‘First contact’ that may have led to complex life on Earth finally witnessed by scientists
- Written by The Conversation
On the shores of the west coast of Australia lies a window to our past: the stromatolites and microbial mats of Gathaagudu (Shark Bay).
To the untrained eye they look like a collection of rocks and slime – but they are in fact teeming with microbial life. And these stromatolites are living “relics” of ancient ecosystems that thrived on Earth billions of years ago.
If you wade past, it feels like you’re walking back through time. In fact, the first bubbles of oxygen that filled the atmosphere on early Earth likely came from ancient stromatolites. You could say we owe our very existence to these piles of rocks.
So, what other secrets of our past could these ecosystems tell us? Through decades of research, we know how early life has woven its path through these “living rocks”. But most recently our team embarked on the greatest genealogy search of them all: searching for our great microbial ancestors, the Asgard archaea.
And in a new paper, published today in the journal Current Biology, we report how this search led to the discovery of a key clue that could help explain how complex life evolved on Earth.
The cells that comprise complex life
Asgard archaea were originally named after Norse gods. This fascinating group of microbes sits on the cusp of one of the most significant events in the evolution of life: the origin of the complex cells that make up plants and animals, known as eukaryotes.
Evidence suggests Asgard archaea are the closest relatives of eukaryotes. And that on an early Earth it was the “marriage” of an ancient Asgard archaeon and a bacterium that led to the first eukaryotes.
They formed an ancient partnership. They shared resources and physically interacted, leading to the first complex cells. Like a Romeo and Juliet tale of two distant families coming together, Asgard archaea and bacteria decided it was time to break from traditional family values.
But we have never seen a model of how this may have occurred. Until now.
Holding up a mirror to the ancient past
Our team used the mats of Shark Bay as a “seed” to establish cultures of these ancient microbes. We are one of only four groups worldwide to achieve this, through years of research with a dedicated team of graduate students nurturing the Asgards like offspring.
But the Asgards were not alone. We found them together with a sulphate-loving bacterium. Could this be a model of how complex life may have started on a primitive Earth?
We began by sequencing the Asgards’ DNA to decipher exactly how these microbes tick at the genetic level. We also used artificial intelligence to model how proteins could have behaved in a world before eukaryotes. Evidence suggested these two microbes were sharing nutrients. In other words, they were cooperating.
But we wanted to delve deeper. What do our great microbial ancestors look like? Here we turned to electron cryotomography, a high-resolution imaging approach that allowed us to observe cells and structures at a nanometre scale.
And here we showed – for the first time – an Asgard archaeon and a bacterium directly interacting. Tiny nanotubes were connecting the two organisms – perhaps reflecting what their great-ancestors did on an early Earth that ultimately led to the explosion of complex life as we know it.
Weaving western science with Indigenous knowledge
This was a major discovery – one that originated in Gathaagudu, a World Heritage Site with significant environmental and cultural values.
Aboriginal people first inhabited Gathaagudu over 30,000 years ago. We wanted to recognise and celebrate the language of the Malgana people, one of the traditional language groups of Gathaagudu. We also wanted to connect western science with Indigenous Knowledge in a meaningful way.
To this end and working closely with the world’s foremost Malgana language expert, Kymberley Oakley, and Aboriginal elders, a name was granted for our novel Asgard archaeon from the language of the Malgana people: Nerearchaeum marumarumayae. The species name – marumarumayae – is derived from the Aboriginal language of the Malgana people, meaning “ancient home”, a reference to stromatolites being of ancient origin in Earth’s history.
Weaving Aboriginal language into the naming of our new microbe represents a fitting connection between unique Aboriginal culture in Australia and the ancient microbe discovered that calls the mats of Gathaagudu “home”.
Gathaagudu is under threat from global change, from increased heatwaves, cyclonic events and human activity. And among the values to preserve and conserve are the significant Aboriginal connections as well as the trails of life going back through evolutionary time.
With our study we have peered into our past. And maybe like the Montagues and Capulets of Shakespeare, we see distant families of microbes coming together to bridge the divide and ultimately form the early eukaryotes that eventually led to us: a fragile branch on the evolutionary tree of life.
