Photosynthetic Animals

December 16, 1998
From: Michael Rhodin

Dear Dr. Bill Rudman,
My name is Michael Rhodin and I am a freshman at Trinity College in Hartford CT. I am doing research on the possibility of introducing a working chloroplast into an animal cell to make it photosynthetic. I have looked at the sea slug Elysia chlorotica and seen that it eats a type of algae called Vaucheria litorea, and its cells incorporate the chloroplasts into the slug's cells. I have also found that there are several genes found in the Elysia chlorotica which match the genes of the Vaucheria litorea, genes which work in relation to the chloroplasts. I was wondering if it would be possible through recombinant DNA to remove these genes and insert them into another creature's cells such as a fish, invertebrate, or reptile. Then I was wondering if that organism ate the Vaucheria litorea, would it take up and maintain the chloroplasts? Has this been attempted? Do you think it could work? Thank you for your time, this really is a big help, and a matter of great interest to me. I am so glad that I have found your site.
Michael Rhodin

Rhodin, M., 1998 (Dec 16) Photosynthetic Animals. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Michael,
I am not an expert in plastid physiology so I have sent copies of your message to a few colleagues who hopefully are more able to answer your question intelligently.

There are however a number of general points.
You say there are a number of genes in the Elysia which match the genes in the Vaucheria it feeds on. The obvious question to ask is how did you ensure that the Vaucheria-like genes were not contaminants from its food?

The other point is what got me interested in these symbioses in the first place, and that is the morphological adaptations that the "host" has undergone to become an efficient plastid or zooxanthellae "farmer". All these animals are related to animals which don't have symbiotic relationships and we can see how in certain phylogenetic lines of animals species have modified their anatomy, (finely branched gut, branches into the epithelial layer, flattened cerata, transparent bodies etc) all to better enable them to keep their plant tissues in an optimum environment for photosynthesising. A good example is shown in the aeolid genus Phyllodesmium where in one genus we can see major morphological changes which are correlated with the varying ability between species to grow zooxanthellae in their bodies (Rudman, 1991 - see references at top of page).

All things being equal, if gene transfer is the key - and possible, - then I suspect the experiment would only work in animals that had by chance a morphology which would provide an hospitable "nursery" for plant tissue. For example, the skin of most vertebrates, I would think, would block out sunlight and so prevent photosynthesis.

If you have any photos of Elysia chlorotica either on or off its food, or some photos of the plastids, it would be nice to put them up on the Sea Slug Forum.

With luck, one of the people I sent copies of your message to, will reply.
Best wishes,
Bill Rudman.

Rudman, W.B., 1998 (Dec 16). Comment on Photosynthetic Animals by Michael Rhodin. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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