Microscopic Creature Found in Mono Lake Offers Insight into Early Animal Evolution

In the briny depths of California's Mono Lake, researchers have uncovered a microscopic wonder that could shed light on the origins of animal life. University of California, Berkeley, scientists have identified a new species of choanoflagellate—a microscopic, single-celled organism that is believed to be the closest living relative to all animals. This discovery, made in the unique environment of Mono Lake, offers a glimpse into the evolutionary transition from single-celled to multicellular life.

The Discovery: A New Species Revealed

Mono Lake, renowned for its towering tufa formations and its unique, saline ecosystem, has recently become the site of an exciting biological discovery. Researchers from UC Berkeley have documented a choanoflagellate species, now named Barroeca monosierra, in the lake's extreme conditions. This species is particularly noteworthy for its ability to form multicellular colonies and establish a stable relationship with bacteria, a phenomenon previously undocumented in choanoflagellates.

Barroeca monosierra is a fascinating example of a choanoflagellate forming colonies that resemble the blastula stage in early animal development. These spherical colonies are composed of numerous identical cells, each equipped with flagella that help propel them through the water. Unlike other choanoflagellates, Barroeca monosierra hosts its own microbiome, a community of microorganisms that live in a symbiotic relationship with the choanoflagellates.

Significance of the Microbiome Discovery

Nicole King, a UC Berkeley professor of molecular and cell biology and a Howard Hughes Medical Institute (HHMI) investigator, emphasizes the importance of this discovery. "Very little is known about choanoflagellates, and understanding their ecology is crucial for gaining insights into early life forms," she explains. This new species not only provides a model for studying the evolution of multicellular life but also represents one of the simplest organisms known to harbor a microbiome.

The microbiome of Barroeca monosierra challenges previous assumptions about choanoflagellates. Traditionally, these organisms were thought to only consume bacteria, but the new findings suggest a more complex interaction. The choanoflagellates are now known to support a stable community of bacteria, indicating a potential mutualistic relationship rather than a purely predatory one.

The Research Process

The discovery began nearly a decade ago when UC Berkeley graduate student Daniel Richter collected a sample of Mono Lake water during a climbing trip. Under the microscope, Richter and his colleagues observed colonies of choanoflagellates unlike any they had seen before. These colonies, consisting of up to 100 cells, formed a hollow sphere that spun as the cells' flagella propelled them through the water.

Further investigation revealed that these colonies contained bacteria within their interior, where no cells were expected to be. Graduate student Kayley Hake's research identified these bacteria as integral to the colony's structure, leading to the hypothesis that the choanoflagellates might be engaging in a form of symbiosis with the bacteria.

Insights and Future Directions

The findings, published in the journal mBio, represent a significant advancement in our understanding of choanoflagellate biology. By identifying the bacteria present in both the water and inside the choanoflagellates, researchers have uncovered a new aspect of these organisms' lives. The bacteria were found to thrive in the choanoflagellate's oxygen-starved environment, suggesting that they might be benefiting from this unique habitat.

Nicole King and Jill Banfield, a pioneer in metagenomics, collaborated to sequence the DNA of these microorganisms. Their work revealed that while some bacteria are better suited to the choanoflagellates' environment, others struggle to survive. This discovery opens new avenues for exploring how microorganisms and their hosts interact and evolve.

Implications for Evolutionary Biology

The study of Barroeca monosierra could provide crucial insights into the early evolutionary stages of animal life. As King notes, "Animals evolved in oceans teeming with bacteria. By studying modern organisms, we can reconstruct what happened in the past." This research not only enhances our understanding of choanoflagellates but also contributes to broader discussions about the origins of complex life forms.

The discovery of a choanoflagellate with a microbiome highlights the intricate relationships between early life forms and their microbial environments. This model system offers a unique opportunity to study these interactions and their implications for the evolution of multicellular organisms.

Challenges and Future Research

Despite the excitement surrounding this discovery, obtaining further samples from Mono Lake presents challenges. During a recent field visit, researchers found that only a small fraction of their samples contained the choanoflagellates. Nevertheless, King and her team are eager to continue their research, aiming to uncover more about the microbial life of Mono Lake and its implications for understanding early evolutionary processes.

In summary, the discovery of Barroeca monosierra in Mono Lake provides a valuable window into the past and the evolutionary journey from single-celled to multicellular life. As researchers continue to explore the microbiome of this unique choanoflagellate, they hope to uncover more about the origins of animal life and the complex interactions between early organisms and their microbial companions.

Keywords: choanoflagellates, Barroeca monosierra, Mono Lake, microbiome, early animal evolution, single-celled organisms, multicellular colonies, microbial interactions, UC Berkeley research, Nicole King, evolutionary biology