A comparative ultrastructure, physiology and phylogeny of two Tetraselmis species isolated from Australian waters
Creators: name: Mazid, Mohammed Abdul
Publisher: name: Charles Darwin University
Year: 2009

description: Phytoplankton, also known as microalgae, is single cell photosynthetic protists that live floating in sea, oceans and the lakes. They have the ability to photosynthesize by trapping sunlight energy and convert carbon dioxide into organic carbon compounds. They are therefore considered the base of the aquatic food web, providing an ecological function for all aquatic life form and contributing about 90% of the Earth’s oxygen. The taxonomy of phytoplankton is diverse, consisting of Cyanophyta (now classified with the bacteria), Prochlorophyta, Chlorophyta, Chrysophyta, Rhodophyta, Pyrrophyta, Cryptophyta and Euglenophyta. The work described in this thesis was concentrated in Tetraselmis species which belong to the class Prasinophyceae under the division Chlorophyta. Tetraselmis play important roles in ecology of aquatic and terrestrial ecosystems and have been used as model protists in physiological, biochemical and environmental studies. Tetraselmis species also play an important role in aquaculture. Two strains of Tetraselmis, namely NT18 and CS317, potentially important in aquaculture, were selected for this work: NT18 was isolated from Darwin Harbour, northern Australia and CS317 was isolated from Moreton Bay, South-East Australia. The aim of the present investigation was to find the similarities and differences of the two isolates in terms of their growth, pigment characteristics, morphology, ultrastructures, and phylogeny, using standard protocol of light microscope, scanning electron microscope, transmission electron microscope, nuclear SSU rRNA sequences, plastid rbcL gene sequence, growth studies and pigment profile with a view to proper identify them for future work in aquaculture nutrition. The main findings were: 1. The NT18 cells were on an average approximately 7-9 μm in length, and 6-7 μm in width and the CS317 cells were on an average 9-12 μm in length and 6-8μm in width. 2. NT18 and CS317 had the same pyrenoid structure and were characterized by the presence of several canaliculi ending blindly in the pyrenoid matrix. 3. NT18 possesses single layer of eyespot and CS317 possesses double layer of eyespot. 4. NT18 and CS317 had the same flagellar hair type (type 1) but different sub-type. NT18 has subtype 1b with 18 distal subunits and a distal filament of about 200 nm in length. CS317 has subtype 1c with 33 distal subunits and no distal filament. 5. They had the same pigment profile, consisting of Chlorophylide a, Neoxanthin, Violaxanthin, Lutein, Unknown carotenoid, Chlorophyll b, Chlorophyll a, and β- Carotene. 6. Strains NT18 and CS317 formed a clade with other Tetraselmis species with high bootstrap values in analyses of rbcL and SSU sequences. On the basis of the results obtained, NT18 and CS317 were found to possess enough different characteristics from each other, and from known Tetraselmis species. For these reasons, they constitute different species. The organisms have been tentatively assigned as Tetraselmis casuarinaca sp. nov. and T. moretonica sp. nov. (Chlorodendrales, Prasinophyceae, Chlorophyta), respectively.