Genetic Structure, Phylogeography Relationship And PSP Toxin Profile Of Alexandrium Tamarense Species Complex

The Alexandrium tamarense species complex is one of the most important marine dinoflagellates in term of the severity, diversity, and distribution of bloom impacts. Most of this species are known to be toxic or have otherwise harmful effect. A. tamarense is widely distributed along the coast of China, and often forms large algal blooms in the water surrounding of the Bohai Sea, Zhoushan and Xiamen in China. However, its genetic diversity, genetic differentiation level, genetic relationship with strains from other waters and the PSP toxin characteristic remain obscure.Here, the genetic diversity and evolutionary relationship of A. tamarens were investigated using AFLP. Total 82 strains of this species isolated from different geographic locations were tested, and 370 polymorphic sites were found. Nei’s gene diversity ranged from 0.137 to 0.266 with an average of 0.186, while Shannon index ranged from 0.190 to 0.408 with an average of 0.275. Different genetic differentiation coefficient(Fst) were observed between populations, ranging from 0.007 to 0.303. The lowest Fst value was found between population from the East of China Sea and the North China sea, followed by that from the Chukchi Sea, and the Yellow Sea and the Bohai Sea. The gene flow beween populations(Nm) was 1.628. The principal coordinates analysis(PCo A) and STRUCTURE analysis revealed that 82 isolates of A. tamarense could be divided into four groups. Strains from the Bohai Sea, the Yellow Sea and the Chukchi Sea were clustered into one group. Taking into account of all these results, we proposed that the strains from the Bohai Sea, the Yellow Sea and the Chukchi Sea might be descended from the same parental stock.The PSP toxin profiles in 60 strains of A. tamarense were analyzed. However, no PSP toxins were detected in 11 strains of A. tamarense. The PSP toxins identified include the carbamate toxins STX, neosaxitoxin(NEO), GTX-1/4 and GTX-2/3, and the less toxic N-sulfocarbamoyl toxins C1/2 and B1, and decarbamoyl toxins dc GTX2/3 and dc STX. Among the 47 Chinese strains, 45 strains of A. tamaranse were shown to produce PSP toxins. The toxins with the highest concentration in the profile were C1/2, GTX1/4 and NEO. The mean toxin concentration was 6.65 fmol/cell(n=45), with a maximum of 31.33 fmol/cell(in ATDH05) and a minimum 0.02 fmol/cell(in ATDH26). The mean specific toxicity among strains was 1.04 pg STXeq/cell(n=45) with the highest value of 7.88 pg STXeq/cell and the lowest of 0.001 pg STXeq/cell. No strict correlation was observed between the PSP toxins profile and the geographical distribution.