First isolation report and molecular phylogenetic characteristics of Raphidiopsis raciborskii in South Korea

As a result of global warming, aquatic ecosystems undergo changes such as the increase in the occurrence of harmful algal bloom and the introduction of new alien species. Raphidiopsis raciborskii originated in the tropical eutrophic system, but now it has expanded to the temperate zone according to climate change and has been found in many areas, including China and Japan. This cyanobacterium is a kind of harmful algae that is likely to produce toxins and has never been isolated in Korea. In this study, molecular genetic analysis was performed using cpcBA-IGS, nifH, and 16S rRNA gene that can estimate geographical relationships as well as microscopic observation of R. raciborskii isolated from a reservoir in Incheon for the first time in South Korea. The isolate was characterized by heterocyst that was responsible for nitrogen fixation at the ends of straight trichome. It was identified as R. raciborskii according to the morphology of the apical cell and akinete. Molecular genetic analysis of cpcBA-IGS and nifH showed that there is a closer relationship with the strains isolated in Asia, Europe, Australia, and Africa. R. raciborskii is highly likely to be distributed nationwide because straight, and S-shaped individuals were also observed in reservoirs in Incheon, Uiwang, and Hwaseong. In addition, since strains that produce toxins are found in Asia, and Australia, it is necessary to study their ecological characteristics along with nationwide distribution survey.