A proposed new coral disease aetiology.


My 28 October 2016 seminar at the School of Animal and Veterinary Science of the University of Adelaide, presented preliminary research proposing that the Folliculinid protists and Vibrio bacteria may have a comensalistic relationship. I propose that association produces what I call a: Protist/Vibrio Coral Disease Syndrome (PVCDS).

Basically, folliculinid lorica are chitin and vibrio are attracted to chitin. I propose that this association may produce some coral diseases, in particular so-called “black-Band” disease. In the past both folliculinids and vibrio have been individually associated with coral disease. To date the two have not been seen as acting together to produce coral disease. I have carried out Scanning Electron Microscopy (SEM) which reveals vibrio colonising folliculinid lorica and cement (Plates 1-4).

I propose that folliculinids and vibrio together have a causative aetiology in producing “Black Band” coral disease. This involves a complex aetiology as follows:

  • Folliculinid lorica and cement are chitin,
  • Folliculinids colonise coral, covering hydroids preventing them from feeding, the hydroids die and provide dead tissue which are susceptible to infection by vibrio,
  • Vibrio have an established relationship with chitin, using it for a substrate, food, and protection from their predators. In utilizing chitin vibrio produce ammonium which repels nano-flagellates. Vibrio are therefore attracted to the folliculinid lorica and cement. (see plate 2.)
  • Nano-flagellates are the main predator of vibrio,
  • Next the folliculinids multiply and so do their associated exosymbiont vibrio,
  • Vibrio multiply and at an advanced stage, Quorum Sensing Autoinducers signal the vibrio to revert to a planktonic stage.
  • Vibrio “jump-ship” and infect other coral hydroids.
  • These infected coral hydroids provide a base for a rapidly expanding dark band of disease on coral,
  • Cascade Effect: Coral hydroids are a colonial organism, they respond to and react to each other, what happens to some may impact on many others. This may lead to a collapse of an entire colony of hydroids,

Is there a solution?

If my idea is correct there may also be a remedy – bacteriophages.

  • Bacteriophages are ubiquitous marine viruses that infect bacteria.
  • Bacteriophages are ubiquitous in our oceans, it is assumed that at any one time there are trillions of phages in our oceans.
  • Importantly they appear to be host specific, often to a single species, even a strain of a species.
  • Bacteriophages are easily cultured and it may be possible to “infect” coral disease areas with phages.

My research into PVCDS continued with a visit to Dr Tracy Ainsworth and her collegues at James Cook University in mid February 2017. Dr Ainsworth is a research fellow in the ARC Centre of Excellence for Coral Reef Studies. I inspected coral collections for folliculinids and visited sites.

Next steps in 2018 include:

  1. Collecting and describing folliculinids found on coral from various sites on the GBR and in Western Australia.
  2. Collecting and culturing vibrio associated with folliculinids
  3. Collecting “wild marine” vibrio on chitin chips
  4. DNA/RNA sequencing of vibrio associated with folliculinids and coral disease
  5. Setting up a series of small marine aquaria with healthy coral,then infecting with folliculinids, vibrio  and folliculinids plus vibrio, along with controls as per Koch’s Postulates.

SCANNING ELECTRON MICROSCOPE IMAGES.

FCGAND10 F coobowii

Plate 1: SEM of a Folliculinid  chitinous lorica and cement, specimen from Coobowie Aquatic Reserve South Australia. (JSD Adelaide Microscopy – Phillips XL 30 SEM – 2016)

vibrio-on-folliculinid-cement-picture1

Plate 2: SEM of the lorica in plate 1, and its cement, note “clusters of chitolytic vibrio on cement. (Adelaide Microscopy Philips XL 30 SEM)


PLATE 3: Carbon coated lorica with rosettes of vibrio on lorica surface (Plate 3 and 4 imaged 01/02/2017 on Quanta 450 SEM at Adelaide Microscopy Centre).

PLATE 4: High resolution SEM image of rosettes of vibrio on lorica surface.

This is this quorum sensing at work. Rosette formation is induced by signal molecules (autoinducers) secreted by the vibrio. This may be a protection mechanism as the rosettes produce cell adhesion proteins which can be switched off to release the vibrio to become planktonic. Also the rosettes may be concentrating the ammonium that is produced when vibrio lysis chitin, this ammonium attacks bacterivorous nanoflagellates which eat the vibrio.

Reference:

“Ammonia is a common toxic substance in polluted water bodies. So we tested the effects of different levels of ammonia on the grazing rate of the nanoflagellate. The results showed that the grazing rate was negatively affected by increasing levels of ammonia. When the concentration of ammonia was at 27.0 mg.Lx1 , the grazing rate of NF-WJ05 decreased by 45.3% as compared to the control”.Quote from “A heterotrophic nanoflagellate grazing on the toxic Cyanobacterium Microcystis aeruginosa”  Cui Yan, Jian-Hong Li*, Ju-Jiao Li, Jin Wang and Yong-Ping Weng Jiangsu Key Laboratory of Biodiversity and Biotechnology, Life Sciences College, Nanjing Normal University, Nanjing 210046, P. R. China.Ann. Limnol. – Int. J. Lim. 45 (2009) 23–28 Available online at:  EDP Sciences, 2009 www.limnology-journal.org DOI: 10.1051/limn/09004

PLATE 5: Large cyanobacterium caught gliding through its slime sheath, which it jets out of pores in its surface as shown below.

Diagrams from cronodon.com.


This is a first outline of research in progress at Adelaide University leading to publications in a peer reviewed journal as part of my PhD.