Molecular Phylogeny Analysis Of The Main Bait-Microalgae

Some bait-microalgaes were selected from MACC, including Chlorophyta(Dunaliella, Tetraselmis, Chlorella), Chrysophyta(Isochrysis, Pavlova), Bacillariophyta(Nitzschia, Phaeodactylum, Chaetoceros). Their taxonomic position were undefined. To provide molecular basis for the relationship and identification, the18SrRNA and ITSrRNA sequences were amplified and sequenced, phylogenetic relationship among these sequences and some other related algae sequences from GenBank were also analyzed.The analysis results of 1671-1729bp 18SrRNA sequences in Chlorophyta showed that: (1) The GC content of 26 Dunaliella strains ranged from 48.4% to 49.0%. There are 1531 conserve loci, 92 transition and transversion loci, 15 insert or deletion loci in total of 1638 loci. The mutation rate of transition and transversion is 5.6%, while the mutation rate of insert or deletion is 0.9%. Analysis results of phylogenetic relationship implied that 26 strains of Dunaliella can be divided into three clads: D.salina, D.bardawil, D.tertiolecta, D.bioculata, D.primolecta and D.parva clustered in one clad, D.viridis and D.lateralis strain Nepal clustered into two clad separately. The result was consistent with ITS1 and ITS2. According to the sequence diversity, seven Dunaliella sp. A43, A57, A83, A85, C43 had closely affinity with D.viridis, could be identified as different strains of D.viridis. A121 and A124 stood between D.salina and D.viridis according to 18SrRNA sequence, and became closer to D.viridis according to ITSrRNA sequence. (2) The GC content of 19 Tetraselmis strains ranged from 46.8% to 47.7%, There are 1551 conserve loci, 66 transition and transversion loci, 11 insert or deletion loci in total of 1628 loci. The mutation rate of transition and transversion is 4.1%, while the mutation rate of insert or deletion is 0.7%. Analysis results of phylogenetic relationship showed that 26 strains of Tetraselmis can be divided into 4 clads, C75 had closely affinity with T.striata, C73, C74, C152 were much closer to T.suecica strain KMMCC P-9 and T.subcordiformis; C151 could belong to T. helgolandica var.tsingtaoensis. (3) The highest GC content of Chlorella 18SrRNA sequences is close to 50%. There are 1707 conserve loci, 49 transition and transversion loci, 0 insert or deletion loci in total of 1756 loci. The mutation rate of transition and transversion was 2.8%, while the mutation rate of insert or deletion was 0. Strain CF126 was most closely related to C.sorokiniana.The analysis results of two Chrysophyta genus showed that: (1) 18SrRNA sequence of 23 strains of Pavlova, There are 1464 conserve loci, 180 transition and transversion loci, 70 insert or deletion loci in total of 1714 loci. The phylogenetic relationship analysis showed that 23 strains of Pavlova can be divided into four clades, 8 strains of Pa.pinguis and 1 strain of Pa.pseudogranifera clustered firstly in a clade, 5 strains of Pa.gyrans clustered in one clade, 3 strains of Pa. salina clustered in one clade, BF of MACC and a strain of Pa.viridis clustered firstly, then clustered further in one clade with Pa.virecens and Pa.lutheri. (2) Match results of 7 Isochrysis strains showed that 1399 sites were compared, the number of conserve sites are 1341, the number of transition and transversion sites are 45, the number of insert or deletion sites are 13. Analysis results of phylogenetic relationship show that 3011, 8701 and Isochrysis galbana (I. galbana) had a very close affinity, S18, S29 were closer to I. aff. Galbana 'Tahitian isolate'.The18SrRNA sequence length of 4 Diatom strains were 1687-1726bp. Phylogenetic relationship among these sequences and 22 related algae sequences from GenBank were compared. The results implied that all the strains of Nitzschia, Phaeodactylum, Chaetoceros can be devided through 18S rRNA. B253, B228 and P.triconutum clustered in one clade, which suggested B253, B228 were different strains of P.triconutum, B13 and C.gracilis clustered in one clade. The result also indicated that it was Nitzschia closterium f.minutissima which clustered in one clade with P.triconutum entirely, not N.closterium. Nitzschia closterium f.minutissima had a closer affinity with P.triconutum.