2024-01-05 13:08:20
Image of Navifusa majensis, microfossil from the McDermott Formation in Australia. This 1.75 billion year old microfossil contains thylakoids, which allow it to be identified as a cyanobacteria. Credit: Emmanuelle Javaux
Researchers from the Early Life Traces & Evolution laboratory at the University of Liège have identified photosynthetic structures within fossil cells 1 and 1.75 billion years old. These structures, called thylakoid membranes, are the oldest ever discovered. They push back the fossil record of thylakoids by 1.2 billion years and provide new information on the evolution of cyanobacteria responsible for the accumulation of dioxygen (O2) on Earth. This major discovery is presented in the journal Nature.
C
atherine Demoulin, Yannick Lara, Alexandre Lambion and Emmanuelle Javaux from the laboratory Early Life Traces & Evolution of the Research Unit Astrobiology at ULiège examined microfossils called Navifusa majensis (N. majensis) in shale from three formations in DR Congo and Canada dating back 1 billion years and in Australia dating back 1.75 billion years. In microfossils from the Canadian and Australian formations, ultrastructural analyzes revealed the presence of internal membranes whose arrangement, fine structure and dimensions allow them to be interpreted without doubt as thylakoids, where oxygenic photosynthesis occurs. This made it possible to elucidate the identity of N. majensis as thylakoid cyanobacteria.
This discovery thus puts into perspective the role of cyanobacteria equipped with thylakoid membranes in the oxygenation of the Earth. The presence of dioxygen played an important role in the evolution of early life but the timeline of the origin of oxygenic photosynthesis and the type of cyanobacteria involved during the Great Oxygenation Event (GOE), regarding 2.4 billion years ago, are debated (proto-cyanobacteria? cyanobacteria with or without thylakoids?). The discovery by ULiège researchers offers a new approach to solving these questions.
« The oldest known thylakoid fossils were around 550 million years old. Those that we have identified therefore make it possible to push back the fossil records by 1.2 billion years », explains Professor Emmanuelle Javaux, paleobiologist and astrobiologist, director of the laboratory Early Life Traces & Evolution at ULiège.
« The discovery of preserved thylakoids within N. majensis provides direct evidence for a minimum age of approximately 1.75 billion years for the divergence between thylakoid-bearing and thylakoid-less cyanobacteria. »
But the discovery of the ULiège team suggests the possibility of discovering thylakoids in even older fossil cyanobacteria, and of testing the hypothesis according to which the development of thylakoids might have played a major role at the time of massive accumulation of oxygen on Earth, around 2.4 billion years ago. This approach also makes it possible to examine the role of oxygenation in the evolution of complex life (eukaryote) on our planet and the origin and diversification of the first algae containing chloroplasts derived from cyanobacteria.
« Microscopic life is beautiful and is the most diverse and abundant form of life on Earth since the origin of life. Studying its fossil records with new approaches allows us to understand how life has evolved for at least 3.5 billion years. Some of this research even tells us how to search for traces of life beyond Earth !”, concludes Emmanuelle Javaux.
Scientific reference
Demoulin , CF , Lara , YJ , Lambion , A . et al. Oldest thylakoids in fossil cells directly evidence oxygenic photosynthesis. Nature (2024).
Contacts
Catherine Demoulin
Yannick Lara
Alexandre Lambion
Emmanuelle Javaux
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