Isolation And Characterization Of Coccolithphores And The Physiological Response To Ocean Acidification And High Light

Coccolithophores are unicellular marine phytoplankton with a calcareous shell in a specific life history,belonging to the phylum Haptophyta,which plays an important role in biogeochemical cycles and global climate regulation.There was no efficient barcode for molecular identification of Haptophyta in the isolation and identification of coccolithophores.With the large amount of carbon dioxide emission,ocean acidification and enhanced solar irradiation and other environmental factors had influenced the growth,photosynthesis and calcification of coccolithophores.The phylogenetic analysis of the isolated algal strains from the coastal zone of Yantai was performed by cox3,16S,28S and tuf A gene sequences,verified by DNA barcoding method and identified taxonomically.The results showed that the mitochondrial gene cox3could be used as a potential DNA barcode for the algae,while the other genes were not of high resolution.Emilinia huxleyi is the main model species in the study of coccolithphores.Physiological and transcriptional analyses of calcified cells of E.huxleyi PERU41 compared to non-calcified cells showed that non-calcified cells had a greater proliferative capacity.Genes related to PIC content,microtubules and microtubule proteins related to physiological processes were upregulated in calcified cells.Non-calcified cells increased their light capture capacity by increasing cytochrome content,and increased carotenoid content indicated that non-calcified cells lost their calcified shells to dissipate the excess light energy captured mainly through the lutein cycle involving carotenoids,protecting the photosynthetic structures of the cells.In order to study the physiological response of coccolithphores under ocean acidification two different genotypes of E.huxleyi PERU41 and PERU46 were experimented at different CO₂ concentrations(400 ppmv,1000 ppmv).The results revealed significant differences in the growth and calcification levels between PERU41 and PERU46(P<0.05).PERU46 had a higher growth rate indicating a greater proliferation capacity.Scanning electron microscopy results,particulate inorganic carbon and carbonate chemistry systems all indicated that PERU41 had a stronger calcification ability.Under seawater acidification,the growth rate of both E.huxleyi decreased significantly,and the relatively weaker calcification of PERU41 decreased more than the stronger calcification ability of PERU41,and the high CO₂ concentration had a negative effect on the granulite algal cells.Under the conditions of acidification and short-term high light coupling,the non-photochemical quenching of PERU46 was significantly higher than that of PERU41,while the calcification of PERU41 was significantly higher than that of PERU46.This indicated that the two genotypes of E.huxleyi had different strategies to cope with high light stress under acidification conditions,with PERU46 acting mainly by enhancing calcification to produce a thicker calcareous shell to shade out high light and PERU46 by increasing calcification.PERU46 responded to high light stress mainly by increasing non-photochemical quenching.