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Did bacteria trigger multicellular life?

by CIFAR Nov 12 / 12

A new study suggests that bacteria may have played a key role in our evolutionary history.

A team of researchers led by Fellow Nicole King (UC Berkeley) in CIFAR’s Integrated Microbial Biodiversity program found that bacteria and the molecules they produce may have triggered some single-celled organisms to start forming colonies, leading to the evolution of multi-celled organisms into animals, including humans. The team’s findings were published in the first edition of the new open source journal eLIFE.

Salpingoeca-rosetta
Salpingoeca rosetta colonies.
IMAGE CREDIT: Mark J. Dayel

The team studied a particular kind of single-celled organism, found in both fresh and salt waters around the world, called a choanoflagellate, or choano. In evolutionary terms, choanos are considered one of the closest living relatives of animals. Learning more about these organisms provides insights into the biology of a common genetic ancestor to animals, and reveals how multicellular animals may have first evolved.

In the study, the researchers investigated why the choanos sometimes swim and live on their own, while at other times cluster in the shape of a rosetta to form a colony. By experimenting with the organisms in the lab, they found that the presence of a fat molecule, produced by a specific bacterium called Algoriphagus machipongonensis, stimulated the choanos to reproduce and form colonies.

Careful observation and curiosity led the team to make their unexpected discovery. While routinely using antibiotics to clear out bacteria from samples of choanos, the team noted that certain cocktails of antibiotics triggered colony formation, while others did nothing. Further investigation allowed the team to pinpoint which specific bacterium was shaping this rosetta phenomenon.

The next step for Dr. King and her team will be to investigate how the fat molecule causes colonization. Analyzing the genomes of both the choanoflagellate and bacterium promises to explain the nature of their interaction and a potential explanation of how single-celled organisms became the building blocks for multicellular life.