BACTERIAL BLEACHING OF CORALS Vibrio shiloi/oculina patagonica model system Vibrio coralliilyticus/pocillopora damicornis model system Tel Aviv University Eugene Rosenberg Dept Molecular Microbiology & Biotechnology Amir Toren Tomer Israely Ehud Banin Yael Ben-Haim Leah Falkowitz Omry Koren Ariel Kushmaro Meir Sussman Yossi Loya Dept of Zoology Maoz Fine
Importance of Coral Reefs Most spectacular structures made by living organism Rich in species diversity High productivity Protects coastlines from erosion Economically important (fishing & tourism) Reservoir for new drugs
Diseases Of Corals Coral diseases have significantly increased over the last two decades, causing mass destruction of reefs throughout the world. ~ 30%% mortality worldwide
Coral Bleaching = loss of endosymbiotic algae (Zooxanthellae) High correlation with increased seawater temperature (global warming) Hypothesis 1: Heat stress on the coral causes it to expel the Zooxanthllae Hypothesis 2: Bleaching is an infectious disease
Partially bleached O. patagonica
Bleaching of the coral Oculina patagonica occurs regularly during the summer (FINE, KUSHMARO and ISRAELY) 35 30 25 20 15 10 5 0 Bleaching (%) Temperature Seawater temperature ( C) O 90 80 70 60 50 40 30 20 10 0 Bleaching (%) 8.00 6.00 4.00 2.00 12.99 10.99 6.99 3.98 11.97 9.97 7.97 4.97 12.96 9.96 7.96 5.96 12.95 Month and Year
V. shiloi is the causative agent of bleaching of O. patagonica Koch s postulates were applied. KUSHMARO ET AL 1996,1997
BLEACHING OF O. PATAGONICA AS A FUNCTION OF TEMPERATURE AND INOCULUM SIZE Vibrio shiloi (cells/ml) 0 120 Temperature ( o C) 29 29 Bleaching* (%) 0 95 0 16 0 10 2-10 8 16 0 * At 3 weeks
QUESTIONS 1. What are the mechanisms? 2. How does temperature affect the process? 3. How general is bacterial bleaching?
Adhesion Penetration Process of infection Multiplication and differentiation into the VBNC state Toxin production (PYPVYAPPPVVP) Role of superoxide dismutase (SOD) Transmission
Superoxide dismutase a virulence factor in V. shiloi The coral tissue during the day time is very rich in oxygen (>250% saturation). This can impose oxidative stress on internal bacteria. Superoxide dismutase plays an essential role in defense against the potential toxicity of oxygen. Superoxide dismutase O 2- + O 2-2H + H 2 O 2 + O 2 Catalase H 2 O 2 + H 2 O 2 2H 2 O + O 2
V. shiloi secretes a Superoxide Dismutase (SOD) which is temperature regulated 16 0 C 30 0 C 16 0 C 30 0 C PAGE SOD activity gel Banin et al. (2003)
V. shiloi SOD - mutant avirulent Adhesion Penetration 100 1.0E+10 80 1.0E+08 Adhesion (% ) 60 40 20 Wild type SOD Mutant Total count 1.0E+06 1.0E+04 1.0E+02 Wild Type SOD Mutent Mutant 0 1.0E+00 0 6 12 18 24 0 50 100 150 200 Time (h) Time after infection (h) A SOD - mutant adheres penetrates but then dies even at permissive temperature (30 0 C).
Conclusion Adhesion Survival in the tissue Superoxide-dismutase Toxin production Temperature dependent Temperature turns on virulence genes!
V. shiloi can not survive in O. patagonica in the winter. Thus, fresh infection is needed each spring. Where is V. shiloi in the winter?
FISH STAINING OF SECTIONS OF THE FIREWORM HERMODICE CARUNCULATA a b (Sussman et. al. 2003)
Presence of Vibrio shiloi in Hermodice caranculata. Worms were collected from different depths during the winter 2001/2002, crushed and analyzed for colony forming units (cfu) and total V. shiloi (FISH) Worm length Vibrio shiloi per worm Ratio (cm) cfu FISH (cfu/fish) 6 4.1 x 10 4 1.1 x 10 8 3.7 x 10-4 5 4.1 x 10 4 0.7 x 10 8 5.8 x 10-4- 13 18.3 x 10 4 2.9 x 10 8 6.3 x 10-4 7 7.8 x 10 4 0.6 x 10 8 1.3 x 10-4 7 8.8 x 10 4 1.3 x 10 8 6.8 x 10-4
BLEACHING OF O. PATAGONICA BY INFECTED H. CARUNCULATA 7 days 17 days (Sussman et. al. 2003)
The fireworm Hermodice carunculata feeding on O. patagonica: a reservoir and vector of V. shiloi. (Photograph by M. Fine)
How general is bacterial bleaching of corals?
Indirect evidence suggests that coral bleaching is an infectious disease! Patchy spatial distribution! Spreading nature highly symptomatic of an infectious disease
First direct evidence for bacterial bleaching in coral reefs: Bleaching of Pocillopora damicornis is a result of bacterial infection Zanzibar, Tanzania The Indian Ocean Ben-Haim & Rosenberg, 2002/3
Pocillopora damicornis bleached healthy
Vibrio coralliilyticus sectioned cell negatively stained
Bleaching of P. damicornis by Vibrio coralliilyticus at 24-25 o C Infected coral Control coral Koch s postulates satisfied
QUESTIONS AND CHALLENGES As the area of light increases, so does the circumference of darkness A. Einstein V. shiloi/o. patagonica: Nature of VBNC state? Temperature regulation of virulence genes? Generality of bacterial bleaching? How can coral diseases be controlled? What are the roles of indigenous coral bacteria in health and disease?