Morphology, phylogeny and ITS-2 secondary structure of Pseudo-nitzschia brasiliana (Bacillariophyceae), including Chinese strains

The diatom Pseudo-nitzschia brasiliana Lundholm, Haste & G.A. Fryxell is documented from China for the first time. Strains isolated from southeast coastal waters were characterized using light and. electron microscopic observation. All strains were tested for domoic acid, but no toxin was detected. Genetic diversity and phylogenetic relationships of global strains of P. brasiliana were studied to assess intraspecific variation and geographic distribution patterns. Phylogenetic analyses based on the large subunit rDNA gene together with morphological observations show that P. brasiliana from China and other locations worldwide form one well-supported monophyletic clade, with P. americana as its sister. Phylogenetic analyses of internal transcribed spacer (ITS) rDNA sequences show a clear separation between five Asian strains and three European strains. In addition, ITS-2 rDNA secondary structure analyses reveal genetic variation between P. brasiliana strains from Europe and Southeast Asia, namely, a transfer of a base-pair set from a loop in the Asian group to the basis of helix II in the European group and two hemi-compensatory base changes (hemi-CBCs) in helix III between one European strain (ICMB-176) and the other strains. The occurrence of P. brasiliana in China's coastal waters is discussed.