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Algae > Volume 24(3); 2009 > Article
Algae 2009;24(3): 129-138. doi: https://doi.org/10.4490/algae.2009.24.3.129
Comparative Molecular Analysis of Freshwater Centric Diatoms with Particular Emphasis on the Nuclear Ribosomal DNA of Stephanodiscus (Bacillariophyceae)
Jang-Seu Ki*
Department of Life Science, College of Natural Sciences, Sangmyung University, Seoul 110-743, Korea
*Corresponding Author  Email: kijs@smu.ac.kr
DNA-based discrimination of species is a powerful way for morphologically otherwise similar species, like centric diatoms. Here, the author sequenced long-range nuclear ribosomal DNAs, spanning from the 18S to the D5 region of the 28S rDNA, of Stephanodiscus, particularly including a Korean isolate. By comparisons, high DNA similarities were detected from the rDNAs of nine Stephanodiscus (>99.4% in 18S rDNA, >98.0% in 28S rDNA). Their genetic distances, however, were significantly different (Kruskal-Wallis test, p < 0.01) compared to two related genera, namely Cyclotella and Discostella. In addition, genetic distances of 18S rDNAs were significantly different (Student’s t-test, p = 0.000) against those of the 28S rDNAs according to individual genera (Cyclotella, Discostella, and Stephanodiscus). Phylogenetic analyses showed that Stephanodiscus and Discostella showed a sister taxon relationship, and their clade was separated from a cluster of Cyclotella (1.00 PP, 100% BP). This suggests that Stephanodiscus has highly conserved sequences of both 18S and 28S rDNA; however, Stephanodiscus is well-separated from other freshwater centric diatoms, such as Cyclotella and Discostella, at the generic level.
Key words: freshwater diatom, nucleotide divergence, phylogeny, ribosomal DNA, Stephanodiscus

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