Study finds four-way symbiosis in cicadas

http://www.eurekalert.org/pub_releases/2014-08/tuom-uom082114.php

PUBLIC RELEASE DATE: 28-Aug-2014

Contact: John McCutcheon
The University of Montana
University of Montana cicada study discovers 2 genomes that function as 1

MISSOULA, Mont. – Two is company, three is a crowd. But in the case of the cicada, that's a good thing.

Until a recent discovery by a University of Montana research lab, it was thought that cicadas had a symbiotic relationship with two important bacteria that live within the cells of its body. Since the insect eats a simple diet consisting solely of plant sap, it relies on these bacteria to produce the nutrients it needs for survival.

In exchange, those two bacteria, Hodgkinia and Sulcia, live comfortably inside the cicada. Since all three divvy up the nutritional roles, each member of the symbiosis is completely dependent on the others for survival.

So, where does this third-wheel bacterium come into play? That is exactly what UM microbiologist John McCutcheon and his team of colleagues stumbled upon once they started delving deeper into the genome sequence of the essential bacteria. Instead of two bacterial symbionts, they actually identified three. Sulcia was predictably still there, but they found two different kinds of Hodgkinia. What previously was thought to be a tripartite, or a three-way symbiosis, is now proven to actually be a four-way symbiosis.

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Because they only are complete when they operate as a team, they are reliant on each other just as the Sulcia, and ultimately the cicada, is reliant on their contributions to the symbiotic ecosystem.

"This is an obligate symbiosis – all of the organisms in there need each other," McCutcheon said. "We've shown that what was once a three-way symbiosis is now a four-way symbiosis."

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Hodgkinia's development closely parallels that of a path of some organelles. Essentially, organelles are to cells what an organ is to the human body. Mitochondria of our own cells are organelles, and like Hodgkinia, are derived from symbiotic bacteria.

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