Emendation of Rhodomonas marina (Cryptophyceae):insights from morphology, molecular phylogeny and water-soluble pigment in an Arctic isolate.

• Published in: Algae
• Main Authors: Daugbjerg, Niels, Devantier, Cecilie B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2024
• Subjects: Arctic; Greenland; Gullet
• Online Access: https://curis.ku.dk/portal/da/publications/emendation-of-rhodomonas-marina-cryptophyceae(eb4732b0-bf55-4b11-a853-7bf8364873c6).html; https://doi.org/10.4490/algae.2024.39.6.13; https://curis.ku.dk/ws/files/395388663/algae_2024_39_6_13.pdf

Rhodomonas (Cryptophyceae) and species assigned to this genus have undergone numerous taxonomic revisions. This also applies to R. marina studied here as it was originally assigned as a species of Cryptomonas and later considered a variation of R. baltica, the type species. Despite being described more than 130 years ago, R. marina still lacks a comprehensive characterization. Light and electron microscopy were employed to delineate a strain from western Greenland. The living cells were 18 μm long and 9 μm wide, elliptical in shape with a pointed to rounded posterior and truncated anterior in lateral view. Two sub-equal flagella emerged from a vestibulum, where also a furrow extended. In transmission electron microscopy, the furrow was associated with a tubular gullet and the pyrenoid embedded in a deeply lobed chloroplast. The chloroplast contained DNA in perforations and was surrounded by starch grains. A tubular nucleomorph was enclosed within the pyrenoid matrix. In scanning electron microscopy, the inner periplast consisted of rectangular plates with rounded edges and posteriorly these were replaced by a sheet-like structure. The water-soluble pigment was Crypto-Phycoerythrin type I (Cr-PE 545). A phylogenetic inference based on SSU rDNA confirmed the identity of strain S18 as a species of Rhodomonas as it clustered with congeners but also Rhinomonas, Storeatula, and Pyrenomonas. These genera formed a monophyletic clade separated from a diverse assemblage of other cryptophyte genera. To further explore the phylogeny of R. marina a concatenated phylogenetic analysis based on the SSU rDNA-ITS1-5.8S rDNA-ITS2- LSU rDNA region was performed but included only closely related species. The secondary structure of nuclear internal transcribed spacer 2 was predicted and compared to similar structures in related species. Using morphological and molecular signatures as diagnostic features the description of R. marina was emended.