Bacteria Act as Aphrodisiac for the Closest Relatives of Animals

Video: Arielle Woznica/Nicole King lab, UC Berkeley

Though ubiquitous in the oceans, choanoflagellates are relatively mysterious — one reason that King has focused on them for more than a decade. In 2008, she was part of a team that sequenced the first genome of a choanoflagellate, Monosiga brevicollis, and in 2012 her lab discovered the bacteria that trigger multicellularity.

Mating, however, was a mystery — even whether choanos engaged in sexual reproduction — until her team discovered in 2013 that starvation could trigger mating, although only a small percentage of cells would mate. The new study shows that Vibriobacteria elicit a much more rapid response, with large percentages of cells mating within hours.

“Choanoflagellates have a lot of flexibility in their life history. They can go on and on being asexual, but now we’ve found that they can also be sexual, and that the switch to sexuality is induced by a bacterial cue within an hour after exposure,” says King.

Bacterial aphrodisiacs

The new discovery suggests that other creatures, including some that have been difficult to study in the lab because they fail to mate, may need a little bacterial aphrodisiac to get it on.

A different bacterium induces the development of multicellular rosettes, which arise through multiple divisions of a single founding cell. Clues to the roots of animal evolution may lie in these choanoflagellate rosettes, shown here with tubulin protein labeled in green and actin labeled in magenta.

(Image courtesy of Arielle Woznica)

“One possibility is that these animals need particular cues from environmental bacteria that are not being provided in the lab,” she said.

After UC Berkeley graduate student Arielle Woznica discovered that these bacteria initiated swarming, they collaborated with Clardy’s lab to track down the trigger: a protein constantly secreted by the bacteria, which they dubbed EroS.

They showed that EroS is a chondroitinase, an enzyme that degrades a specific type of sulfated molecule found in the extracellular matrix of S. rosetta that was previously thought to be exclusive to animals. They also found that if this enzymatic function was inhibited, swarming did not occur, and that chondroitinases from other aquatic bacteria reproduced the aphrodisiacal effects. As the teams investigate how EroS works, they’re continuing to explore the interactions between bacteria and choanoflagellates.

As for implications for animals like humans and their bacterial partners, the so-called microbiome, King said that “we hope that by studying choanos, which are really simple, that we can identify key molecules and then go into the more complex environment of the gut microbiome, for instance, and see whether some of these molecules matter in that context as well.”

“I think by demonstrating a new type of bacteria-induced behavior, we may inspire others to look in the systems they study and see if they might have missed that bacteria play a role there as well,” said co-first author Joseph Gerdt, a postdoctoral researcher at Harvard Medical School.

This work was funded by the National Institutes of Health (grant GM099533). Ryan Hulett of UC Berkeley is also a co-author of the paper.

ontacts and sources:
Robert Sanders
University of California Berkeley

Citation: Mating in the closest living relatives of animals is induced by a bacterial chondroitinase (Cell)