The freshwater green algal genus Desmodesmus contains many cryptic species that are difficult to identify using morpho-anatomy. This study analyzed 310 ITS2 sequences related to Desmodesmus species from GenBank and developed a new tool named DNA signaturing. DNA signaturing is a species identification method using signature sequences specific for each species or strain group within the genus Desmodesmus. These signature sequences had 18-33 nucleotides in length. This tool could exactly identify 19 species and 24 strain groups of Desmodesmus. In addition, a signature sequence, AGA GGC TTA AAC TGG GAC C, was specific for almost 90% of Desmodesmus strains and could represent the genus Desmodesmus. A strain MLC1 isolated from freshwater in Da Nang, Vietnam, was identified as Desmodesus pseudoserratus by this tool. DNA signaturing tool described here showed the highest efficacy for identifying strains and a remarkable ability to accurately classify cryptic species in the genus Desmodesmus.
Species identification of Scenedesmus‐like microalgae, comprising Desmodesmus, Tetradesmus, and Scenedesmus, has been challenging due to their high morphological and genetic similarity. After developing a DNA signaturing tool for Desmodesmus identification, we built a DNA signaturing database for Tetradesmus. The DNA signaturing tool contained species‐specific nucleotide sequences of Tetradesmus species or strain groups with high similarity in ITS2 sequences. To construct DNA signaturing, we collected data on ITS2 sequences, aligned the sequences, organized the data by ITS2 sequence homology, and determined signature sequences according to hemi‐compensatory base changes (hCBC)/CBC data from previous studies. Four Tetradesmus species and 11 strain groups had DNA signatures. The signature sequence of the genus Tetradesmus, TTA GAG GCT TAA GCA AGG ACCC, recognized 86% (157/183) of the collected Tetradesmus strains. Phylogenetic analysis of Scenedesmus‐like species revealed that the Tetradesmus species were monophyletic and closely related to each other based on branch lengths. Desmodesmus was suggested to split into two subgenera due to their genetic and morphological distinction. Scenedesmus must be analyzed along with other genera of the Scenedesmaceae family to determine their genetic relationships. Importantly, DNA signaturing was integrated into a database for identifying Scenedesmus‐like species through BLAST.
The new species can be easily distinguished from all other Protosticta species by the combination of huge body size, birdhead shape of cerci and paraprocts broad and apically armed with several sharp subapical projections in the male, and the anterior pronotal lobe of the prothorax well developed in the female.
Haematococcus lacustris is capable to synthesize high content of astaxanthin. Moreover, astaxanthin extracted from H.lacustris has been shown to have the highest anti-oxidativeactivity. While the demand for astaxanthin in the world is increasing, the production of astaxanthin from H. lacustris is still not easy since they have low growth rate and are very sensitive to changes in culture conditions. This study aimed at investigating the effect of nutritional factors on the growth rate of H. lacustris in order to determine the optimal medium for the biomass growth and astaxanthin synthesis of this specy. The results showed that H.lacustris grew better in RM culture medium (2.62 ± 0.17 × 10 5 cells/ml) than in BBM culture medium (2.44 ± 0.10 × 10 5 cells/ml). The highest cell density of H. lacustris was achieved in the RM medium with NaNO3 at 1200 mg/l (3.72 ± 0.022 × 10 5 cells/ml), and in the RM medium with K2HPO4 at 320 mg/l (3.42 ± 0.05 × 10 5 cells/ml).
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