Mono Lake in the Eastern Sierra Nevada is known for its towering tufa formations, abundant brine shrimp and black clouds of alkali flies uniquely adapted to the salty, arsenic- and cyanide-laced water.
This species in particular could shed light on the origin of interactions between animals and bacteria that led to the human microbiome.
“Animals evolved in oceans that were filled with bacteria,” King said.
“It was just packed full of these big, beautiful colonies of choanoflagellates,” King said.
After Banfield’s lab identified the microbes in Mono Lake water, Hake created DNA probes to determine which ones were also inside the choanos.
Perhaps they were escaping the toxic environment of the lake, King mused, or maybe the choanos were farming the bacteria to eat them.
It might be a challenge to get more samples from Mono Lake, however.
“I think there’s a great deal more that needs to be done on the microbial life of Mono Lake, because it really underpins everything else about the ecosystem,” King said.
Towering tufa formations, an abundance of brine shrimp, and black clouds of alkali flies that are specially adapted to the salty, cyanide- and arsenic-laced water are the main attractions of Mono Lake in the Eastern Sierra Nevada.
Now, scientists from the University of California, Berkeley have discovered another strange animal hiding in the salty shallows of the lake. This discovery may provide insight into the evolution of animals over 650 million years ago.
The creature is a choanoflagellate, a microscopic single-celled organism that resembles animal embryos in its ability to divide and grow into multicellular colonies. It belongs to a sister group that includes all animals instead of being a specific kind of animal. And the choanoflagellate, the nearest living relative of animals, is an essential model for the transition from single-celled to multicellular life.
It is the first choanoflagellate known to form a stable physical relationship with bacteria rather than consuming them entirely, and this is due to its surprising ability to harbor its own microbiome. It’s among the simplest organisms known to have a microbiome as a result.
Nicole King, a Howard Hughes Medical Institute (HHMI) investigator and professor of molecular and cell biology at UC Berkeley, said, “Very little is known about choanoflagellates, and there are interesting biological phenomena that we can only gain insight into if we understand their ecology.” King uses choanoflagellate research as a model for early life that may have existed in ancient oceans.
Aquatic biologists mainly study macroscopic animals, photosynthetic algae, or bacteria; they rarely look at choanoflagellates, which are usually only visible under a microscope. Their biology and way of life, however, can shed light on organisms that once lived in the oceans before animals evolved and eventually gave rise to animals. The origin of the interactions between animals and bacteria that gave rise to the human microbiome may be clarified by looking specifically at this species.
King claimed, “Animals evolved in bacterially-rich oceans.”. All currently existing organisms are related to one another through evolutionary time, if you consider the tree of life. It is therefore possible to reconstruct historical events through the study of extant organisms. “.”.
The organism was named Barroeca monosierra after the lake by King and her colleagues at UC Berkeley, who published a paper on the subject in August. 14 in the mBio journal.
Lovely colony.
Daniel Richter, a graduate student at UC Berkeley at the time, returned from a climbing expedition in the Eastern Sierra Nevada almost ten years ago carrying a vial containing water from Mono Lake that he had haphazardly collected along the way. Choanoflagellates were living inside of it, visible under a microscope. A few other species of life have been reported to exist in the lake’s unfriendly waters, including brine shrimp, alkali flies, and different types of nematodes.
King remarked, “It was just full of these huge, gorgeous colonies of choanoflagellates.”. “They were the largest ones we had ever seen, really. “.
As each individual choanoflagellate cell kicked its flagella, the colonies of what appeared to be almost 100 identical cells formed a hollow sphere that swirled and beat.
According to King, “one of the interesting things about them is that these colonies have a shape that’s similar to the blastula—a hollow ball of cells that forms early in animal development.”. “We desired to understand it better. ****.
However, the Mono Lake choanos languished in the freezer until some students revived them and stained them to examine their peculiar, doughnut-shaped chromosomes because King was preoccupied at the time with other species of choanos, as she calls them. Unexpectedly, DNA was also found inside the hollow colony where no cells should have been. These turned out to be bacteria, according to research done by graduate student Kayley Hake.
“The bacteria came as a major shock. That was really intriguing, King remarked.
Additionally, Hake found that the choanos secreted connective structures inside the spherical colony, which are referred to as extracellular matrix.
Hake and King didn’t realize until later that these might not be bacteria that the choanos had eaten, but rather bacteria that were grazing on materials secreted by the colony.
She said, “No one had ever described a choanoflagellate with a stable physical interaction with bacteria.”. “In our earlier research, we discovered that choanos either ate the bacteria or responded to tiny bacterial molecules floating through the water; however, we did not find any instances in which they appeared to be engaging in any possible symbiotic activity. or, as it applies here, a microbiome. “.”.
To find out which bacterial species were in the water and inside the choanos, King collaborated with Jill Banfield, a pioneer in metagenomics and a professor of Earth and planetary science at UC Berkeley as well as environmental science, policy, and management. In order to reconstruct the genomes of the organisms that inhabit an environment, a process known as metagenomics entails sequencing every piece of DNA found in the sample.
Once the microbes in the Mono Lake water were identified by Banfield’s lab, Hake made DNA probes to find out which ones were also inside the choanos. According to King, there were differences in the bacterial populations, indicating that certain bacteria are able to thrive in the oxygen-deprived lumen of the choanoflagellate colony more than others. Hake concluded that their presence was not coincidental; rather, they were proliferating and segmenting. King wondered if the choanos were farming the bacteria to eat them, or if they were just trying to get away from the toxic lake environment.
As she admits, a lot of this is conjecture. Subsequent investigations ought to reveal the manner in which the bacteria and choanoflagellates communicate. Past research in her lab has already demonstrated that bacteria can induce single-celled choanos to assemble into colonies and that they function as an aphrodisiac to promote mating in choanoflagellates.
She plans to use the Mono Lake choanoflagellate, as well as the choanos found in splash pools on the Caribbean island of Curaçao—her current primary focus—as another model system to study evolution. Obtaining additional samples from Mono Lake may prove to be difficult, though. Of the 100 samples examined during a recent visit, only six had these active microbes.
According to King, “I think a great deal more work needs to be done on Mono Lake’s microbial life, because it really underpins everything else about the ecosystem.”. About B, I’m thrilled. monosierra as a novel model to investigate bacterial-eukaryotic interactions. Additionally, I hope it sheds some light on evolution. Even so, I find it to be an interesting phenomenon. “. .
Postdoctoral fellows Josean Reyes-Rivera and Alain Garcia De Las Bayonas, electron microscopist Kent McDonald, former PhD student Patrick West, and Banfield, Hake, and Richter are among the UC Berkeley co-authors of the paper.
