title: Coral host cells acidify symbiotic algal microenvironment to promote photosynthesis.
abstract: Symbiotic dinoflagellate algae residing inside coral tissues supply the host with the majority of their energy requirements through the translocation of photosynthetically fixed carbon. The algae, in turn, rely on the host for the supply of inorganic carbon. Carbon must be concentrated as CO2 in order for photosynthesis to proceed, and here we show that the coral host plays an active role in this process. The host-derived symbiosome membrane surrounding the algae abundantly expresses vacuolar H(+)-ATPase (VHA), which acidifies the symbiosome space down to pH ∼ 4. Inhibition of VHA results in a significant decrease in average H(+) activity in the symbiosome of up to 75% and a significant reduction in O2 production rate, a measure of photosynthetic activity. These results suggest that host VHA is part of a previously unidentified carbon concentrating mechanism for algal photosynthesis and provide mechanistic evidence that coral host cells can actively modulate the physiology of their symbionts.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Katie L
authors.initials: KL
authors.lastname: Barott
authors.affiliation: Marine Biology Department, Centre Scientifique de Monaco, MC-98000 Monaco, Monaco; and Laboratoire Européen Associé 647 "Biosensib," Centre Scientifique de Monaco-Centre National de la Recherche Scientifique, MC-98000 Monaco, Monaco.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Venn
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Sidney O
authors.initials: SO
authors.lastname: Perez
authors.affiliation: Marine Biology Department, Centre Scientifique de Monaco, MC-98000 Monaco, Monaco; and.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Tambutté
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093; mtresguerres@ucsd.edu.
authors.forename: Martin
authors.initials: M
authors.lastname: Tresguerres
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D037421:Anthozoa / Q000235:genetics / Q000378:metabolism* / Q000469:parasitology*; D002244:Carbon / Q000378:metabolism; D004141:Dinoflagellida / Q000378:metabolism*; D017753:Ecosystem; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D008969:Molecular Sequence Data; D010788:Photosynthesis / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis / Q000502:physiology*; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism
chemical_list: D002244:Carbon; D025262:Vacuolar Proton-Translocating ATPases
keywords: Symbiodinium; V type H+ ATPase; carbon concentrating mechanism; proton pump; zooxanthellae