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Slugs Hit the Big Time

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For the past several years, I have been exploring the world of sea slugs in the genus Elysia.  They are cool for any number of reasons, including their exploitation of the chloroplasts from their food algae (kleptoplasty).  I was very excited to see that one species recently made it into the journal Science, because of a weird, complicated relationship between the slug, the species of Bryopsis on which it feeds, and a bacterium in the alga that makes a toxic compound that ultimately protects the alga and the slug.


Here's the summary figure from the article (Zan et al. (2019) “A microbial factory for defensive kahalalides in a tripartite marine symbiosis.”  Science 364:eaaw6732; unfortunately behind a paywall)



The authors discovered a bacterium living within the species of Bryopsis algae upon which Elysia rufescens feeds. This bacterium is responsible for the production of a chemical compound called kahalalide F (KF).  The following observations are what make the story more interesting:

  1. The bacterium makes KF by stitching together amino acids using a biochemical pathway very different from that used by animals and plants.
  2. The bacterium, “Candidatus Endobryopsis kahalalidefaciens,”  has adapted to the comfortable life inside plant cells by getting rid of many of its genes, and can no longer live on its own.
  3. Although E. rufescens concentrates KF in its tissues to deter predators, it does not maintain the bacteria in its tissues.  This contrasts with the chloroplasts from Bryopsis, which a separated from the other cellular components and continue to photosynthesize in the slug.

There is a writeup on my page here: (It Takes Three to Tango).  If you have access, you can find the article at https://www.sciencemag.org/

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