Desmodesmus pseudoperforatus sp. nov., a giant in Desmodesmus, series Maximi

• Published in: European journal of phycology Vol. 59; no. 3; pp. 254 - 270
• Main Authors: Hegedűs, Adriana, Porav, Alin Sebastian, Tripon, Septimiu Cassian, Dragoș, Nicolae
• Format: Journal Article
• Language: English
• Published: Cambridge Taylor & Francis 02.07.2024; Taylor & Francis Ltd
• Subjects: Candidate species; Cell morphology; Cell walls; Deoxyribonucleic acid; Desmodesmus; Desmodesmus pseudoperforatus; DNA; DNA sequences; DNA structure; Freshwater; Freshwater environments; Inland water environment; ITS2; Light microscopy; microperforations; Morphology; New species; Nucleotide sequence; Phylogenetics; Phylogeny; Protein structure; Secondary structure; series Maximi; species boundaries; SSU rDNA; Ultrastructure
• ISSN: 0967-0262; 1469-4433
• DOI: 10.1080/09670262.2024.2338510

Series Maximi is a group within Desmodesmus (Chlorophyta) which contains the three species D. maximus, D. perforatus and D. tropicus. Besides their large cell sizes, the most striking morphological trait unique to the members of this genus is the presence of large perforations between the coenobial cells. The perforations are either present (D. perforatus and D. tropicus) or the space between the cells is completely sealed (D. maximus). We report here a fourth species of the series based on two strains (AICB 1155 and AICB 1572) from freshwater environments of the Danube Delta, Romania. The ultrastructure of the cell walls revealed a partial closure of the space between the cells which creates slightly visible perforations in light microscopy. Analyses of DNA sequences and secondary structure of the ITS2 fragment by coalescent (PTP, GMYC), distance (ASAP), and evolutionary modelbased methods (ML, BI) indicated a fourth candidate species which included both the AICB strains investigated and other strains with similar morphological traits from reference literature. Despite its poor representation in public databases, analysis of the SSU rDNA gene for the series Maximi strengthened the ITS2 results. Therefore, based on its larger cell sizes relative to the other members of the series, cell morphology, the presence of partial perforations and other peculiarities of the cell wall ultrastructure, the independent phylogenetic position, CBCs analysis, and a different 'DNA signature' within the ITS2 fragment we suggest that this clade should be described as a new taxon of the series Maximi, Desmodesmus pseudoperforatus sp. nov. Morphological differences and DNA-based lines of evidence indicate new species. Microperforations of the space between the coenobial cells. Strains have the largest cell sizes in the series Maximi.