In the depths of remote Antarctic lakes, tiny communities of microorganisms thrive where few other life forms can survive.
Scientists are studying these microbial structures to understand more about how life evolved on Earth.
One such place of interest is Lake Untersee, the largest freshwater lake in East Antarctica’s interior.
Lake Untersee is constantly covered by several meters of ice and gets very little sunlight for much of the year. Despite these harsh conditions, the lake hosts a rich ecosystem of microorganisms.
These microbes form peculiar structures on the lake bottom, ranging from narrow pinnacles to larger cone-shaped formations.
Understanding why these structures form in different shapes has long puzzled scientists, but a recent study published in Environmental Microbiology offers some answers.
Dr. Anne Jungblut, a microbial researcher and one of the study’s authors, explains, “Because Lake Untersee has these two different formations, it allows us to study how these microbial structures formed.
If the microbes in these structures are similar, it would suggest they are primarily shaped by environmental forces. But if they have different species, it could mean that the species themselves influence the shape.”
In the study, researchers took a closer look at the organisms making up these structures. Despite the ice cover, enough light reaches the lake’s depths to support photosynthetic life.
The top layer of these microbial structures is colorful due to photosynthetic organisms that capture the limited light. Below this layer, it looks like empty clay but is full of organisms that don’t rely on light for growth.
The researchers analyzed tiny samples from these structures, each weighing less than a gram. They extracted DNA to identify the different species present.
The samples contained a variety of single-celled organisms, including Archaea and more complex protists like microfungi, ciliates, and amoebas. The outer layers were mainly composed of cyanobacteria, a type of photosynthetic bacteria found in most freshwater ecosystems worldwide.
The two types of microbial structures were dominated by different kinds of cyanobacteria. The cone-shaped structures had more of the thicker cyanobacteria called Microcoleus, while the pinnacle-shaped structures had more of the thinner cyanobacteria called Elainellacea.
“We believe that cyanobacteria play a role in how these structures form,” says Anne.
“Their growth patterns seem to lead to different shapes, but we still need to explore why certain species grow in specific areas and how these microorganisms interact with each other.”
Studying these microbial structures helps scientists learn more about early life on Earth. Each year, the structures in Lake Untersee grow as microorganisms and sediment accumulate, forming large structures over hundreds or even thousands of years.
These formations are similar to ancient stromatolites, which appeared billions of years ago and are among the oldest known fossils.
Stromatolites, primarily made of photosynthesizing cyanobacteria, played a crucial role in creating the oxygen-rich atmosphere we depend on today.
By studying living microbial structures in extreme environments like Antarctica, scientists can gain insights into how life evolved and organized itself billions of years ago.
“Most habitats on Earth today have a lot of organisms that didn’t exist on early Earth,” says Anne. “Studying these structures in Antarctica helps us understand how life evolved in an environment that resembles early Earth conditions. Lake Untersee is unique because it has different shapes of microbial structures.
Learning about these structures can teach us how life evolved, formed, and organized itself, and how much it was influenced by environmental forces.”
