Contamination in the model species Cyanidioschyzon merolae NIES-3377

Abstract

Cyanidioschyzon merolae is a thermophilic, unicellular red alga that thrives in acidic hot-spring habitats worldwide. This species possesses simple cell components such as a single plastid, mitochondrion, and Golgi apparatus. The first sequenced eukaryotic algal nuclear genome was that of C. merolae, and the gapless telomere-to-telomere genome subsequently became available. Methods for synchronizing culture and genetic transformations have also been developed. These characteristics indicate that C. merolae is an advantageous experimental resource in molecular cell biology. Specifically, the 10D strain, for which the genome is available, is widely used in many laboratories. However, purification of these strains has received little attention. This study revealed that the NIES-3377 strain, an axenic culture of the 10D strain, was contaminated with another unicellular red alga (Galdieria partita). Furthermore, phylogenetic analysis suggested that the Galdieria strain may not have originated from the same sampling locality as the original 10D strain. The strain was probably contaminated during subculture before being deposited into the culture collection. These results strongly highlight the importance of quality checks for strain establishment and maintenance, particularly in unicellular red algae with similar morphological traits.