Fungus With Over Half a Million Clonal Cells Grew 20,000 Times Larger Than Their Ancestor in an Unmatched Cellular Evolution

Researchers at the Georgia Institute of Technology have taken on the task of understanding the evolution of multicellular life by initiating a groundbreaking long-term evolution experiment using a common fungus. Led by William Ratcliff, a team of scientists aims to evolve new types of multicellular organisms in the laboratory, starting from single-celled ancestors.

The study, titled "De Novo Evolution of Macroscopic Multicellularity" published in the journal Nature, seeks to shed light on the poorly understood transition from single-celled organisms to complex multicellular species that occurred millions of years ago and whose early forms have largely vanished due to extinction.

Unmatched Multicellular Evolution of 3,000 Generations

The study has provided insight into the evolution of multicellular organisms through the examination of a mutated brewer's yeast (Saccharomyces cerevisiae) known as 'snowflake' yeast, Science Alert reported.

Over thousands of generations of careful selection, the yeast underwent significant changes, forming large clusters containing over half a million clonal cells, a size 20,000 times larger than its ancestor. This study presents a remarkable example of sustained multicellular evolution.

The research aims to understand how single-celled organisms transitioned into complex multicellular forms with specialized tissues and coordinated activity, which occurred billions of years ago as shown in previous studies.

By observing the snowflake yeast, scientists can gain valuable insights into this evolutionary journey. After 3,000 generations of evolution, the yeast populations demonstrated remarkable transformations, progressing from gelatin-like substances to structures with the strength and toughness of wood.

The researchers identified a new physical mechanism behind the yeast's growth. The yeast cells evolved larger branches, reducing overall density; and these branches intertwined, forming a cluster with a gel-like consistency.

This new structure made the organism 10,000 times tougher than its single-celled ancestor. The yeast cells exhibited vine-like behavior, wrapping around each other and strengthening the entire structure.

These findings shed light on the evolutionary processes that facilitated the transition from single-celled organisms to multicellular life forms. The study demonstrates how a single-celled organism can evolve into a complex and integrated multicellular organism over thousands of generations of selection, offering valuable insights into the origins of multicellularity.

Oxygen's Role in Multicellular Evolution

The experiments on snowflake yeast have yielded another significant finding related to the role of oxygen in evolutionary progress. Science Alert previously reported that oxygen was scarce in the early history of Earth until a specific type of bacteria introduced it into the atmosphere billions of years ago, believed to have facilitated the emergence of multicellular life forms.

The evolution of snowflake yeast in the lab provides support for the idea that oxygen played a crucial role in shaping the first multicellular organisms on Earth.

The experiments revealed that only yeast populations that did not rely on oxygen for energy production were capable of evolving into larger sizes. In contrast, yeast clusters dependent on oxygen had to divide their resources among all cells, imposing an additional cost on growth.

These findings highlight the significance of oxygen levels in the evolution of multicellular organisms and their size. The ability to observe the evolution of early multicellular life forms over thousands of generations using the snowflake yeast provides an exciting opportunity to study various aspects, including evolutionary cell biology and the biophysical traits subject to natural selection.

Researchers, including William Ratcliff, said in a press release that they are excited about this model system and anticipate further discoveries in the future as they continue to monitor the behavior and evolution of this yeast species.