17:15 〜 19:15
[BCG07-P05] New endosymbiotic dinoflagellates from Amphisorus kudakajimaensis (Foraminifera) in Okinawa
キーワード：有孔虫、渦鞭毛藻、共生藻、光共生
Large benthic foraminifera are highly abundant in coral reef ecosystems, where their calcification plays a crucial role in the production of calcium carbonate. They establish a photosymbiosis with multiple species of autotrophic microalgae based on interdependent nutrient exchange. These photosymbionts enable foraminifers not only to promote calcification but also to adapt to various environments depending on their photosynthetic capacity. The diversity of photosymbionts could expand foraminiferal distribution. However, the foraminifera-symbiotic algae relationships have been poorly investigated due to the complexity genetic analysis and morphological observation of these organisms because both are unicellular eukaryotes. This study found co-presences of symbiotic algae from a single specimen of large benthic foraminifer, Amphisorus kudakajimaenesis, and presented species descriptions based on molecular phylogeny and morphology of newly established strains.
We collected large benthic foraminiferal specimens, in particularly Amphisorus sp., from the coral reef in Onna Village, Okinawa, Japan. Four specimens of Amphisorus sp. were used for molecular phylogenetic analysis of the SSU (small subunit) rDNA to identify foraminiferal species. Other specimens were divided into halves to stimulate release of symbionts from the hosts after weaken of the hosts in glucose and casein medium, respectively. Symbiotic algae were released from two host individuals. Each alga specimen was isolated and washed with the medium in multiwell culture plates using capillary pipettes. We successfully established two morphologically distinct strains of symbiotic algae from Amphisorus specimens. All Amphisorus specimens were identified as Amphisorus kudakajimaensis. The molecular phylogenetic analysis of the LSU (large subunit) rDNA and ITS (internal transcribed spacer) sequences identified two symbiotic algae species: one was identified as Symbiodinium clade A and another was Scrippsiella sp. Both are reported for the first time as symbiotic algae of foraminifera. Moreover, our novel Scrippsiella sp. sequences formed a monophyletic clade with a high support value, but was distinct from other sister species, Scrippsiella hangoei. This indicates our Scrippsiella sp. strain has not been described among the genus Scrippsiella. Motile cells of Scrippsiella sp. stained with Calcofluor White M2R (Sigma-Aldrich) showed fluorescence of thecal plates, revealing that this strain is a thecate dinoflagellate. The SEM (Scanning Electron Microscope) observations will be required to analyze the thecal pattern for a detailed taxonomic characterization of Scrippsiella sp. Our findings show that symbiotic algae in large benthic foraminifera are more diverse rather than previous known.
We collected large benthic foraminiferal specimens, in particularly Amphisorus sp., from the coral reef in Onna Village, Okinawa, Japan. Four specimens of Amphisorus sp. were used for molecular phylogenetic analysis of the SSU (small subunit) rDNA to identify foraminiferal species. Other specimens were divided into halves to stimulate release of symbionts from the hosts after weaken of the hosts in glucose and casein medium, respectively. Symbiotic algae were released from two host individuals. Each alga specimen was isolated and washed with the medium in multiwell culture plates using capillary pipettes. We successfully established two morphologically distinct strains of symbiotic algae from Amphisorus specimens. All Amphisorus specimens were identified as Amphisorus kudakajimaensis. The molecular phylogenetic analysis of the LSU (large subunit) rDNA and ITS (internal transcribed spacer) sequences identified two symbiotic algae species: one was identified as Symbiodinium clade A and another was Scrippsiella sp. Both are reported for the first time as symbiotic algae of foraminifera. Moreover, our novel Scrippsiella sp. sequences formed a monophyletic clade with a high support value, but was distinct from other sister species, Scrippsiella hangoei. This indicates our Scrippsiella sp. strain has not been described among the genus Scrippsiella. Motile cells of Scrippsiella sp. stained with Calcofluor White M2R (Sigma-Aldrich) showed fluorescence of thecal plates, revealing that this strain is a thecate dinoflagellate. The SEM (Scanning Electron Microscope) observations will be required to analyze the thecal pattern for a detailed taxonomic characterization of Scrippsiella sp. Our findings show that symbiotic algae in large benthic foraminifera are more diverse rather than previous known.