Researchers have been looking into the greenish embryos of the spotted salamander (Ambystoma maculatum) for decades.1 This green colour is caused by the green alga Oophila amblystomatis, with whom the salamanders have a symbiotic relationship. Until recently they were thought to only occur outside the embryo, in its surrounding jelly sac.

The researchers found that these algae are often found inside cells throughout the spotted salamander’s body.2

The salamanders even appear to be using the algae to breathe. The intracellular algae also show signs of directly providing its photosynthetic products (oxygen and carbohydrates) to the salamanders. The cells with algae in them also appeared to have several mitochondria (the cell’s powerhouse) surrounding each alga. The mitochondria might be there to take advantage of the oxygen and carbohydrate generated by algal photosynthesis to provide energy for the salamander.

Only invertebrates, such as corals and some sea slugs (nudibranchs), have ever been found with such a close symbiotic relationship with a photosynthetic organism. Other sea slugs (sacoglossans) have even been found to use chloroplasts from algae they’ve eaten.3 Nobody thought algae could live inside vertebrate cells because vertebrates have an adaptive immune system.4 This system tells the difference between body cells and foreign cells, and it then destroys the cells it doesn’t recognize as ‘self’. But the algae still survive and thrive in the salamander cells….

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