July 27 (UPI) -- New analysis of common freshwater bacteria suggests some symbiotic relationships are marred by coercion -- more hostage situation than free exchange.
Polynucleobacter is a genus of freshwater bacteria whose species are typically found living inside euplotid ciliates, a group of single-celled protozoa.
"Most people think symbiosis means there is an evolution toward harmony, a perfect balance of the two partners," Vittorio Boscaro, a biologist at the University of British Columbia, said in a news release. "But although the host needs the bacterium to survive, the bacterium doesn't gain any advantage in this relationship."
Researchers found protozoa snatch up bacteria and host them them for a finite period of time before discarding the bacterium and finding a fresh replacement.
"They're being replaced, just like you change your clothes," said Patrick Keeling, a microbiologist at UBC. "You take advantage of your symbiont until it's no longer useful, and then you get a new one."
When Boscaro and his colleagues sequenced the genome of bacteria living inside euplotes, they found captured bacteria alter their genes haphazardly. They don't evolve to adapt inside the protozoan host; instead, they become genetically corrupted.
Simply put, the bacteria are in an unhealthy relationship. And they don't appear to have the power to leave.
"I like to think of the relationship being more like death row than cooperation -- sure the symbiont is kept safe and well-fed in the short term, but ultimately it's not a good place to be," said Keeling.
The researchers detailed the bacteria-protozoa relationship in a paper published this week in the journal Nature Ecology and Evolution.