Symbiochlorum hainanensis gen. et sp. nov. (Ulvophyceae, Chlorophyta) isolated from bleached corals living in the South China Sea

Abstract

Light/scanning electron/transmission microscopy-based morphological analyses and multiple nucleotide sequences-based molecular phylogenetic analyses are used to identify and assess the phylogenetic position of a new unidentified green alga isolated from bleached corals living in the South China Sea. This new unidentified green alga is a unicellular marine alga and has uninucleate vegetative cells and multiple chloroplasts with a pyrenoid. It can form aplanosporangium covered by cell walls and reproduces by releasing autospore. These features differ substantially from those of the two genera Ignatius and Pseudocharacium. Those two genera have been accommodated in the Ignatius clade. Nucleotide sequences of the nuclear small subunit ribosomal RNA gene (18S rRNA), internal transcribed spacer 2 of ribosomal RNA gene (ITS2) and ribulose-1,5 bisphosphate carboxylase/oxygenase large subunit gene (rbcL, partial) are obtained and compared with published green algal sequences. The results from the morphology, ultrastructure, and multiple nucleotide sequences data support the placement of the new unidentified green alga in Ulvophyceae. This new unidentified isolate is described as Symbiochlorum hainanensis gen. et sp. nov., a new sister lineage to the Ignatius clade, Ulvophyceae, Chlorophyta.

Ocean Acidification and Warming Lead to Increased Growth and Altered Chloroplast Morphology in the Thermo-Tolerant Alga Symbiochlorum hainanensis

“…Cultures of S. hainanensis (CCTCC M2018096), isolated from coral species Porites lutea in the tropical reef regions of the SCS (Gong et al, 2018(Gong et al, , 2019, were incubated in 250-ml Erlenmeyer flasks with 100 ml autoclaved artificial seawater medium (Formula grade A Reef Sea Salt, Formula, Japan) under an in situ temperature of 26 • C, light intensity of 90 µmol photon m −2 s −1 with a 12-h/12-h light/dark cycle. The cultures were shaken at least three times a day.…”

“…Cells of S. hainanensis in the mid-exponential phase under different conditions (A, H, AH, and C) were determined based on scanning electron and transmission electron microscopy observations according to our previous study (Gong et al, 2018).…”

“…Symbiochlorum hainanensis, a recently discovered unicellular alga affiliated with Ulvophyceae, is widely associated with corals in the tropical coral reef areas of the South China Sea (SCS), where the annual average temperature is approximately 26 • C (Gong et al, 2018(Gong et al, , 2019. The optimal growth temperature of this alga is approximately 32 • C ( Supplementary Figure 1), which is higher than that of coral-symbiotic Cladocopium spp.…”

Characterization of the chloroplast genome of Symbiochlorum hainanensis (Ulvophyceae, Chlorophyta) and its phylogenetic analysis

“…The genus Symbiochlorium has been reported firstly by Gong et al. ( 2018 ). So far, S. hainandiae has been only reported species within genus Symbiochlorum.…”

Molecular Phylogeny of Unicellular Marine Coccoid Green Algae Revealed New Insights into the Systematics of the Ulvophyceae (Chlorophyta)

“…This clade of the Ulvophyceae was described as order Ignatiales by Skaloud & Leliaert in Skaloud et al [ 32 ]. Gong et al [ 33 ] found, in marine habitat on bleached corals, a coccoid green alga, which exclusively reproduced by aplanospores, and described it as Symbiochlorum hainanensis . The phylogenetic analyses revealed that this species is sister to the Ignatiales.…”