Morphological and molecular comparison of three centric diatoms (Bacillariophyceae: Chaetoceros) isolated from the coast of Eastern Thailand

The objective of this study was to identify Chaetoceros species using microscopic observations, sequence analysis of 18S rDNA, random amplified polymorphic DNA (RAPD) barcoding and nuclear magnetic resonance (NMR) spectroscopy. Chaetoceros were obtained from three different algae laboratories: Center of Excellence for Marine Biotechnology (CEMB), Chanthaburi Coastal Fisheries Research and Development (CHAN) and Institute of Marine Science, Burapha University (BIM). Genomic DNA for the RAPD analysis was extracted using the phenol-chloroform method, followed by 18S rDNA amplification. The 18S rDNA sequence analysis showed that Chaetoceros CEMB was most similar to C. gracilis (e-value = 0.0, identity = 98%), Chaetoceros CHAN was most similar to C. debilis (e-value = 0.0, identity = 99%) and Chaetoceros BIM was most similar to C. debilis (e-value = 0.0, identity = 98%). The RAPD results revealed differences in the three Chaetoceros isolates with polymorphisms between 30.43% and 60.00%, and Chaetoceros CEMB showed high polymorphic bands. Scanning electron microscopy revealed that Chaetoceros CEMB were larger and had larger setae compared with the other isolates (P < 0.05). The results of the NMR characterization of metabolites were consistent with the results of the sequence and morphological analyses. The concentrations of several metabolites, including chlorophyll c 1 , chlorophyll a, myo-inositol, fucoxanthin, astaxanthin, lutein and zeaxanthin, were lower in Chaetoceros CEMB than in Chaetoceros BIM and CHAN. However, high concentrations of fatty acids, such as oleic acid, linoleic acid, α-linolenic acid and arachidic acid, were observed in all isolates. Generally, the results of this study will aid future studies examining the diversity of Chaetoceros in various culture environments.