Involvement of Acidic Polysaccharide Ph-PS-2 and Protein in Initiation of Coccolith Mineralization, as Demonstrated by In Vitro Calcification on the Base Plate
Coccolithophorids, unicellular marine microalgae, have calcified scales with elaborate structures, called coccoliths, on the cell surface. Coccoliths generally comprise a base plate, CaCO3, and a crystal coat consisting of acidic polysaccharides. In this study, the in vitro calcification conditions on the base plate of Pleurochrysis haptonemofera were examined to determine the functions of the base plate and acidic polysaccharides (Ph-PS-1, -2, and -3). When EDTA-treated coccoliths (acidic polysaccharide-free base plates) or low pH-treated coccoliths (whole acidic polysaccharide-containing base plates) were used, mineralization was not detected on the base plate. In contrast, in the case of coccoliths which were decalcified by lowering of the pH and then treated with urea (Ph-PS-2-containing base plates), distinct aggregates, probably containing CaCO3, were observed only on the rim of the base plates. Energy dispersive X-ray spectroscopy (EDS) confirmed that the aggregates contained Ca and O, although X-ray diffraction analysis did not reveal any evidence of crystalline materials. Also, in vitro mineralization experiments performed on EDTA-treated coccoliths using isolated acidic polysaccharides demonstrated that the Ca-containing aggregates were markedly formed only in the presence of Ph-PS-2. Furthermore, in vitro mineralization experiments conducted on protein-extracted base plates suggested that the coccolith-associated protein(s) are involved in the Ca deposition. These findings suggest that Ph-PS-2 associated with the protein(s) on the base plate rim initiates Ca2+ binding at the beginning of coccolith formation, and some other factors are required for subsequent calcite formation.
KeywordsAcidic polysaccharide Calcification Calcium Coccolithophorid Pleurochrysis haptonemofera Urea-extraction
We are grateful to Dr. I. Inouye of Tsukuba University for kindly providing the P. haptonemofera cells, to Drs. Y. Hirokawa of Tokyo University of Pharmacy and M. Kawachi of NIES for the excellent scanning electron micrographs of the cells and hearty encouragement, and to Mr. N. J. Halewood for correcting the English version of this paper.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
- Fujiwara S, Tsuzuki M (2011) Coccolith formation in the Haptophyta. In: Kersey WT, Munger SP (eds) Marine phytoplankton. Nova Science Publishers, New YorkGoogle Scholar
- Fujiwara S, Hirokawa Y, Takatsuka Y, Suda K, Asamizu E, Takayanagi T, Shibata D, Tabata S, Tsuzuki M (2007) Gene expression profiling of coccolith-bearing cells and naked cells in haptophyte Pleurochrysis haptonemofera with a cDNA macroarray system. Mar Biotechnol 9:550–560CrossRefPubMedGoogle Scholar
- Hirokawa H, Fujiwara S, Tsuzuki M (2005) Three types of acidic polysaccharides associated with coccolith of Pleurochrysis haptonemofera: comparison of the biochemical characteristics with those of P. carterae and analysis using fluorescein-isothiocyanate-labeled lectins. Mar Biotechnol 7:634–644CrossRefPubMedGoogle Scholar
- Hirokawa Y, Matsuzuka S, Itayama S, Uchida T, Fujiwara S, Ozaki N, Nagasawa H, Tsuzuki M (2013) Localization and associative strength of acid polysaccharides in coccoliths of Pleurochrysis haptonemofera (Haptophyta) predicted from their extractability from partially decalcified coccoliths. Open J Mar Sci 3:48–54CrossRefGoogle Scholar
- Ozaki N, Ikazaki M, Kogure T, Sakuda S, Nagasawa H (2004) Structural and functional diversity of acidic polysaccharides from various species of coccolithophorid algae. Thalassas 20:61–70Google Scholar
- Takahashi J, Fujiwara S, Kikyo M, Hirokawa Y, Tsuzuki M (2002) Discrimination of the cell surface of the coccolithophorid Pleurochrysis haptonemofera from light scattering and fluorescein-isothiocyanate-labeled lectin staining measured by flow cytometry. Mar Biotechnol 4:94–101CrossRefPubMedGoogle Scholar