Trachydiscus guangdongensis sp. nov., a new member of Eustigmatophyceae (Stramenopiles) isolated from China: morphology, phylogeny, fatty acid profile, pigment, and cell wall composition

The microalgal strain, JNU5, was isolated downriver from the Hengshishui River of the Guangdong Province, China. The morphology of JNU5 revealed that it was a spherical, unicellular organism with a smooth cell wall. The cell contained a large vacuole and prominent, reddish globule. The pigment composition revealed that chlorophyll a was the only chlorophyll, and violaxanthin was the predominant carotenoid along with vaucheriaxanthin-ester and β-carotene. The fatty acid profile of JNU5 mainly consisted of myristic acid, palmic acid, linoleic acid, and eicosapentaenoic acid (EPA). Moreover, the EPA content consisted of up to 40% of total fatty acids. Phylogeny was determined using the 18S rDNA sequences suggested that JNU5 was a member of Eustigmatophyceae, belonging to Clade IIa and was close to Trachydiscus minutus. T. minutus and JNU5 were easily distinguished by cell shape and size. This indicates that JNU5 is a new species, and thus, we have named it, Trachydiscus guangdongensis sp. nov.. Meanwhile, the cell wall composition of JNU5 was analyzed and was found to be mainly composed of galactose (66%) with some glucose and mannose present. The water-soluble polysaccharide (WSP) of the cell wall was primarily composed of galactose, which accounted for 90% of total sugar.