Aurantiochytrium acetophilum strain:HS399 Genome sequencing and assembly. Aurantiochytrium acetophilum strain:HS399

A new species of Aurantiochytrium (Thraustochytriaceae) from a mangrove swamp (Florida, USA) was described. Vegetative cells commonly divided to produce tetrads of cells that separated and grew in size. Cells were surrounded by a cell wall composed of organic scales. Vegetative cells transferred to seawater without organic nutrients formed cysts. Under nutrient limitation, stationary phase cells filled with lipid vacuoles. Vegetative cells produced sporogenous cell masses when repeatedly transferred to fresh culture medium. Sporogenous cells gave rise to amoebae, amoebosporangia and two types of zoosporangia. Some amoebae rounded up and later gave rise to amoebosporangia; other amoebae became multinucleate with four nuclei and then divided into four spherical cells; some four nucleate amoebae rounded up and produced an amoebosporangium. Rarely, amoeoboid cells with eight nuclei were observed. Biflagellate swimming cells had flagella inserted laterally, approximately one third from the anterior end. Type I sporangia had 8, 16 or 32 cells and arose from sporogenous cells. The zoospores were elongate and then becoming pyriform to round, sometimes connected to other zoospores by cytoplasmic strands. Type II sporangia had a large central cell that pinched off small spherical swimming cells, which may have been gametes. Putative gametes fused together to form a zygote but the zygote fate and meiosis were not determined. Physiological studies showed that the cells utilized acetate and many other organic compounds. Molecular phylogenetic analysis of the 18S rRNA gene demonstrated that the new organism was different from A. limacinium. The entire genome was sequenced and compared to other thraustochytrids. Meiosis genes were found in the genome.