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RANJEET BHAGOOLI

Photosynthetic responses of genetically distinct isolated Symbiodinium spp. from marine symbioses to thermal and/or light stresses. RANJEET BHAGOOLI. Department of Biosciences, Faculty of Science, University of Mauritius, Reduit, Mauritius. INTRODUCTION.

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RANJEET BHAGOOLI

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  1. Photosynthetic responses of genetically distinct isolated Symbiodinium spp. from marine symbioses to thermal and/or light stresses RANJEET BHAGOOLI Department of Biosciences, Faculty of Science, University of Mauritius, Reduit, Mauritius

  2. INTRODUCTION • Reef-building corals harbor photosynthetic, unicellular, endosymbiotic dinoflagellates commonly known as zooxanthellae. • Ample evidence exist for diversity of zooxanthellae in reef corals. • Coral bleaching, whereby loss of zooxanthellae or their pigments occur, has been reported to increase in frequency and has been especially linked to high temperature anomalies. • In several studies, damage to photosynthetic apparatus of zooxanthellae have been associated with bleaching occurrences.

  3. During coral bleaching events differential bleaching susceptibilities among corals has been documented and this could be due to differential photo-physiological damage occurring in different symbiont types. • However, the photo-phyisiological responses of different types of isolated zooxanthellae to thermal stress has yet to be thoroughly investigated.

  4. HYPOTHESES • Photo-physiological responses of symbionts isolated from 9 host species (1 tridacnid, 1 anemone and 7 corals) are different • Types of symbionts isolated from the 9 hosts are different

  5. OBJECTIVES • Carry out temperature and/or light exposure experiments to assess the maximum quantum yield of PSII of symbionts isolated from 9 hosts. • Determine the ITS2 types of symbionts harbored by the respective hosts. • Correlate physiological responses with types of zooxanthellae isolated from the 9 host species under study.

  6. PRINCIPLE OF CHLOROPHYLL FLUORESCENCE TECHNIQUE Bioimaging of plant and fungal metabolism (http://www.shef.ac.uk/~ifpm/chlorophyll.html#anchor43692)

  7. PHYSIOLOGICAL ASSESSMENT USING PULSE AMPLITUDE MODULATION (PAM) FLUOROMETER Maximum quantum yield: Fv/Fm=(Fm-Fo)/Fm Relative = After treatment Before treatment

  8. Zooxanthellae typing • Ribosomal DNA amplification Forward primer ITS1 ITS2 SSUrDNA LSUrDNA Reverse primer + GC clamp • Denaturing Gradient Gel Electrophoresis (DGGE) GC clamp Low denaturant ITS2 Type1 ITS2 Type2 High denaturant Lajeunesse

  9. METHODOLOGY Hosts (n = 3-4 colonies): Tridacna spp., Aiptasia spp., Acropora microphthalma, Pocillopora damicornis, Stylophora pistillata,Platygyra ryukyuensis, Pachyseris rugosa, Galaxea facicularis, Pavona varians Galaxea fascicularis Isolated Hz. Zx. on filter Physiological assessment Symbiont ITS2 type determination DGGE profiles/ Sequencing Exposure at 26, 29, 32, 34oC and/or 0, 110, 170 mol m-2 s-1for 6 and 12h PAM fluorometer: Photosystem II activity (Fv/Fm) Match physiological responses to elevated temp. to symbiont ITS2 type

  10. PHOTO-PHYSIOLOGICAL RESPONSES (6h) OF ISOLATED SYMBIONTS FROM 9 HOSTS Relative Fv/Fm Hosts

  11. PHOTO-PHYSIOLOGICAL RESPONSES (12h) OF ISOLATED SYMBIONTS FROM 9 HOSTS Relative Fv/Fm Hosts

  12. EXAMPLES OF DGGE PROFILES * * * * * From LaJeunesse et al. 2005

  13. ITS2 TYPES OF SYMBIONTS FROM 9 HOSTS

  14. STATISTICAL RESULTS FOR EFFECTS OF STRESSES ON Fv/Fm

  15. H I E R A R C H I C A L C L U S T E R A N A L Y S I S Dendrogram using Average Linkage (Between Groups) Rescaled Distance Cluster Combine C A S E 0 5 10 15 20 25 Label Num +---------+---------+---------+---------+---------+ Pr (C9b) 15 òø Pv (D1a) 24 òôòø Pr (C9b) 17 òúó Pv (D1a) 26 ò÷ó Pr (C9b) 16 òûòüòòòòòòòòòø Pv (D1a) 25 ò÷óó Pr (C9b) 14 òòò÷ó Tc (A6) 11 òøùòòòø Tc (A6) 12 òôòøóó Tc (A6) 13 ò÷óóó Ap. (C70) 5 òøóóó Ap. (C70) 6 òôòüòòòòòòòòò÷ó Ap. (C70) 4 ò÷óùòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòø Ap. (C70) 7 òòò÷óó Gf (C21a) 28 òøóó Gf (C21a) 29 òôòòòòòøóó Gf (C21a) 27 ò÷óóó Sp (C1) 19 òøùòòòòòòòòò÷ó Sp (C1) 20 òúóó Par (C1) 21 òôòòòòò÷ó Par (C1) 23 òúó Sp (C1) 18 òúó Par (C1) 22 ò÷ó Am (C3) 2 òøó Am (C3) 3 òôòòòøó Am (C3) 1 ò÷ùòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòòò÷ Pd (C1c) 8 òûòøó Pd (C1c) 10 ò÷ùò÷ Pd (C1c) 9 òòò÷ P. ryu. (C9b) & P. var. (D1a) Tridacna spp. (A6) & Aiptasia spp. (C70) G. fas. (C21a) S. pis. & P. rug. (C1) A. mic. (C3) & P. dam. (C1c)

  16. RESULTS Photo-physiological responses to thermal stress • Symbionts from Acropora microphthalma and Pocillopora damicornis were the most affected while those from Platygyra ryukyuensis and Pavona varians were least affected. Zooxanthellae typing • The ITS2 types were as follows: • Tridacna spp. – A6; Aiptasia spp. – C70; Acropora microphthalma – C3; Pocillopora damicornis – C1c; Stylophora pistillata and Pachyseris rugosa – C1; Platygyra ryukyuensis – C9b; Pavona varians – D1a.

  17. CONCLUSIONS • The present study suggests that different ITS2 types of zooxanthellae exhibit different PSII responses to temperature stresses, and thus may partly explain differential bleaching susceptibilities among some cnidarian/zooxanthellae assemblages. • The order of stress tolerances were D1a (Pavona varians) & C9b (Platygyra ryukyuensis) > A6 (Tridacna spp.) & C70 (Aiptasia spp.) > C21a (Galaxea fascicularis) > C1 (Stylophora pistillata & Pachyseris rugosa) > C3 (Acropora microphthalma) & C1c (Pocillopora damicornis).

  18. FURTHER POTENTIAL INVESTIGATIONS • Carry out similar experiments on isolated symbionts from hosts found in other parts of the world like Heron Island and Mexico to see whether similar symbiont ITS2 types respond differently or not. • cDNA microarrays could be employed to explore upregulations and/or downregulation of genes in thermally tolerant and susceptible symbiont ITS2 types and attempt to investigate the molecular mechanism of thermal bleaching.

  19. ACKNOWLEDGEMENTS My sincere thanks go to: • Japanese Ministry of Education, Culture, Science and Technology for a scholarship • Tropical Biosphere Research center, University of the Ryukyus,Okinawa, Japan for logistic support. • Drs M. Hidaka, T. LaJeunesse, AC Baker and members of their labs.

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