Ciguatera fish poisoning is a food borne disease that is increasing its prevalence in tropical areas. The causative organisms are marine dinoflagellates of the genus Gambierdiscus, some species of which produce the neurotoxins ciguatoxins, which bioaccumulate in fish. Determining the genetic basis for the production of these polyketide toxins will be key to understanding their ecology, evolution and pharmacology. However, due to their large genomes (0.5-40 x the size of the human haploid genome) and complex genetic processes, it is currently very difficult to sequence dinoflagellate genomes.
Here, we focused on sequencing the transcriptomes of two highly toxic strains of Gambierdiscus polynesiensis (as verified by LC-MS), as well as a non-toxic strain of G. carpenteri. The transcriptomes were assembled and de novo annotated. Polyketide related genes were investigated using hmmr searches and compared to known dinoflagellate polyketide and fatty acid synthase genes. Phylogenetic analysis of the polyketide active domains shows the complex evolutionary relationship of polyketide synthases involved in cell function and toxin production.
This work is instrumental on the road of pin pointing which polykrtide synthases are responsible for ciguatoxins production and designing an early detection system for ciguatera outbreaks.