from the just-so-long-as-it-didn't-come-from-a-black-lagoon dept.
Arthur T Knackerbracket has processed the following story:
The salty, arsenic- and cyanide-laced waters of the Eastern Sierra Nevada’s Mono Lake is an extremely hostile environment. Aside from the abundant brine shrimp and black clouds of alkali flies, very few organisms live there.
Now, researchers from the University of California, Berkeley have discovered a new creature lurking in the lake’s briny shallows — one that could tell scientists about the origin of animals more than 650 million years ago.
The organism is a choanoflagellate, a microscopic, single-celled form of life that can divide and develop into multicellular colonies in a way that’s similar to how animal embryos form. It’s not a type of animal, however, but a member of a sister group to all animals. As animals’ closest living relative, the choanoflagellate is a crucial model for the leap from one-celled to multicellular life.
Surprisingly, it harbors its own microbiome, making it the first choanoflagellate known to establish a stable physical relationship with bacteria, instead of solely eating them. As such, it’s one of the simplest organisms known to have a microbiome.
“Very little is known about choanoflagellates, and there are interesting biological phenomena that we can only gain insight into if we understand their ecology,” said Nicole King, a UC Berkeley professor of molecular and cell biology and a Howard Hughes Medical Institute (HHMI) investigator who studies choanoflagellates as a model for what early life was like in ancient oceans.
Typically visible only through a microscope, choanoflagellates are often ignored by aquatic biologists, who instead focus on macroscopic animals, photosynthetic algae, or bacteria. But their biology and lifestyle can give insight into 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 interactions between animals and bacteria that led to the human microbiome.
“Animals evolved in oceans that were filled with bacteria,” King said. “If you think about the tree of life, all organisms that are alive now are related to each other through evolutionary time. So if we study organisms that are alive today, then we can reconstruct what happened in the past.”
King and her UC Berkeley colleagues described the organism — which they named Barroeca monosierra, after the lake — in a paper published in the journal mBio.
Nearly 10 years ago, then-UC Berkeley graduate student Daniel Richter came back from a climbing trip in the Eastern Sierra Nevada with a vial of Mono Lake water he’d casually collected along the way. Under the microscope, it was alive with choanoflagellates. Other than brine shrimp, alkali flies and various species of nematode, few other forms of life have been reported to live in the inhospitable waters of the lake.
[...] At the time, however, King was occupied with other species of choanos, as she calls them, so the Mono Lake choanos languished in the freezer until some students revived and stained them to look at their unusual, doughnut-shaped chromosomes. Surprisingly, there was also DNA inside the hollow colony where there should have been no cells. After further investigation, graduate student Kayley Hake determined that they were bacteria.
“The bacteria were a huge surprise. That just was fascinating,” King said.
Hake also detected connective structures, called extracellular matrix, inside the spherical colony that were secreted by the choanos. Only then did it occur to Hake and King that these might not be the remains of bacteria the choanos ate, but bacteria living and grazing on stuff secreted by the colony.
Reference: “A large colonial choanoflagellate from Mono Lake harbors 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, 14 August 2024, mBio.
DOI: 10.1128/mbio.01623-24
