The diet of the iguanas of the Galapagos islands is dependent on unique algae, native to the islands. But during El-Nino events, the algae die, as do 90% of the iguanas. Scientists from Israel, the US, Germany and Ecuador have found microbes in the gut of surviving iguanas that could save the species.

https://aabgu.org/saving-the-iguanas/

https://www.youtube.com/watch?v=jnb1I8OU4Io