultures of D. acuta using M. rubrum as prey, the latter fed with two cryptophyte species, Teleaulax amphioxeia and Teleaulax gracilis, belonging to the TPG clade, in addition to Falcomonas sp. and Hemiselmis sp. The fate of cryptophyte plastids transferred to D. acuta through its ciliate prey was investigated using the plastid psbA gene as a tracer.