Trebonskia zoosporica, gen. et sp. nov., a new member of the Goniochloridales (Eustigmatophyceae, Stramenopiles) with an unusual mode of reproduction

ABSTRACT

A new freshwater microalgal isolate, CCALA 1135, was characterized using a polyphasic approach (morphology, ultrastructure, fatty acid composition, 18S rRNA gene and rbcL analyses). Non-motile vegetative cells were spherical with thick, smooth cell walls lacking ornamentation, with multiple overlapping chloroplasts and sometimes more than one red globule in the cytoplasm. The nuclear and chloroplast envelopes formed a continuous membrane and there was no pyrenoid. These morphological and ultrastructural features indicated assignment to the class Eustigmatophyceae. The strain was, however, unique in its mode of reproduction: only zoospores were formed, but no autospores were observed (i.e. obligate zoospory, which is rare in the Eustigmatophyceae). The zoospores were relatively fragile and their morphology was similar to those of other members of the clade Goniochloridales (a clade name under the PhyloCode) that have been studied, being uniflagellate and lacking an eyespot. A very high proportion of polyunsaturated fatty acids (up to 57% of total fatty acids) was found, dominated by nutritionally valuable arachidonic and eicosapentaenoic acids, the latter being the most abundant FA (up to 35%) in the total profile. Phylogenetic analysis based on 18S rDNA and rbcL sequences confirmed that CCALA 1135 represents a new member of Goniochloridales clade IIc. Based on cellular morphology, ultrastructure and molecular data we propose this strain as a new species and new genus of the Eustigmatophyceae, Trebonskia zoosporica gen. et sp. nov. Our work is a step toward clarifying the taxonomy of a group of the Eustigmatophyceae with many unnamed strains awaiting characterization.

Highlights

• A new genus and species of Eustigmatophyceae is described using a polyphasic approach.

• This isolate reproduces only by zoospores, a mode rare within Eustigmatophyceae.

• It contained a high proportion of nutritionally valuable polyunsaturated fatty acids.

KEYWORDS:

• 18S rRNA
• Eustigmatophyceae
• fatty acids
• Goniochloridales
• rbcL
• Trebonskia zoosporica
• zoospores

Author contributions

P. Přibyl: original concept, drafting, writing and editing manuscript, culture isolation, fatty acid analysis, LM, SEM and TEM; L. Procházková: drafting, writing and editing the manuscript, molecular laboratory work, phylogenetic analysis, LM and fluorescent microscopy.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2022.2089913

Supplementary figures S1–S7. Cell morphology of Trebonskia zoosporica. Figs S1–S3. Cells growing on a 2% agar plate, Figs S4–S7. The same population of cells under higher magnification, arrowhead shows mother cell before zoosporangium formation. Scale bars: Supplementary figs S1–S3, 20 µm; Figs S4–S7, 10 µm.

Supplementary video S1. Zoospore release from a two-cell zoosporangium (from 9 s) and its movement. Another moving zoospore appearing (20–28 s). Total time 34 s.

Supplementary video S2. A single zoospore life history showing gradual rounding and movement reduction of the cell. The video was edited from a longer recording (about 4 min). Total time 1 min 31 s.

Additional information

Funding

This work was supported by the Technology Agency of the Czech Republic, project No: TE01020080 and TN01000048, by long-term research development project No. RVO 67985939 of the Czech Academy of Sciences, and by Charles University Research Centre program No. 204069. Furthermore, this research was supported by the Czech Ministry of the Education, Youth and Sports, project LTAIN19139.