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

Abstract

Wang P., Liang J., Lin X., Chen C., Huang Y., Gao Y. and Gao Y. 2012. Morphology, phylogeny and ITS-2 secondary structure of Pseudo-nitzschia brasiliana (Bacillariophyceae), including Chinese strains. Phycologia 51: 1–10. DOI: 10.2216/09-108.1

The diatom Pseudo-nitzschia brasiliana Lundholm, Hasle & 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.

Key Words::

• Pseudo-nitzschia brasiliana
• Domoic acid
• ITS rDNA
• LSU rDNA
• Secondary structure
• China
• Marine

ACKNOWLEDGEMENTS

This work was supported by the National Natural Science Foundation of China under grant nos. 40831160519, 41076079, 40676080, 40876079, the national 973 project under grant no. 2010CB428704 and the Natural Science Foundation of Fujian Province of China under grant no. 2008J0139. We thank Professor Lu Songhui and Dr. Zhang Yuyu from the Institute of Hydrobiology, Jinan University, for their assistance in sample collection. We are grateful to Professor Nina Lundholm of University of Copenhagen and Professor Yang Li of South China Normal University for their valuable discussions concerning morphology. Dr. Alberto Amato of École Normale Supérieure is thanked for his instructive advice during this work. Professor John Hodgkiss of the University of Hong Kong is thanked for editing the English.