Polyphasic taxonomy of green algae strains isolated from Mediterranean freshwaters

Abstract

BackgroundTerrestrial, freshwater and marine green algae constitute the large and morphologically diverse phylum of Chlorophyta, which gave rise to the core chlorophytes. Chlorophyta are abundant and diverse in freshwater environments where sometimes they form nuisance blooms under eutrophication conditions. The phylogenetic relationships among core chlorophyte clades (Chlorodendrophyceae, Ulvophyceae, Trebouxiophyceae and Chlorophyceae), are of particular interest as it is a species-rich phylum with ecological importance worldwide, but are still poorly understood. In the Mediterranean ecoregion, data on molecular characterization of eukaryotic microalgae strains are limited and current knowledge is based on ecological studies of natural populations. In the present study we report the isolation and characterization of 11 green microalgae strains from Greece contributing more information for the taxonomy of Chlorophyta. The study combined morphological and molecular data.ResultsPhylogenetic analysis based on 18S rRNA, internal transcribed spacer (ITS) region and the large subunit of the ribulose-bisphosphate carboxylase (rbcL) gene revealed eight taxa. Eleven green algae strains were classified in four orders (Sphaeropleales, Chlorellales, Chlamydomonadales and Chaetophorales) and were represented by four genera; one strain was not assigned to any genus. Most strains (six) were classified to the genus Desmodesmus, two strains to genus Chlorella, one to genus Spongiosarcinopsis and one filamentous strain to genus Uronema. One strain is placed in a separate independent branch within the Chlamydomonadales and deserves further research.ConclusionsOur study reports, for the first time, the presence of Uronema in an aquatic environment up to 40 °C and reveals new diversity within the Chlamydomonadales. The results from the ITS region and the rbcL gene corroborated those obtained from 18S rRNA without providing further information or resolving the phylogenetic relationships within certain genera, due to the limited number of ITS and rbcL sequences available. The comparison of molecular and morphological data showed that they were congruent. Cosmopolitan genera with high worldwide distribution inhabit Greek freshwaters.

Novel microalgae strains from selected lower Himalayan aquatic habitats as potential sources of green products

“…Features such as cell shape and arrangement, location of pyrenoid, characteristic spines on the cell surface were all used for the preliminary identification of the strains. Reference was made to microscopic images of strains available in the literature [ 17 – 19 ].…”

DNA barcoding approach to characterize microalgae isolated from freshwater systems in Ecuador

“…They are all found in freshwater systems from different geographic regions, and their sequences match previously published sequences. Scenedesmaceae and Chlorella strains have been found to be the most common aquatic algae isolated from the aquatic systems sampled in our study, as they are the most commonly reported genera of freshwater coccoid green algae with a ubiquitous distribution [33,39]. Some of these species, like Tetradesmus dimorphus, Coelastrella sp., Chlorella vulgaris and C. sorokiniana, have been found throughout the Andean region and present no variability in the barcode sequences.…”

“…The V4 18S rDNA region is considered suitable for molecular analysis due to its greater size and variability of inversions, insertions, and deletions [36,37]. Another promising candidate is the rbcL marker; despite the lack of a universal primer pair for successful rbcL amplification, it is reportedly sufficiently variable to be able to distinguish among most chlorophyte species [18,38,39]. In fact, there are currently c. 9,000 rbcL sequences from chlorophyte species deposited in the DDBJ/EMBL/GenBank database.…”

Optical Insight: Spectrophotometry as a Tool to Quantify Cell Density of Green Microalgae in Suspension, with Emphasis on Growing Conditions and Toxicological Evaluations

“…This behavior is explained by the size of these microorganisms: while the size of Tetraselmis sp. ranges from 10-25 µm long and 7-20 µm wide [39], D. subspicatus has roughly half that size, ranging from 5-13 μm long and 3-7 µm wide [40]. This cell size difference can be visualized in Figures 1b and 1c.…”