Nitzschia closterium f. minutissima, a marine eukaryotic unicellular diatom, originally classified as Bacillariophyta/Bacillariophyceae/Bacillariales/Bacillariaceae/Nitzschia, is one of the most important feed sources in mariculture. In this study, its morphological features were examined under DIC Microscopy (differential interference contrast microscope); its pigments and fatty acids composition were analyzed by using High Performance Liquid Chromatography (HPLC) and gas chromatography (GC); the complete Actin cDNA, part 18S rDNA, complete ITS1 and ITS2 sequences, part 28S rDNA se- quences, and a putatively encoding ?5 fatty acid desaturase gene were cloned respectively and further functioned in transgenic yeast. The sequence alignments were separately conducted using the related sequences from Nitzschia closterium f. minutissima, Cylindrotheca closterium (Bacillariophyta/Baci- llariales/Bacillariaceae/Cylindrotheca) and Phaeodactylum tricornutum (Naviculales) with ClustalX 1.83. No distinct difference was discovered between N. closterium f. minutissima and P. tricornutum in both biochemical and molecular level. Their identity was more than 99.6% among 18S rDNA, 5.8S rDNA and actin-gene sequences, and is up to 98.6% even among ITS1 and ITS2 sequences. Their ?5 desaturase similarity was 99.4%. However, the lower similarity was disclosured between N. closterium f. minutis- sima and Cylindrotheca closterium, which shared less than 40% identity in the ITS1 and ITS2 se- quences. So, N. closterium f. minutissima should not be placed in Bacillariales, Bacillariaceae, Nitzschia, but in Naviculales, Phaeodactylaceae, Phaeodactylum, and it was actually a strain of P. tri- cornutum.
SHI JuanPAN KeHouWANG XiaoQingCHEN FangZHOU MiZHU BaoHuaQING RenWei
Prorocentrum donghaiense has caused large-scale red tides off the Chinese coast in recent years. Expressed sequence tag （EST） analysis was carried out for this dinoflagellate in order to identify the functional genes involved in its biological processes. A cDNA library was constructed for P. donghaiense at exponential growth phase, and 565 usable sequencing reads were obtained from 700 clones selected randomly. Messenger RNA corresponding reads were clustered into 36 contigs and 272 singletons （EST groups）. Twenty-two EST groups were found to tag the genes involved in diverse biological processes including programmed cell death （PCD）. Two EST groups showed significant homologies with the encoding genes of cysteine protease （caspase） and proliferating cell nuclear antigen, respectively, two key proteins involved in PCD.
