|Other Abstract||To date, more than 100 taxa of genus Anabaena including about 40 planktonic have been reported in the world. However, there are few researches of planktonic Anabaena in China, and only several species were described in China so far. Information about molecular phylogenetic studies based on Chinese planktonic Anabaena strains is quite limited. The phylogenetic relationships of planktonic Anabaena with benthic Anabaena, Aphanizomenon, Anabaenopsis, Trichormus, Nostoc and Nodularia are not clear.
In this study, 175 strains of planctonic Anabaena have been obtained by our wide range of sample collection. Through morphological observation such as the shape of trichomes, the characters and dimensions of vegetative cells, heterocysts and akinetes, the position of heterocysts and akinetes, these planktonic Anabaena strains can be identified into eleven species. Among them, eight species are new record to China, and they are Anabaena affinis Lemmermann 1897, Anabaena planctonica Brunnthaler 1903, Anabaena kisseleviana Elenkin 1938, Anabaena aphanizomenioides Forti 1912, Anabaena bergii Ostenfeld 1908, Anabaena ucrainica (Schkorb.) Watanabe 1996, Anabaena oumiana Watanabe 1996 and Anabaena eucompacta Li et Watanabe 1999. The other three species are common in Chian, they are Anabaena spiroides Kleb. 1895, Anabaena circinalis Rab. 1852 and Anabaena flos-aquae （Lyngb.）Breb., 1836.
Three gene 16S rDNA、PC-IGS and rbcLX have been analyzed, and phylogenetic trees based on sequences of these three genes were constructed using NJ and ML methods. Results showed that the phylogenetic relationships of planktonic Anabaena with Trichormus, Nostoc Anabaenopsis, Nodularia and Cyanospira are further than those of planctonic Anabaena with benthic Anabaena, Aphanizomenon and Cylindrospermopsis. Many planktonic Anabaena species in this study were not shown to have genetic differences or differentiate geographically. Among the three genes, the evolutionary speed of rbcLX gene is relatively faster, and it is thus more adaptive to use rbcLX gene sequence for analyzing the molecular phylogenetic relationship between planktonic Anabaena with other genera of Nostocaceae.
Strains of Anabaena ucrainica were shown to produce taste & odor substance --geosmin, with high amounts (between 1.09×10-5 to 2.60×10-5ng•cell-1), based on laboratory culture of these strains at the log phase. The ability in producing geosmin of these different Anabaena ucrainica strains are extremely different, and main reasons may be the combined genetic and environmental factors. Comparing the partial sequence of geosmin synthase gene examined in strains of Anabaena ucrainica with that of Nostoc punctiforme PCC 73102 and Phormidium sp., it is suggested that the geosmin synthase gene of cyanobateria was faster in evolutionary speed.|