Molecular characterizations of Thai Raphidiopsis raciborskii (Nostocales, Cyanobacteria) based on 16S rDNA, rbcLX, and cylindrospermopsin synthetase genes

抄録

Raphidiopsis (previously Cylindrospermopsis) raciborskii is considered as a cylindrospermopsin (CYN) producer in Thailand. There are no reports including molecular information on the genes associated with CYN production of cyanobacteria from Thailand. In the present study, 27 new R. raciborskii strains from Thailand were isolated. Their morphological features and phylogenetic positions based on the partial sequences of 16S rDNA and rbcLX were analyzed for identification. Morphological characteristics of all the strains tested, and the natural samples, were found to be similar to the original description of R. raciborskii. The rbcLX phylogenetic trees revealed that the clade of R. raciborskii is independent from those of R. mediterranea and R. curvata, whereas the 16S rDNA phylogenetic trees failed to discriminate these species. Thus, all the strains tested in the present study were identified as R. raciborskii. Furthermore, the LC/MS/MS analysis confirmed that some of the strains tested produced CYN and 7-deoxy-CYN. The presence of genes associated with CYN biosynthesis (cyrA, cyrB, cyrC, and cyrJ) in Thai Raphidiopsis strains was investigated by PCR and phylogenetic analyses. Results of PCR showed that the PCR amplicons of cyrB and cyrJ were obtained from all toxic strains, while the amplicons of cyrA and cyrC were not obtained in some toxic Thai strains. Our findings supported the observation that cyrB and cyrJ, especially the latter, may be useful for the detection of CYN-producing cyanobacteria in water resources for water supplies and fisheries.