Poteriospumella lacustris strain:JBNZ41 Genome sequencing and assembly

Background: Poteriospumella lacustris is a freshwater protist belonging to the Chrysophyceae. Its mode of nutrition is heterotrophic, however, it evolved from a phototrophic progenitor by reducing its genome and plastome. We examined three strains from different geographic regions (New Zealand: JBNZ41, China: JBC07and Austria: JBM10) to gain insights into the diversification mechanism, genome structure and intraspecific genome variation within the Chrysophyceae.Results: The three strains were sequenced with the Illumina and PacBio platforms and subsequently assembled to draft genomes with a size of 49-55 Mb. Each strain contains between 16,000 and 19,000 genes, of which about 8,000 genes could be identified and assigned to functional groups. At least 68% of these genes were shared in all three species. We could show that gene mutations occur in different functional groups withvarying frequencies. Additionally, the gene density ranges from 310-370 Mb -1 and most surprisingly the ploidy differs between the strains (JBM10: diploid, JBC07: triploid, JBNZ41: tetraploid).Conclusions: P. lacustris serves as a first model of the genome structure in Chrysophyceae. Intraspecific variation indicates several mechanisms of diversification including SNPs, change of ploidy and genome reduction. Genetic variation occurs predominantly in non-coding regions or genes belonging to ecological nicheadaptation. The amount of mutations indicates which pathways are more sensitive to mutation and therefore conserved (e.g. energy metabolism) and which are faster evolving (e.g. genetic information processing).