Phylogeny, Morphology, and Metabolic and Invasive Capabilities of Epicellular Fish Coccidium Goussia janae.

To fill the knowledge gap on the biology of the fish coccidian Goussia janae, RNA extracted from exogenously sporulated oocysts was sequenced. Analysis by Trinity and Trinotate pipelines showed that 84.6% of assembled transcripts share the highest similarity with Toxoplasma gondii and Neospora caninum. Phylogenetic and interpretive analyses from RNA-seq data provide novel insight into the metabolic capabilities, composition of the invasive machinery and the phylogenetic relationships of this parasite of cold-blooded vertebrates with other coccidians. This allows re-evaluation of the phylogenetic position of G. janae and sheds light on the emergence of the highly successful obligatory intracellularity of apicomplexan parasites. G. janae possesses a partial glideosome and along with it, the metabolic capabilities and adaptions of G. janae might provide cues as to how apicomplexans adjusted to extra- or intra-cytoplasmic niches and also to become obligate intracellular parasites. Unlike the similarly localized epicellular Cryptosporidium spp., G. janae lacks the feeder organelle necessary for directly scavenging nutrients from the host. Transcriptome analysis indicates that G. janae possesses metabolic capabilities comparable to T. gondii. Additionally, this enteric coccidium might also access host cell nutrients given the presence of a recently identified gene encoding the molecular sieve at the parasitophorous vacuole membrane.