Functional and phylogenetic analysis of the core transcriptome of Ochromonadales

Background Most protist lineages consist of members with diverging features e.g. different modes of nutrition and adaptations for life in different habitat types and climatic zones. The nutritional mode is particularly variable in chrysophytes and they are therefore an excellent model group to study the core genes and metabolic pathways of a functionally diverse lineage. The objective of our study is the identification of the joint genetic repertoire expressed in closely related chrysophytes as well as the extent of variation on species and strain level. Therefore, we investigated the transcriptomes of six strains belonging to four species of Ochromonadales. We performed analyses on metabolic pathway level as well as on sequence level. Results We could identify 1,574 core genes shared between all six investigated strains of Ochromonadales. Most of these core genes were affiliated with the primary metabolism. Phylogenetic analysis of 166 protein-coding core genes supported a close relation of Poteriospumella lacustris and Poterioochromonas malhamensis and resolved for more than 50% of investigated genes the relationship of strains affiliated with the species P. lacustris. Further, we found diverging phylogenetic patterns for genes interacting with the environment. Conclusions In Ochromonadales, a functionally diverse lineage, the core transcriptome represents only a minor part of the individual transcriptomes. But this small fraction of genes comprises the basal metabolism essential for life in several protist lineages. Phylogenetic analyses of these genes indicate a similar degree of conservation as observed for genes coding for ribosomal proteins.