title: In situ survey of life cycle phases of the coccolithophore Emiliania huxleyi (Haptophyta).
abstract: The cosmopolitan coccolithophore Emiliania huxleyi is characterized by a strongly differentiated haplodiplontic life cycle consisting of a diploid phase, generally bearing coccoliths (calcified) but that can be also non-calcified, and a non-calcified biflagellated haploid phase. Given most studies have focused on the bloom-producing calcified phase, there is little-to-no information about non-calcified cells in nature. Using field mesocoms as experimental platforms, we quantitatively surveyed calcified and non-calcified cells using the combined calcareous detection fluorescent in situ hybridization (COD-FISH) method and qualitatively screened for haploid specific transcripts using reverse transcription-PCR during E. huxleyi bloom successions. Diploid, calcified cells formed dense blooms that were followed by the massive proliferation of E. huxleyi viruses (EhVs), which caused bloom demise. Non-calcified cells were also detected throughout the experiment, accounting for a minor fraction of the population but becoming progressively more abundant during mid-late bloom periods concomitant with EhV burst. Non-calcified cell growth also paralleled a distinct window of haploid-specific transcripts and the appearance of autotrophic flagellates morphologically similar to haploid cells, both of which are suggestive of meiosis and sexual life cycling during natural blooms of this prominent marine phytoplankton species.
authors.affiliation: CNRS and Université de Pierre et Marie Curie (Paris 06), UMR 7144, EPPO team, Station Biologique de Roscoff, Roscoff, France. miguel.frada@weizmann.ac.il
authors.forename: Miguel J
authors.initials: MJ
authors.lastname: Frada
authors.forename: Kay D
authors.initials: KD
authors.lastname: Bidle
authors.forename: Ian
authors.initials: I
authors.lastname: Probert
authors.forename: Colomban
authors.initials: C
authors.lastname: de Vargas
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000235:genetics; D004171:Diploidy; D005068:Eutrophication; D006238:Haploidy; D058087:Haptophyta / Q000502:physiology* / Q000821:virology; D017404:In Situ Hybridization, Fluorescence; D008018:Life Cycle Stages / Q000502:physiology*; D010839:Phytoplankton / Q000502:physiology