Spongiosarcinopsis qinghaiensis Q. YAN & G. LIU, 2022

Yan, Qiufeng, Zhu, Huan, Fang, Jiao, Liu, Benwen & Liu, Guoxiang, 2022, Taxonomic study of a novel terrestrial alga, Spongiosarcinopsis qinghaiensis sp. nov. (Protosiphonaceae, Chlorophyta), from the Qinghai-Tibet Plateau, PhytoKeys 204, pp. 83-95 : 83

Spongiosarcinopsis qinghaiensis Q. YAN & G. LIU sp. nov.

Description.

Found on the soil surface around brackish lakes. Unicellular, spherical (Figs 1 , 2 ), and cell diameter of 6-15 μm. Mature cells often divide into two cells by means of diads (Fig. 3 ). Cells contain one net-like chloroplast (Fig. 6 ), lateral, almost filling the entire cell at maturity (Figs 2 , 8 ), one nucleus, and one pyrenoid covered by starch envelope, although not obvious (Figs 7 , 8 ).

The vegetative cell wall is rough and there is an unidentified gelatinous layer outside the cell wall (Fig. 9 ). The pyrenoid is covered with a segmented starch envelope and penetrated by straight thylakoids (Fig. 10 ).

Asexual reproduction is achieved through diads or release of aplanospores (Figs 3-5 ). Aplanosporangia contain eight to 16 spherical aplanospores, and the release process can be observed (Figs 4 , 5 ). No sexual reproduction was observed.

Etymology.

The species epithet refers to the Holotype locality (Qinghai Province).

Type locality.

Qinghai Lake National Nature Reserve (37°02'N, 100°44'E), Qinghai Province, China; on soil surface.

Iconotype.

Fig. 2 .

Holotype.

QH2015 (HBI), collected by Qiu-Feng Yan and Huan Zhu, 22 September 2020; deposited in the Freshwater Algal Herbarium (HBI), Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei Province, China.

Distribution.

At present, the algal isolate is only found in China. It grows on loose and moist soil surfaces around brackish lakes.

Authentic culture.

Culture strain FACHB-3451 is deposited in the Freshwater Algae Specimen Station, Institute of Hydrobiology, Chinese Academy of Sciences (http://algae.ihb.ac.cn/).

Therefore, Spongiosarcinopsis qinghaiensis was found to be different from Spongiosarcinopsis terrestris , with respect to young cell shape, habitat, size of vegetative cells, and number of pyrenoids. Registration. http://phycobank.org/103211.

Phylogenetic analyses

The 18S rDNA alignment applied 45 sequences (including 15 Protosiphonaceae sequences), which consisted of 1686 sites, out of which 300 (17.8%) and 208 (12.3%) were variable and parsimony-informative sites, respectively. Nineteen ITS sequences were used for alignment and 546 sites, out of which 327 (59.9%) and 232 (42.5%) were variable and parsimony-informative sites, respectively. Table 1 presents detailed information about the alignment and nucleotide substitution in 18S rDNA and ITS concatenated phylogenies for molecular phylogenetic analysis.

The phylogenetic tree was constructed using the Bayesian approach based on 18S rDNA and ITS alignments (Figs 11 , 12 ), with the Bayesian posterior probabilities and ML bootstrap support reported. The topology of our 18S rDNA phylogeny (Fig. 11 ) is essentially consistent with that reported in previous studies ( Temraleeva et al. 2017). The tree based on 18S rDNA showed a strong Spongiosarcinopsis clade, comprising the algal strains isolated in the present study; hence, the algal isolates were classified into the genus Spongiosarcinopsis (Fig. 11 ). The tree based on ITS sequences prsesented the interspecific relationships within the genus Spongiosarcinopsis , and the algal strain isolated in the present study formed a distinct branch separate from Spongiosarcinopsis terrestris (Fig. 12 ).

ITS2 secondary structure

The ITS2 secondary structure was annotated, and two Spongiosarcinopsis strains were detected (Fig. 13 ), namely, Spongiosarcinopsis terrestris (MF687232) and Spongiosarcinopsis qinghaiensis (OM333733). The differences between the two strains of algae were compared. Three CBCs and four hemi-compensatory base changes (h-CBCs) were detected between the two strains.

Figures

Figure 11. Phylogenetic tree constructed by Bayesian approach based on 18 S rDNA sequences. Maximum likelihood bootstrap values and Bayesian posterior probabilities are given on nodes. Values above 0.50 for BI and 50 for ML are given. The gray part shows the new species of this study.

Figure 12. Phylogenetic tree constructed by Bayesian approach based on ITS sequences. Maximum likelihood bootstrap values and Bayesian posterior probabilities are given on nodes. Values above 0.50 for BI and 50 for ML are given. The gray part shows the new species of this study.

Figure 13. The ITS 2 secondary structure between the two strains in Spongiosarcinopsis. The darker the color, the more significant the variation. Differences between the two species have been indicated by arrows in the figure, red for CBCs and blue for h-CBCs.

Figures 1 - 6. Culture sample morphology of Spongiosarcinopsis qinghaiensis sp. nov.: 1 the normal growth state of the algal strain, young cells have a larger protein nucleus 2 mature vegetative cells 3 vegetative cells reproduce through diads 4 aplanosporangia containing aplanospores covered by thin cell walls 5 aplanospores released from aplanosporangia 6 net-like chloroplast under fluorescence. Scale bar: 10 μm (1 - 4); 5 μm (5 - 6).

Figures 7 - 10. TEM images of Spongiosarcinopsis qinghaiensis sp. nov.: 7 cells contain one nucleus, one chloroplast, one pyrenoid covered by starch envelope 8 the starch envelope covering the pyrenoid is not obvious 9 unidentified gelatinous layer outside the cell wall 10 the pyrenoid is covered by segmented starch envelope and penetrated by straight thylakoids. C = chloroplast, N = nucleus, P = pyrenoid, SE = starch envelope of the pyrenoid, W = cell wall. Arrows indicate thylakoids penetrating into the pyrenoid matrix. Scale bar: 1 μm (7, 8, 10); 500 nm (9).