The coral holobiont 10/17/ Holosymbiont 2.Emerging diseases 3.Holobiome/Holobiont

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1 The coral holobiont Overall model that corals exist in a multipartite symbiosis with both endosymbiotic dinoflagellate and resident microbiota (bacteria and archaea) Ainsworth et al 2010 Ainsworth et al Holosymbiont 2.Emerging diseases 3.Holobiome/Holobiont Although symbiotic corals are distributed over the entire photic zone, where they are exposed to a depth mediated light gradient spanning several orders of magnitude, most individual coral species have limited vertical distributions along this gradient. Physical and biological factors affecting the host? Predation by fishes? Growth forms survive waves, capture light. Clade/Type D1 Environment selection by algae? Specialized associations? Tested with recripocal transplants Clade/Type D1 Clade/Type C1c Clade/Type C1c Transplants all died. Not enough light/food. Many dead loose colonies 1

2 Holosymbiont idea that the physiological properties of a coral colony represent the emergent properties of the coral animal and the dinoflagellate symbionts. Clade/Type D1 A few lived but did not switch their symbionts some capacity for acclimation Nutrition Bleaching Light adaptation/zonation So how does this work? How/why does specificity arise? Clade/Type C1c Establishment of symbiosis (Horizontal transmission) Early = 30 minutes after innoculation Late = 6 days after innoculation CassKB8 (A1), Cassiopeia EL1 (A3), Cassiopeia Mf1.05b (B1), M. faveolata successful symbioses depend mainly on the symbionts ability to enter the host in a stealth manner rather than a more active response from the coral host. Voolstra et al The host transcriptome remains unaltered during the establishment of coral algal symbioses. Mol Ecol 18: Possibilities 1. Competent symbionts sneak in host doesn t notice 2. Competent symbionts are able suppress host response post transcriptional processes prevent phagosome maturation. 3. Response to symbionts is spatially restricted and hard to detect 4. Used arrays. Few genes, perhaps dominated by housekeeping genes 5. Missed window (Voolstra 30 min, 6 d post infection, Schnitzler 48 h post inf.) Normal cell defense Cell engulfs particle and creates a membrane around to create an internal vescicle called a phagosome. In the immune system, phagocytes have surface receptors to recognize invaders. The phagosome merges with lysosomes in the cell. Enzymes and peroxides produced by the lysosome digest the pathogen. Some symbionts and pathogens prevent maturation of the phagosome. 2

3 1. N 2 fixation mainly morning and evening in deeper colonies 2. Fixed nitrogen preferentially used by symbionts 3. Colonies with cyanobacteria have increased heterotrophy Lesser et a.l 2007 Marine Ecology Lesser et a.l 2007 Marine Ecology Coral Reefs 2005 Endolithic algae (Australian museum) Endolithic algal community at v. low abundance in healthy tissue of tabular acroporids. Significant agents of bioerosion 12 day period 3

4 Coral Diseases Global coral disease database NOAA CORIS disease page What is disease? Any impairment of an organisms vital functions or systems including interruption, cessation, proliferation, or other malfunction. Non infectious diseases Can be caused by poor nutrition, genetic mutations, exposure to conditions outside the normally tolerated ranges, Infectious diseases Can be caused by macroparasites (e.g., nematodes, mites and copepods) Or microparasites (e.g., bacteria, fungi, or protozoa) Photos by A. Bruckner, on CORIS disease webpage. From left, dark spots, black band, bleaching Originally in Dichocoenia stokesi. Spread rapidly along Keys Eventually in 16 coral spp. Isolated a gram negative Sphingomonas like bacteria Able to reproduce infection. Seasonal re occurrences (June Oct) have been noted. White plague Type II The disease modeled by Yacob and Mumby Richardson et al Nature Richardson et al Nature White Pox or Acroporid serratiosis (APS) Serratia marcescens opportunistic human pathogen present in untreated sewage Isolated from infected corals. Also non host corals and predatory snails thought to serve as reservoirs A reverse zoonosis 4

5 Rosenberg and Falkovitz Annu Rev Microbiol 58: Oculina patagonica is a facultatively symbiotic (also grows in dark caves) coral common in the Mediterranean Sea. Bleaches annually in Spring/Summer. Recovers in Fall. Vibrio shiloi, O. patagonica and Koch s Postulates 1. Bacteria (Vibrio shiloi) isolated from 28 bleached corals but not from 24 unbleached corals. 2. Obtained in bacteria in pure culture. 3. V. shiloi at elevated temperatures caused bleaching of healthy corals. No bleaching without the bacteria or with antibiotic co treatment. 4. Re isolated bacteria from infected corals Proposed that (1) bacteria enter a viable but non culturable state as they differentiate and become virulent in coral tissue (2) fireworms act as a winter reservoir for the bacteria (bacteria don t survive in coral below 20C and hadn t been found outside the coral). Using FISH, found no evidence for Vibrio association with bleached tissues. Did see changes in endolithic community (shift from cyanobacteria to green algae. Could detect bacteria within experimentally infected corals (provided by Rosenberg) but more recent studies showed resistance to bacterially induced bleaching. Role of microbial associations in coral bleaching remains controversial Rosenberg and Falkovitz Annu Rev Microbiol 58: Rosenberg et al ISME J 3: From Ainsworth et al (p. 234) Why Koch s postulates don t address the full complexity 1. Most marine microbes require complex conditions. Limited ability to culture. 2. Interdependent assemblages (e.g., BB consortium) 3. Microbes may have specific relationships with host, affected by host factors. 4. Coral disease signs are vague. Degraded tissues rapidly colonized (e.g., overgrowing cyano s and endolithic algae) 5. Phylogenetic markers don t tell us much about metabolic capability. Black band disease First reported ~1973 Band contains a microbial consortium Band primarily composed of filamentous cyanobacteria sulfide oxidizing bacteria, sulfide reducing bacteria heterotrophic bacteria Not highly infectious Associated with other stressors, high temp, sedimentation etc. 5

6 Aspergillosis, sea fan disease Bruno et al Ecological Monographs Host Pathogen Disease Environment Pathogen Host Susceptibility Disease Fungus that also affects crops and sometimes humans (lung). Big outbreak in Caribbean ~ Cause unknown (dust?). Perhaps spread through gastropod predators. Apparent evolved (selected for) host resistance. After Snieszko 1973 And Tlusty 2007 Environment Hologenome theory of evolution The object of natural selection is the holobiont (Rosenberg et al Nature Reviews Microbiol. Rosenberg et al The hologenome theory of evolution contains Lamarckian aspects within a Darwinian framework. Environ Microbiol. 6