Endosymbiosis between salamanders and algae

Researchers at the American Museum of Natural History have discovered an unlikely relationship between spotted salamanders (Ambystoma macultaum) and green algae (Oophila amblystomatis), which begins while the salamander is still in the embryonic stage.

Described as ‘endosymbiosis’ the algae have been observed growing within the salamanders egg. This process, which is the equivalent to plants growing within the womb, is visible to the naked eye and has puzzled scientists for hundreds of years.

In a recent study lead by John Burns, the researchers discovered that the stressed algae cells altered their way of converting food, suggesting they have adapted to support the baby salamander. In contrast, the salamander possesses several genes that would prevent an immune response, suggesting that the salamander benefits from the algae being there and has thus adapted to host the encroaching algae cells. Although work is ongoing, it is believed that the algae benefit from having access to more nitrogen, allowing it to grow denser than in the surrounding water. This nitrogen is then converted to oxygen which of course benefits the growing salamander.

One of the strangest puzzles of this phenomena is understanding how the algae made it into the egg in the first place. To figure this out, the researchers put some of the eggs under a microscope where they discovered the algae cells managed to develop, not just within the egg cells, but within the cells of the salamander itself. This is a process that is common within corals and some clams but is extremely rare amongst vertebrates.

By dividing the cells into four separate groups (salamander cells with algae, salamander cells without algae, algae cells in freshwater and algae cells inside the salamander egg) and counting how many types of RNA were in each cell, the researchers began to uncover more about the relationship. For example, the algae cells, after entering the salamander cells, turn off the genes associated with importing inorganic nutrients because they do not require them in such a nutrient-rich environment.

Researcher, Eunsoo Kim told AMNH Life Series: “We are learning that these two fundamentally different cells are changing each other really dramatically and this change may be relevant for other symbiotic systems including human and parasitic relationships.”

We have long understood that humans are covered in and filled with tiny, microscopic creatures which have a huge impact on our physical health, but could these have influenced our entire course of evolution? By better understanding the relationship between algae and the spotted salamander, we may one day better understand the impact of tiny micro-organisms on the entire human race.

Spotted salamander (Ambystoma maculatum)

The full research paper can be found at: https://elifesciences.org/articles/22054