Perkinsiella amoebae-like enclosymbionts of Neoparamoeba spp., relatives of the kinetoplastid Ichthyobodo

Eukaryotic endosymbionts ("parasomes") were studied in Neoparamoeba strains of different origin including two strains of N. pemaquidensis (Page, 1970), the agent of amoebic gill disease (AGD). Comparative study of the endosymbionts revealed their mutual ultrastructural similarity and also similarity with the endosymbiont Perkinsiella amoebae Hollande, 1980 described from Janickina chaetognathi and J. pigmentifera. Morphological features supported Hollande's hypothesis on the kinetoplastid origin of A amoebae but the first conclusive results were obtained in this study using marker genes. The recognition of euglenozoan spliced leader RNA (SL RNA) gene sequences in the genomic DNA of endosymbionts from five Neoparamoeba strains together with the acquisition of one SSU RNA gene sequence allowed us to specify the relationship of the endosymbionts under study with kinetoplastids. Phylogenetic analyses of SSU rRNA gene sequence data currently available revealed close relationship of the first sequenced Perkinsiella amoebae-like organism with Ichthyobodo necator. Sequence comparisons disclosed that A amoebae-like organisms possess SL RNA genes with a significant level of divergence from other kinetoplastids. However, the sequences are more closely related to kinetoplastids and Diplonema spp. than to euglenids. Three types of the SL RNA gene sequences obtained from P. amoebae-like organisms were congruent with phylogeny of their Neoparamoeba host strains.