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DNA-Based Taxonomy in Ecologically Versatile Microalgae: A Re-Evaluation of the Species Concept within the Coccoid Green Algal Genus Coccomyxa (Trebouxiophyceae, Chlorophyta).

Malavasi V, Škaloud P, Rindi F, Tempesta S, Paoletti M, Pasqualetti M - PLoS ONE (2016)

Bottom Line: Our results are compared with those of a recent integrative study of Darienko and colleagues that reassessed the taxonomy of Coccomyxa, recognizing 7 species in the genus.We conclude that the 27-species scenario is presently the most realistic for Coccomyxa and we suggest that well-supported lineages distinguishable by ecological preferences should be recognized as different species in this genus.We also recommend that for microbial lineages in which the overall diversity is unknown and taxon sampling is sparse, as is often the case for green microalgae, the results of analyses for algorithmic DNA-based species delimitation should be interpreted with extreme caution.

View Article: PubMed Central - PubMed

Affiliation: Interdepartmental Center of Environmental Science and Engineering (CINSA), University of Cagliari, Cagliari, Italy.

ABSTRACT
Coccomyxa is a genus of unicellular green algae of the class Trebouxiophyceae, well known for its cosmopolitan distribution and great ecological amplitude. The taxonomy of this genus has long been problematic, due to reliance on badly-defined and environmentally variable morphological characters. In this study, based on the discovery of a new species from an extreme habitat, we reassess species circumscription in Coccomyxa, a unicellular genus of the class Trebouxiophyceae, using a combination of ecological and DNA sequence data (analyzed with three different methods of algorithmic species delineation). Our results are compared with those of a recent integrative study of Darienko and colleagues that reassessed the taxonomy of Coccomyxa, recognizing 7 species in the genus. Expanding the dataset from 43 to 61 sequences (SSU + ITS rDNA) resulted in a different delimitation, supporting the recognition of a higher number of species (24 to 27 depending on the analysis used, with the 27-species scenario receiving the strongest support). Among these, C. melkonianii sp. nov. is described from material isolated from a river highly polluted by heavy metals (Rio Irvi, Sardinia, Italy). Analyses performed on ecological characters detected a significant phylogenetic signal in six different characters. We conclude that the 27-species scenario is presently the most realistic for Coccomyxa and we suggest that well-supported lineages distinguishable by ecological preferences should be recognized as different species in this genus. We also recommend that for microbial lineages in which the overall diversity is unknown and taxon sampling is sparse, as is often the case for green microalgae, the results of analyses for algorithmic DNA-based species delimitation should be interpreted with extreme caution.

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Morphology of Coccomyxa melkonianii SCCA048.A-D. Morphological plasticity of vegetative cells, E-F. Cells containing two plastids, G. Accumulation of lipid droplets in the cytoplasm, H-I. Formation of small mucilaginous caps, J. Mature cells (note the autospore formation at the bottom left cell). Scale bars = 5 μm.
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pone.0151137.g002: Morphology of Coccomyxa melkonianii SCCA048.A-D. Morphological plasticity of vegetative cells, E-F. Cells containing two plastids, G. Accumulation of lipid droplets in the cytoplasm, H-I. Formation of small mucilaginous caps, J. Mature cells (note the autospore formation at the bottom left cell). Scale bars = 5 μm.

Mentions: Cells of the strain Coccomyxa sp. SCCA048 were morphologically highly variable (Fig 2), exhibiting elongated cylindrical (Fig 2A), ovoid (Fig 2B), broadly ellipsoidal (Fig 2C), and drop-like shapes (Fig 2D). They usually contained a single parietal chloroplast (Fig 2B and 2D), though two chloroplasts were rarely observed (Fig 2E and 2F). Mature cells were often filled by lipid droplets of various size (Fig 2G). Mucilaginous colonies were never formed, although cultivated in either liquid or agar-solidified media. Small mucilaginous caps were, however, observed in a few cells (Fig 2H and 2I). Asexual reproduction took place by cell division and a formation of 2–4 autospores (Fig 2J), released by rupture of the cell wall at the rounded apex of the cell.


DNA-Based Taxonomy in Ecologically Versatile Microalgae: A Re-Evaluation of the Species Concept within the Coccoid Green Algal Genus Coccomyxa (Trebouxiophyceae, Chlorophyta).

Malavasi V, Škaloud P, Rindi F, Tempesta S, Paoletti M, Pasqualetti M - PLoS ONE (2016)

Morphology of Coccomyxa melkonianii SCCA048.A-D. Morphological plasticity of vegetative cells, E-F. Cells containing two plastids, G. Accumulation of lipid droplets in the cytoplasm, H-I. Formation of small mucilaginous caps, J. Mature cells (note the autospore formation at the bottom left cell). Scale bars = 5 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814044&req=5

pone.0151137.g002: Morphology of Coccomyxa melkonianii SCCA048.A-D. Morphological plasticity of vegetative cells, E-F. Cells containing two plastids, G. Accumulation of lipid droplets in the cytoplasm, H-I. Formation of small mucilaginous caps, J. Mature cells (note the autospore formation at the bottom left cell). Scale bars = 5 μm.
Mentions: Cells of the strain Coccomyxa sp. SCCA048 were morphologically highly variable (Fig 2), exhibiting elongated cylindrical (Fig 2A), ovoid (Fig 2B), broadly ellipsoidal (Fig 2C), and drop-like shapes (Fig 2D). They usually contained a single parietal chloroplast (Fig 2B and 2D), though two chloroplasts were rarely observed (Fig 2E and 2F). Mature cells were often filled by lipid droplets of various size (Fig 2G). Mucilaginous colonies were never formed, although cultivated in either liquid or agar-solidified media. Small mucilaginous caps were, however, observed in a few cells (Fig 2H and 2I). Asexual reproduction took place by cell division and a formation of 2–4 autospores (Fig 2J), released by rupture of the cell wall at the rounded apex of the cell.

Bottom Line: Our results are compared with those of a recent integrative study of Darienko and colleagues that reassessed the taxonomy of Coccomyxa, recognizing 7 species in the genus.We conclude that the 27-species scenario is presently the most realistic for Coccomyxa and we suggest that well-supported lineages distinguishable by ecological preferences should be recognized as different species in this genus.We also recommend that for microbial lineages in which the overall diversity is unknown and taxon sampling is sparse, as is often the case for green microalgae, the results of analyses for algorithmic DNA-based species delimitation should be interpreted with extreme caution.

View Article: PubMed Central - PubMed

Affiliation: Interdepartmental Center of Environmental Science and Engineering (CINSA), University of Cagliari, Cagliari, Italy.

ABSTRACT
Coccomyxa is a genus of unicellular green algae of the class Trebouxiophyceae, well known for its cosmopolitan distribution and great ecological amplitude. The taxonomy of this genus has long been problematic, due to reliance on badly-defined and environmentally variable morphological characters. In this study, based on the discovery of a new species from an extreme habitat, we reassess species circumscription in Coccomyxa, a unicellular genus of the class Trebouxiophyceae, using a combination of ecological and DNA sequence data (analyzed with three different methods of algorithmic species delineation). Our results are compared with those of a recent integrative study of Darienko and colleagues that reassessed the taxonomy of Coccomyxa, recognizing 7 species in the genus. Expanding the dataset from 43 to 61 sequences (SSU + ITS rDNA) resulted in a different delimitation, supporting the recognition of a higher number of species (24 to 27 depending on the analysis used, with the 27-species scenario receiving the strongest support). Among these, C. melkonianii sp. nov. is described from material isolated from a river highly polluted by heavy metals (Rio Irvi, Sardinia, Italy). Analyses performed on ecological characters detected a significant phylogenetic signal in six different characters. We conclude that the 27-species scenario is presently the most realistic for Coccomyxa and we suggest that well-supported lineages distinguishable by ecological preferences should be recognized as different species in this genus. We also recommend that for microbial lineages in which the overall diversity is unknown and taxon sampling is sparse, as is often the case for green microalgae, the results of analyses for algorithmic DNA-based species delimitation should be interpreted with extreme caution.

Show MeSH
Related in: MedlinePlus