Morphological and phylogenetic analysis of a non-toxic Raphidiopsis curvispora isolated from a drinking water reservoir in South Korea

Tropical and subtropical cyanobacteria have been increasingly reported in temperate regions. The genus Raphidiopsis is rarely observed in South Korea. To date, R. curvispora has been reported generally in tropical and subtropical regions, such as Africa and South-east Asia. R. curvispora strain GIHE-G1 was isolated in a drinking water reservoir in South Korea for the first time in July 2020, and its whole genome was sequenced. The complete genome sequence indicated that the strain did not contain any cyanotoxin genes. Morphologically, the GIHE-G1 strain is more similar to the African than Japanese strain, which has a closer geographical distribution. Phylogenetic analysis of several genetic markers, such as 16S rRNA, phycocyanin intergenic spacer (cpcBA-IGS), nitrogenase gene (nifH) and RNA polymerase gene (rpoC1), did not show geographical characteristics or a close relationship with the African strains, unlike the case of Raphidiopsis raciborskii. Moreover, a minimal genetic relationship with Raphidiopsis from China was found. Considering the morphological and genetic characteristics, R. curvispora strain GIHE-G1 was likely introduced a long time ago or is native to Korea and is becoming more noticeable because of recent environmental changes.