Aplanochytrium minuta ( Watson and Raper, 1957 )

Park, Dong Hyuk Jeong and Jong Soo, 2021, Characterizations of five heterotrophic nanoflagellates newly recorded in Korea, Journal of Species Research 10 (4), pp. 356-363 : 359-360

3. Aplanochytrium minuta ( Watson and Raper, 1957)

Leander and Porter, 2000 ( Fig. 2A, B )

Synonym: Labyrinthuloides minuta Watson and Raper, 1957 .

Isolation. Dong Hyuk Jeong and Jong Soo Park performed specimen collection on 15 September 2020, from the Yeongildae Beach (36°03′49.00″N, 129°23′12.12″E), Pohang , Korea. Temperature: 24.9℃, Salinity: 29.9 PSU, pH: 7.7 .

Morphological description. The live strain PH 004 was ovoid to elliptical-shaped, but with the posterior end of the cell was more pointed than the anterior end ( Fig. 2A ,

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B). The average length and width of the cell body were 4.3±1.2 μm (mean±STD) and 2.9±1.1 μm, respectively (n = 20). Cells had spindle forms during actively gliding motility ( Fig. 2A ). Cells also had two unequal flagella. The average length of the anterior and posterior flagellum was 1.9±1.3 μm and 5.1±0.7 μm, respectively (n = 20). Furthermore, the anterior flagellum created the movement of a stiff flicker, while the posterior flagellum trailed posteriorly.

Molecular phylogeny. The partial 18S rDNA sequence of the strain PH 004 was 873 bp long (G + C content: 41%). The closest sequence retrieved by BLASTn search from GenBank was that of 18S rDNA sequence of Aplanochytrium minuta (formerly Labyrinthuloides minuta , accession number; L27634, 1,802 bp long, G + C content: 43%), with a high identity of 99.89% (872/873 bp). Additionally, the molecular phylogenetic tree of the 18S rDNA sequences placed the strain PH 004 within the A. minuta clade with a high bootstrap value (ML: 94%) and a posterior probability of 1 ( Fig. 2C ).

Remarks. The strain PH 004 is morphologically indistinguishable from the original A. minuta . The original cells were oval, cuneiform, or spherical-shaped ( Perkins, 1974). Also, the original cells were 5-10 μm in length, and 3-5 μm in width. It seems that the cell size of our isolate is smaller than that of the original A. minuta . Furthermore, like the strain PH 004, the original biflagellate cells displayed gliding motility, and sometimes the spindleshaped cells formed a sorus ( Watson and Raper, 1957; Raghukumar, 2002). The original A. minuta was spread as a monolayer on the agar surfaces, although we did not observe this monolayer. Phylogenetic trees of the 18S rDNA sequences showed clearly that the strain PH 004 was a member of previously known A. minuta . Overall, the strain PH 004 is speculated to be among the A. minuta strains in terms of morphology and molecular sequencing.

Habitat. Surface water/sediment interface of coastal areas. Specimen deposition. National Institute of Biological Resources, Korea (KPZXPR0000000022-KPZXPR0000 000026).

Identifiers. Dong Hyuk Jeong and Jong Soo Park.

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Figures

Fig. 2. (A, B) General light micrographs and sketch of Aplanochytrium minuta (formerly Labyrinthuloides minuta) strain PH004. AF: anterior flagellum, PF: posterior flagellum, scale bar=5 μm. All micrographs are differential interference contrast (DIC) images. (C) Maximum likelihood phylogenetic tree inferred from the 18S rDNA sequences of Labyrinthulomycetes (class) species including Aplanochytrium minuta strain PH004 and outgroup (Wobblia lunata and Placidia cafeteriopsis). Bootstrap support values (>80%) are shown at the nodes. Solid circles indicate a Bayesian posterior probability of 1 (posterior probability<0.95 not shown).