A research team investigated some of the earliest fossils from thin samples from the famous Rhynie chert fossil site in Aberdeenshire, Scotland. Their study led them to discover the oldest species of cyanobacteria known to have dominated the land.
Cyanobacteria have a long history of evolution recorded in marine rocks, and they are also abundant and diverse in terrestrial environments. While phylogenies suggest that this group of bacteria dominated the land early in its history, there is limited paleontological documentation.
Ancient Bacteria Fossils
The Rhynie chert has the best-preserved record of early terrestrial ecosystems. It provides opportunities to understand cyanobacterial diversity and ecology better as plants begin to thrive on the land surface. The researchers are fortunate enough to find new samples from Rhynie chert containing cyanobacteria that they can study in more detail using a confocal microscope.
In the study, the researchers use light microscopy and super-resolution confocal laser scanning microscopy to investigate a new population of Rhynie cyanobacteria. They identified the bacteria species as Langiella scourfieldii, a microorganism that belongs to the Hapalosiphonaceae family. This type of cyanobacteria thrived among early terrestrial plants more than 400 million years ago during the Early Devonian period.
One of the main features of Langiella scourfieldii is the presence of "true branching." This characteristic occurs when individual bacteria grow alongside each other in a line. Some lines break off in various directions and create a branching structure.
While cyanobacteria are a common component of the Rhynie chert, many do not display the true branching feature. By finding this characteristic in Langiella scourfieldii, scientists can confirm its presence in this ecosystem.
Led by Dr. Christine Strullu-Derrien, a scientific associate at the Natural History Museum, the researchers used 3D reconstructions in visualizing the evidence of branching. Their findings confirm that these species are the earliest cyanobacteria on land.
Understanding Early Land Ecosystems
Cyanobacteria are considered the earliest forms of life on Earth. Commonly known as blue-green algae, they are responsible for the transition of our planet's atmosphere from carbon dioxide to oxygen-rich. These bacterial species can be found in water streams, wetlands, ponds, rivers, and lakes, significantly shaping life.
When the Earth was formed 4.5 billion years ago, it had very different environmental conditions than today. Its atmosphere was composed of water, methane, and carbon dioxide. Oxygen was slowly released by cyanobacteria, changing the composition of the atmosphere to what it is today. This is known as the Great Oxidation/ Oxygenation Event, which was believed to have occurred about 2.4 to 2.1 billion years ago.
Strullu-Derrien added that the cyanobacteria in the Early Devonian period played the same role that they do today. Some organisms use them as a food source, but they are also significant in photosynthesis. Scientists believe cyanobacteria existed when plants began to thrive on land and may have even competed with them for food.
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