title: Isolation of clonal axenic strains of the symbiotic dinoflagellate Symbiodinium and their growth and host specificity(1).
abstract: The cnidarian-dinoflagellate mutualism is integral to the survival of the coral-reef ecosystem. Despite the enormous ecological and economic importance of corals, their cellular and molecular biology and the ways in which they respond to environmental change are still poorly understood. We have been developing a proxy system for examining the coral mutualism in which the dinoflagellate symbiont Symbiodinium is introduced into a clonal population of the host Aiptasia, a small sea anemone closely related to corals. To further develop the tools for this system, we generated five clonal, axenic strains of Symbiodinium and verified the lack of contaminants by growth on rich medium, microscopic examination, and PCR analysis. These strains were assigned to clades A (two strains), B, E, and F based on their chloroplast 23S rDNA sequences. Growth studies in liquid cultures showed that the clade B strain and one of the clade A strains were able to grow photoautotrophically (in light with no fixed carbon), mixotrophically (in light with fixed carbon), or heterotrophically (in dark with fixed carbon). The clade E strain, thought to be free-living, was able to grow photoautotrophically but not heterotrophically. Infection of an aposymbiotic Aiptasia host with the axenic strains showed consistent patterns of specificity, with only the clade B and one of the clade A strains able to successfully establish symbiosis. Overall, the Aiptasia-Symbiodinium association represents an important model system for dissecting aspects of the physiology and cellular and molecular biology of cnidarian-dinoflagellate mutualism and exploring issues that bear directly on coral bleaching.
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, 94305, USA.
authors.forename: Tingting
authors.initials: T
authors.lastname: Xiang
authors.affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, CA, 94305, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Hambleton
authors.affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, CA, 94305, USA.
authors.forename: Jan C
authors.initials: JC
authors.lastname: DeNofrio
authors.affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, CA, 94305, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Pringle
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, 94305, USA.
authors.forename: Arthur R
authors.initials: AR
authors.lastname: Grossman
keywords: algae; anemone; cnidarian; coral bleaching; symbiosis