We study the biochemistry of cell-cell signals that maintain a
stable symbiosis between intracellular algae (zooxanthellae) and
their marine invertebrate hosts. Coral bleaching is one event that
is evidence of disruption to coral symbioses.
We have isolated two signalling molecules from homogenized tissue
of the scleractinian coral, Plesiastrea versipora that contains
Symbiodinium algae.
One molecule, host release factor (HRF), stimulates the release
of photosynthate from isolated algae and also reduces synthesis
of algal starch and triglycerides suggesting that it acts to divert
carbon from further algal metabolism to the host. It is a small
molecule (Mr of 500-1,000) which has a high absorbance at 215 nm
suggesting that it is probably a peptide. It also stimulates photosynthate
release from the algae of several other symbioses including zoanthids,
anemones and two other corals, as well as cultured algae from a
jellyfish.
The second signalling molecule, photosynthesis inhibiting factor
(PIF), partially inhibits photosynthetic carbon fixation in several
symbiotic algae but not those from anemone or jellyfish. It is also
a small molecule (Mr of 500-1,000) with a high absorbance at 215
nm, suggesting that it too is probably a peptide. We believe that
these molecules play important roles in controlling algal carbon
metabolism thus enabling the coral host to receive photosynthate
for its own nutrition, and also regulating the numbers of intracellular
algae to maintain a steady state population.
We are also studying the effects of pollutants on sessile marine
organisms and have developed assays for the early detection of pollution
damage in P. versipora. This research will help to prevent irreversible
damage to marine organisms in a variety of habitats and also help
to devise better management strategies of coral reefs.
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