LAUSR

Green microalgae are of the utmost importance to aquatic ecosystems globally, as they are primary producers and major food sources for many organisms. Microalgae of the genus Choricystis are common in Lake Baikal, yet genetic diversity and phylogenetic relationships of the genus are not well known. Nuclear 18S rRNA, plastid rbcL and 16S rRNA gene sequences from open databases were used to investigate the relationships within the genus Choricystis and to specify the phylogeny and diversity of these microalgae in Lake Baikal. Sequences derived from both planktonic Choricystis and endosymbiotic Choricystis living within Baikal endemic sponges were analysed. Species delimitation was performed using bioinformatic methods. Analysis of the three genetic markers showed two major phylogenetic lineages in the genus Choricystis, with the highest genetic diversity observed in the rbcL gene analysis. Two different phylogenetic clusters included sequences of strains with the same species name, Choricystis parasitica (K. Brandt) Pröschold & Darienko, raising the question of hidden diversity within this species. Choricystis algae in Lake Baikal are represented by three genetic variants, two of which are distinct from Choricystis parasitica. Analysis of nuclear and plastid genes in microalgae of the genus Choricystis showed higher genetic diversity than previously thought and a possible endemic speciation in Lake Baikal.