Figure 1.
Cells were observed by differential interference contrast microscopy. (A) Vegetative cells are single and ellipsoidal. Each cell typically has a single bright green parietal chloroplast with a pyrenoid (arrowhead) that occupies half of the cell periphery and there is no flagella. (B) A cell which contains a single chloroplast. (C) A cell which contains two divided chloroplasts. (D) Sporangium with two autospores. (E) Sporangium with four autospores. (F, G) Sporangium with eight autospores. Scale bars: 5 µm (A); 2 µm (B–G).
Figure 2.
Phylogenetic position of YKT1.
Phylogenetic trees based on the 18S rDNA (A) and plastid 16S rDNA sequence (B) are shown. The trees were constructed by a maximum-likelihood method (RaxML 7.2.8) [24]. Maximum likelihood bootstrap values (ML) >50% by RaxML and bayesian posterior probabilities (BI) >0.7 by the Bayesian analysis (MrBayes 3.1.2) [25] are shown above the branches. The accession numbers of the sequences are shown along with the names of the species. The lineage designation follows [31]. The branch length reflects the evolutionary distances indicated by the scale bar.
Figure 3.
Growth of YKT1 under various pH and temperature conditions.
(A) Photograph of the culture (1 day after the onset of culture at the indicated pH) and the growth rate based on increase in the cell number (open bars) and OD750 (solid bars) at the indicated pH and 25°C. (B) Micrographs showing the cells cultured at the indicated pH (from pH 1.0 to pH 7.0). The arrowheads indicate dividing cells. (C) Photograph of the culture (1 day after the onset of culture at the indicated temperature) and the growth rate based on the increase in the cell number (open bars) and OD750 (solid bars) at the indicated temperature and pH 3.0. (D) Micrographs showing cells cultured at the indicated temperature (from 10 to 35°C). The arrowheads indicate dividing cells. Scale bars: 5 µm (B, D).
Figure 4.
Accumulation of lipid droplets under the nitrogen-depleted condition (pH 3.0, 25°C).
(A) Growth curves of YKT1 under nitrogen-replete (+N) or nitrogen-depleted (–N) conditions. (B) Photographs of the cultures under +N or –N conditions at 0 and 7 days after the onset of cultivation. (C) Time course of storage lipid accumulation under +N or –N conditions. Lipid droplets were stained with BODIPY (green fluorescence) and cells were observed under fluorescence microscopy. (D) Micrographs of cells that were cultured under the +N or –N conditions for 7 days. Images were obtained by differential interference contrast microscopy (DIC), BODIPY staining (BODIPY), chlorophyll autofluorescence (Chl), and merged images of BODIPY and Chl (Merged) are shown. (E) Storage lipid content (% of dry weight) in YKT1 cultured under +N or –N conditions for 7 days was determined by the Nile Red method [27]. The bars indicate the standard deviation of three individual experiments. Scale bars: 5 µm (C); 2 µm (D).
Table 1.
Physiolohical features of strain YKT1.