The Studies On Cylindrotheca Closterium Species Complex And Diversity Analysis Of The Genus Thalassiosira

The genus Cylindrotheca is a small group of marine diatoms with a few species described. Cylindrotheca closterium (Ehrenberg) Lewin et Reimann (= Nitzschia closterium) can be collected in Jiaozhou Bay all year around, which is commonly used for bivalve rearing. Identification of C. closterium may have caused more problems and more confusion than the identification of any other diatom encountered in marine plankton. C. closterium and Nitzschia longissima may easily be confused under light microscope (LM) because detailed morphological features are not available.12 monoclonal cultures or isolates of benthic diatoms from Jiaozhou Bay were established in this study. Of them, 11 isolates were identified as C. closterium and one was identified as N. longissima var. reversa Grunow morphologically. The sequences of their nuclear-encoded small-subunit ribosomal RNA (SSU rDNA) gene and the chloroplast-encoded rbcL gene were determined. Very high sequence divergence of SSU rDNA and rbcL genes were found among the 11 isolates of C. closterium. The fragment of SSU rDNA gene was 1775bp in length and a total of 31 sites were variable. In all, 1190bp of rbcL gene were determined. Of these, 118 positions (9.9%) were variable, more than half (108 positions) occurred in third codon positions. Numerous nucleotide variations of rbcL gene resulted in relatively few amino acid variations. The sequences of SSU rDNA and rbcL genes determined from N. longissima var. reversa Grunow were 1777bp and 1190bp in length respectively, which showed very different from that of C. closterium.Neighbor-joining (NJ) phylogenetic trees based on SSU rDNA and rbcL gene...