Proline-rich peptide from the coral pathogen Vibrio shiloi that inhibits photosynthesis of Zooxanthellae.
The coral-bleaching bacterium Vibrio shiloi biosynthesizes and secretes an extracellular peptide, referred to as toxin P, which inhibits photosynthesis of coral symbiotic algae (zooxanthellae). Toxin P was produced during the stationary phase when the bacterium was grown on peptone or Casamino Acids media at 29 degrees C. Glycerol inhibited the production of toxin P. Toxin P was purified to homogeneity, yielding the following 12-residue peptide: PYPVYAPPPVVP (molecular weight, 1,295.54). The structure of toxin P was confirmed by chemical synthesis. In the presence of 12.5 mM NH(4)Cl, pure natural or synthetic toxin P (10 microM) caused a 64% decrease in the photosynthetic quantum yield of zooxanthellae within 5 min. The inhibition was proportional to the toxin P concentration. Toxin P bound avidly to zooxanthellae, such that subsequent addition of NH(4)Cl resulted in rapid inhibition of photosynthesis. When zooxanthellae were incubated in the presence of NH(4)Cl and toxin P, there was a rapid decrease in the pH (pH 7.8 to 7.2) of the bulk liquid, suggesting that toxin P facilitates transport of NH(3) into the cell. It is known that uptake of NH(3) into cells can destroy the pH gradient and block photosynthesis. This mode of action of toxin P can help explain the mechanism of coral bleaching by V. shiloi.
Department of Molecular Microbiology & Biotechnology, Tel Aviv University, Ramat Aviv, Israel 69978.
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Banin
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Khare
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Naider
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Rosenberg
D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D003063:Cnidaria / Q000382:microbiology*; D003470:Culture Media; D056890:Eukaryota / Q000187:drug effects / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010788:Photosynthesis / Q000187:drug effects*; D011392:Proline / Q000737:chemistry; D013559:Symbiosis; D014733:Vibrio / Q000254:growth & development / Q000378:metabolism*
D001427:Bacterial Toxins; D003470:Culture Media; D010455:Peptides; D011392:Proline