Scientists at UC Berkeley have made a surprising discovery about choanoflagellate mating patterns that may help explain some aspects of early evolutionary biology.
In the paper, published last week in the journal Cell, the researchers explain that Choanoflagellates (a.k.a. choanos) “eavesdrop” on bacteria to make sense of their environment and determine whether to develop into multicellular colonies. This is the first known example of bacteria triggering mating in a eukaryote and may reveal how multicellular organisms evolved from unicellular ones.
"Bacteria are very good at integrating a lot of information about the environment, as different species of bacteria have different nutrient requirements. Choanos may be using bacteria as a proxy for environmental conditions, or live indicators for when it’s time to get ready for good or bad times," explains Nicole King, a professor of molecular and cell biology at UC Berkeley and Howard Hughes Medical Institute investigator.
Prior to this, King had been studying choanoflagellates for many years. In 2008 she was on the team that first sequenced their genome and in 2012 her lab discovered the bacteria that trigger multicellularity. In 2013 she discovered that starvation could trigger mating, though only a small percentage of cells would mate. This discovery pulls the pieces of the puzzle together to explain how addition of bacteria elicits a much more rapid response with large percentages of cells mating within hours.
The team named the protein that the bacteria secrete to initiate swarming EroS. EroS is a chondroitinase, an enzyme that degrades a specific molecule found in the extracellular matrix of the choanoflagellate S. rosetta, and was previously thought to be exclusive to animals.
Aside from its evolutionary implications, this research could help scientists studying other organisms with unusual mating patterns. It’s possible that adding the right bacteria could induce reproduction in their research organisms. The researchers also believe this may have implications for the human microbiome; using choanoflagellates as a model may help identify key molecules involved in cellular interaction between humans and bacteria.
Image: A mating swarm of the marine choanoflagellate S. rosetta, triggered by the bacterium V. fischeri.Tubulin is labeled gold, highlighting the cell body and flagellum, while the protein actin is labeled blue, showing off the organism's distinctive collar. Image curtesy of Arielle Woznica and Nicole King, UC Berkeley.