Diversity in Cyanidiophyceae: Cyanidiofrigus pintoensis gen. et sp. nov. within polyextremophilic red algae (Rhodophyta)

ABSTRACT

The polyextremophilic red algal class Cyanidiophyceae inhabits a wide range of extreme habitats (e.g. acidic geothermal areas and dim-light caves), and shows various cell morphologies (e.g., subspherical and club-shape) and trophic strategies (e.g., photoautotrophy, heterotrophy and mixotrophy). Historically, inconsistent observations of morphology and physiology have hindered taxonomic advancements in Cyanidiophyceae despite indications of species diversity from molecular studies. Here we revisited this taxonomic conundrum and explored their cryptic speciation based on multi-locus and morpho-physiological evidence examined from expanded taxa sampling, including 20 cultures and one environmental sample. Our multi-locus phylogeny revealed two well-supported monophyletic lineages: the C-lineage that is generically rich (including Cavernulicola, Cyanidiococcus, Cyanidiofrigus, Cyanidioschyzon, Cyanidium, Gronococcus, and Sciadococcus) and the G-lineage that currently only contains the genus Galdieria. Species delimitation analyses revealed at least 21 species in Cyanidiophyceae. Although our morpho-physiological observations failed to differentiate closely related species apart within a genus, we propose Cyanidiofrigus pintoensis gen. et sp. nov. as this species is in a highly divergent lineage with much lower thermal tolerance than other recognized species. Overall, our study fills the taxonomic knowledge gaps and expands the number of known species in Cyanidiophyceae.

KEYWORDS:

• Algorithmic Species Delimitation
• Morpho-physiological Investigation
• Multi-locus Phylogeny

ACKNOWLEDGEMENTS

We extend our sincere gratitude to Robert A. Andersen (Friday Harbor Laboratories, University of Washington, Friday Harbor, USA) for his invaluable guidance and advice on the nomenclatural issue, which greatly contributed to the clarity and accuracy of our study. We also express our appreciation to Dr. Wann-Neng Jane (the Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan) for his exceptional contributions in TEM sample preparation and picture acquisition. Furthermore, we would like to acknowledge Miss Yu-Ti Huang for her invaluable assistance in conducting meticulous morphological observations that significantly enriched our research.

DISCLOSURE STATEMENT

No potential conflicts of interest are reported by the authors(s).

Supplemental data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00318884.2024.2324424

Additional information

Funding

This work was supported by grants from the Ministry of Science and Technology, Taiwan to SLL (MOST105-2628-B-029-001-MY3), the National Science and Technology Council, Taiwan (NSTC111-2621-B-029 -002-MY3) and the National Research Foundation of Korea (NRF-2022R1A2B5B03002312) to HSY.