Microbial structures in an Antarctic lake could reveal more about how life evolved

A community of microorganisms thrives in the depths of remote Antarctic lakes, where few life forms survive. Scientists are studying the structures created by these communities to understand more about microscopic life in these extreme environments, which may provide clues about how life evolved.

Lake Untersee is the largest freshwater lake in the interior of East Antarctica.

With its surface permanently buried under several meters of ice and limited exposure to sunlight for most of the year, the lake is devoid of larger organisms such as plants and animals. However, the rich ecosystem in its depths helps scientists better understand how life evolved on our early planet.

Vast communities of microscopic organisms form special structures on the bottom of the lake, from those in the shape of small narrow peaks to larger cone-shaped structures. Why they form in two different shapes has been a mystery to scientists, but a recent study published in Environmental microbiology tries to answer this question.

Dr. Anne Jungblut, microbial researcher at the museum and author of the study, says: “Because the Untersee lake 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 indicate that they are primarily shaped by environmental forces. But if they have a different species composition, it could mean that how these species grow has a greater influence on the shape of these structures.”

“Because these two structures grow side by side in the same environment, we think that the microbial species play a greater role in influencing the shape of the structure. So in this study, we wanted to take a closer look at the organisms that form these structures.”

What do these structures consist of?

Although Lake Untersee is permanently covered with ice, just enough light penetrates the depths of the lake to allow photosynthetic life to survive.

The top layer of these microbial structures is very colorful because it is full of photosynthetic organisms that create pigments that help capture the little light that reaches the bottom of the lake. Beneath this layer, it looks like empty soil, but it is also full of various organisms that do not use light to grow.

The researchers analyzed several small samples, each weighing less than one gram, to learn more about the species that make up these different structures. They then extracted the DNA and used it to assemble the genomes of different species to see what was present.

The samples contained a variety of single-celled organisms such as Archaea and more complex protists such as microfungi, ciliates and amoebae. The outer layers were largely made up of cyanobacteria, a type of photosynthetic bacteria found naturally in most freshwater ecosystems around the world.

The two types of microbial structures were dominated by two different types of cyanobacteria. The cone-shaped structures contained a higher number of the thicker Microcoleus cyanobacteria and the peak-shaped structures contained a higher number of the thinner Elainellacea.

“Based on our research, we believe that cyanobacteria play a role in how these structures form,” says Anne. “So there must be some way they grow that leads to these different shapes.”

“But we don’t yet know why there are certain areas of the lake where different species grow and how these different microorganisms interact with each other. This is something we want to explore in our future research.”

How can these microbial structures tell us more about early life on Earth?

Every year, the microbial structures in Lake Untersee continue to grow as the combination of microorganisms and fallen sediments form layers that can form large structures over hundreds and possibly thousands of years.

These soft microbial structures form similarly to stromatolites, which first appeared on our planet billions of years ago and are among the oldest known fossils.

Although stromatolites still exist today, they are best known as a primary feature of the Archean, which spanned 4 to 2.5 billion years ago. During this time, there were no plants, animals, or other complex organisms that we see today.

The only life that existed was unicellular. Many Archean stromatolites were also formed by photosynthesizing cyanobacteria and are thought to be largely responsible for the oxygen-rich atmosphere we depend on today.

Scientists are taking the opportunity to study living microbial laminated structures to try to learn more about how life evolved during this early period of Earth’s history.

“Most habitats on Earth today have many organisms that did not exist on early Earth,” says Anne. “So we’re studying these structures in Antarctica because it’s an extreme environment where not much can live, so it better reflects what it would have been like during the Archean.”

“Lake Untersee is unique because it has these different shapes of microbial structures. Studying these structures can help us learn more about how life evolved, shaped and organized itself, and how much it was influenced by environmental forces.”

This story is republished with the kind permission of the Natural History Museum. Read the original story here.