Berkeley scientists discover new species of algae Class In Mono Lake, multicellular colonies are formed and host a microbiome, providing new perspectives on the evolution of multicellular organisms.
The arsenic- and cyanide-laced saltwater of Mono Lake in the eastern Sierra Nevada is an extremely hostile environment. Except for abundant brine shrimp and black clouds of alkali flies, very few living things live there.
Now, researchers from University of California, Berkeley Scientists have discovered a new creature lurking in the shallow, salty waters of a lake that could tell scientists about the origin of animals more than 650 million years ago.
Discovery of algae
The organism is an alga, a microscopic, single-celled life form that can divide and develop into multicellular colonies in a manner similar to how animal embryos form. However, it is not a species of animal, but rather a member of a sister group to all animals. As the closest living relative of animals, algae are a crucial model for the leap from unicellular to multicellular life.
Surprisingly, this algae has its own microbiome, making it the first algae known to form a stable physical relationship with bacteria, rather than just eating them. Thus, it is one of the simplest organisms known to have a microbiome.
Algae: Bridging the Gap in Evolution
“Very little is known about algae, and there are interesting biological phenomena that we can only gain insight into if we understand their environment,” said Nicole King, a professor of molecular and cell biology at UC Berkeley and a Howard Hughes Medical Institute (HHMI) investigator who studies algae as a model for early life in ancient oceans.
Aquatic algae, which can usually only be seen through a microscope, are often overlooked by aquatic biologists, who instead focus on microscopic animals, photosynthetic algae, or bacteria. But their biology and lifestyle could provide insight into the creatures that existed in the oceans before animals evolved and that eventually gave rise to animals. This species in particular could shed light on the origin of the interactions between animals and bacteria that led to the emergence of the human microbiome.
“Animals evolved in oceans filled with bacteria,” King says. “If you think of the tree of life, all organisms alive today are related to each other through evolutionary time. So if we study organisms alive today, we can reconstruct what happened in the past.”
King and her colleagues at the University of California, Berkeley, described the organism—which they named Baroque Monsieur, After the Lake – In a research paper published in the journal MBIO.
A new species of organism called Barroeca monosierra has been discovered in Mono Lake. Colonies of these organisms are made up of many identical cells (cyan), each with flagella (green) that allow them to propel themselves through the water. This colony of canophagilines hosts its own microbiome (red), something never before seen in this organism. The extracellular matrix with which the bacteria interact is shown in white. Copyright: Davis Laundon and Pawel Burkhardt, SARS Center, Norway; Kent McDonald and Nicole King, UC Berkeley
Insights from an amazing discovery
Nearly a decade ago, Daniel Richer, then a graduate student at the University of California, Berkeley, returned from a hike in the eastern Sierra Nevada with a vial of Mono Lake water he had collected by chance along the way. Under a microscope, the water was teeming with algae. Aside from brine shrimp, alkali flies, and various species of nematodes, little else had been reported in the lake’s inhospitable waters.
“It was filled with these big, beautiful colonies of algae, I mean it was the largest we’ve ever seen,” King said.
Colonies of what appeared to be about 100 identical cells of the banded cells formed a hollow sphere that spun and spun as each individual cell kicked its flagella.
“One of the interesting things about these colonies is that they have a similar shape to a blastocyst — a hollow ball of cells that forms early in an animal’s development,” King said. “We wanted to learn more about them.”
At that time, however, the king was busy with Other types of chanoisAs you call them, the Mono Lake fish lay dormant in the fridge until some students woke up and colored them to look at their unusual, circular chromosomes. Surprisingly, there were also DNA Inside the hollow colony were cells that shouldn’t be there. After further investigation, graduate student Kylie Hack determined that they were bacteria.
Study of algae and bacteria
“The bacteria were a big surprise,” King said. “It was really interesting.”
Hack also discovered connective structures, called extracellular matrix, within the spherical colony secreted by the choanus. It was only then that it occurred to Hack and King that these might not be the remains of bacteria that the choanus feed on, but bacteria living and feeding on the things the colony secretes.
“No one has ever described algae with stable physical interactions with bacteria,” she said. “In our previous studies, we found that algae respond to small bacterial particles floating through the water, or [that] “The shoal fish were eating bacteria, but there was no instance where they were doing anything that could be a potential symbiosis. Or in this case, a microbiome.”
Future research and implications
King teamed up with Jill Banfield, a pioneer in biogenomics and a professor of environmental science, policy and management and earth and planetary sciences at UC Berkeley, to identify the types of bacteria present in the water and within the coral reefs. Biogenomics involves sequencing the DNA in an environmental sample to reconstruct the genomes of the organisms living there.
After Banfield’s lab identified the microbes in Mono Lake’s water, Hack created DNA probes to identify the microbes also found inside the corals. The bacterial populations weren’t identical, King said, so some bacteria clearly thrived better than others in the cavity of the oxygen-deprived coral colony. Hack decided that the bacteria weren’t there by chance; they were growing and dividing. They might be escaping the lake’s toxic environment, King speculated, or the corals might be cultivating the bacteria to eat.
Much of this is speculation, she admits. Future experiments should reveal how the bacteria interact with the algae. Previous work in her lab has already shown that bacteria act as aphrodisiacs to stimulate mating in algae, and that bacteria can encourage single-celled algae to aggregate into colonies.
For her, the Mono Lake dinoflagellates will become another model system for studying evolution, just like the dinoflagellates that live in saltwater pools on the Caribbean island of Curaçao—her main focus at the moment—and the dinoflagellates in Arctic and Antarctic pools. However, it may be difficult to obtain more samples from Mono Lake. On a recent visit, only six out of 100 samples contained these active microorganisms.
“I think there’s a lot to be done with the microbial life in Mono Lake, because it really supports everything else about the ecosystem,” King said. “I’m excited about B. Monocera “It’s a new model for studying interactions between eukaryotes and bacteria. I hope it tells us something about evolution. But even if it doesn’t, I think it’s a fascinating phenomenon.”
Reference: “A large group of colonizing algae from Lake Mono contains live bacteria” by K. H. Hake, P. T. West, K. McDonald, D. Laundon, J. Reyes-Rivera, A. Garcia De Las Bayonas, C. Feng, P. Burkhardt, D. J. Richter, J. F. Banfield, and N. King, August 14, 2024. MBIO.
DOI: 10.1128/mbio.01623-24
This work is supported by the Hughes Medical Institute and the National Science Foundation.
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