Three clades of Pseudo-nitzschia pungens, determined by the internal transcribed space (ITS) region, are distributed throughout the world. We studied 15 P. pungens clones from various geographical locations and confirmed the existence of the three clades within P. pungens, based on ITS sequencing and described the three subgroups (IIIaa, IIIab, and IIIb) of clade III. Clade III (clade IIIaa) populations were reported for the first time in Korean coastal waters and the East China Sea. In morphometric analysis, we found the ultrastructural differences in the number of fibulae, striae, and poroids that separate the three clades. We carried out physiological tests on nine clones belonging to the three clades growing under various culture conditions. In temperature tests, only clade III clones could not grow at lower temperatures (10°C and 15°C), although clade I and II clones grew well. The estimated optimal growth range of clade I clones was wider than that of clades II and III. Clade II clones were considered to be adapted to lower temperatures and clade III to higher temperatures. In salinity tests, clade II and III clones did not grow well at a salinity of 40. Clade I clones were regarded as euryhaline and clade II and III clones were stenohaline. This supports the hypothesis that P. pungens clades have different ecophysiological characteristics based on their habitats. Our data show that physiological and morphological features are correlated with genetic intraspecific differentiation in P. pungens.
Dolichospermum is a filamentous and heterocytous cyanobacterium that is one of the commonly occurring phytoplanktons in the Han River of Korea. Morphological observations led to the identification of D. planctonicum-like filaments in seasonal water samples. In the present study, we successfully isolated these filaments using culture methods, and examined its morphology using light and scanning electron microscopy. The morphology of the D. planctonicumlike species differed from that of typical D. planctonicum; it had thin cylindrical-shaped akinetes, which were narrower towards the ends than at the center. This morphology is firstly described in the genus Dolichospermum. In addition, the akinetes in the filament developed solitarily and were distant from the heterocytes. Phylogenetic analysis of the 16S rRNA sequences showed that our Dolichospermum clustered with D. planctonicum and D. circinale, which have coiled trichome. However, phylogenetic analysis of the gene encoding rivulose-1,5-bisphosphate carboxylase (rbcLX) clearly separated our species from other Dolichospermum, forming a unique clade. Additionally, structures of D. planctonicum and D. hangangense strains were different type in Box-B and V3 region. These results demonstrated that the new Dolichospermum species was unique in morphology and molecular traits. Therefore, we propose this to be a new species belonging to genus Dolichospermum with the name Dolichospermum hangangense sp. nov.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.