Investigating microbialites to unlock the secrets of early life on Earth

Australian microbe research is helping improve our understanding of the potential for life in extreme environments, offering vital clues about early life on Earth.

Researchers hope the results will also inspire new solutions for carbon capture to mitigate climate change.

Led by Monash University, the University of Melbourne, and University College London and published in The ISME Journal, the study investigated microbialites, which are rock-like structures built by communities of microbes.

First author Dr. Francesco Ricci, a postdoctoral research fellow in the Monash Biomedicine Discovery Institute’s Greening Lab, said microbialites were among the earliest signs of life on Earth.

“What was new about the findings was that within these systems much biomass was produced using energy sources alternative to light,” Dr. Ricci said. “Our research reveals that these microbes aren’t just powered by sunlight, like most plants and algae.

“We think these ecosystems have been places where microbes came up with new ways to survive and make energy, helping shape the course of life on Earth.”

Co-corresponding author Dr. Bob Leung, also of the Greening Lab, said by studying the functions encrypted in the genomes of more than 300 microbial species and running lab experiments, many of these microbes were found to work together in highly efficient and complex ways.

“Their teamwork allows them to keep the system productive around the clock, even at night when photosynthesis stops,” Dr. Leung said. “Instead, they can tap into energy from chemicals in their surroundings, such as hydrogen, iron, ammonia and sulfur, allowing them to thrive even in complete darkness.”

Senior author Dr. Harry McClelland, from University College London, said, “We are looking for generalizable rules that govern organization and emergent function within these kinds of systems.

“One rule appears to be that the chemical potential energy that results from diffusive exchange between neighboring microenvironments can drive carbon fixation at significant rates, re-capturing CO₂ lost through respiration and maximizing community productivity.”

Dr. Ricci said the research could help inform new waste gas solutions.

“Many of the microbes we find inside microbialites are very efficient at consuming potent greenhouse gases like methane and carbon dioxide,” he said. “Tapping into these systems could provide new microbial solutions to, for instance, absorb industrial gaseous waste.”

Microbialites are structures built by a community of microbes. They usually rise above the sediment surface in the form of mounds or groups of mounds. Microbialites are categorized based on their internal structure—those with internal laminae or layering known as stromatolites, and structures with a clotted or “cauliflower” fabric called thrombolites.

Many of these microbes and the structures they build were very common during the Proterozoic Eon (2.5 billion to 538.8 million years ago). Living microbialites are mostly found in environments that other organisms cannot tolerate, such as salt lakes, sea bays with restricted water circulation, and hot springs. The Western Australian government says Australian examples of living microbialites include Hamelin Pool in Shark Bay, Lake Clifton near Mandurah, Lake Thetis near Cervantes and Lake Richmond, near Rockingham.