The effects of temperature and dark treatments on community dynamics of Endozoicomonas in corals

Coral associated bacteria are critical to the health and function of a coral holobiont, and often form stable homeostasis associations with their host. Changes in coral associated bacterial community may be regarded as an indicator to reflect the health of coral holobionts. Endozoicomonas, a recently identified bacterial genus, is commonly detected in corals, sponges, and other reef invertebrates. These bacteria have attracted attention on their putative functional roles in coral health. This dissertation includes (1) an introduction to bacterial community and coral-associated Endozoicomonas, (2) the variation in bacterial communities under both heat and cold stress between summer and winter, (3) a newly designed Endozoicomonas primer for detecting the distribution and diversity of coral-associated Endozoicomonas, and (4) changes in Endozoicomonas in darkness-mediated coral bleaching, and finally (5) followed by a general discussion. The result showed that the relative abundance of Endozoicomonas is sensitive to temperature, but not associated with the abundance of Symbiodinium. Their relative abundance decreased under both cold or heat stress, but maintained stable when coral bleaching induced by dark treatment. Although the relative abundance of Endozoicomonas was higher in coral than those in seawater, their diversity was higher in seawater samples than those in coral samples. In addition, the temporal shift of the most dominant Endozoicomonas species in coral was first reported in this study. Furthermore, we designed a Endozoicomonas-specific primer, which has high specificity and sensitivity to detect the communities of Endozoicomonas in coral. In the future, the sequence of primer is able to be used as a Endozoicomonas-specific probe for in situ hybridization to detect the location of Endozoicomonas inside their animal hosts. Based on our findings, we inferred that there were positive interactions between corals and Endozoicomonas, and their relationship should be highly flexible.Abstract of the Dissertation i Table of Content iii List of Figures v List of Tables viii Chapter 1. General introduction 1 1.1. Importance of coral reef ecosystem and coral holobiont 1 1.2. Bacteria in coral holobiont 2 1.3. Coral microbes under stress 4 1.4. Endozoicomonas 5 1.5. Motivations 13 1.6. Aims and outlines of this dissertation 14 1.7. Tables and figures 16 Chapter 2. Dynamics of coral-associated bacterial communities acclimated to temperature stress based on recent thermal history 22 2.1. Abstract 22 2.2. Motivation 23 2.3. Material and methods 25 2.4. Results 30 2.5. Discussion 35 2.6. Conclusions 40 2.7. Tables and figures 41 Chapter 3. A newly designed primer revealed high phylogenetic diversity of Endozoicomonas in coral reefs 52 3.1. Abstract 52 3.2. Motivation 53 3.3. Materials and methods 55 3.4. Result 64 3.5. Discussion 72 3.6. Conclusion 78 3.7. Tables and figures 79 Chapter 4. Dynamics and high abundance of Endozoicomonas in coral bleaching by darkness 95 4.1. Abstract 95 4.2. Motivation 96 4.3. Material and methods 98 4.4. Result 103 4.5. Discussion 108 4.6. Conclusion 114 4.7. Tables and figures 115 Chapter 5. Conclusion and general discussion 128 5.1 The coral associated Endozoicomonas communities are sensitive to temperature 128 5.2 The diverse and divergent role of Endozoicomonas in coral 128 Reference 131 Appendix 149 Appendix figures 149 Appendix tables 157 Curriculum Vitae 16