407-million-year-old bacteria species were first to colonize land

The team used light microscopy and super-resolution confocal laser scanning microscopy to study a new population of Rhynie cyanobacteria. Langiella scourfieldii, belonging to the Hapalosiphonaceae family, is a species of cyanobacteria that thrived among early land plants over 400 million years ago during the Early Devonian period.

Earliest evidence of land colonization

One of the main characteristics of Langiella scourfieldii is the presence of ‘true branching.’ This occurs when individual bacteria grow alongside each other in a line, with some lines breaking off in different directions to create a branching structure, explained the researchers in the press release.

Although Cyanobacteria is a fairly common component of the Rhynie Chert, many do not display this ‘true branching.’ By finding it in L. scourfieldii, researchers could confirm the bacteria's presence in this ecosystem.

“With the 3D reconstructions, we were able to see evidence of branching, which is a characteristic of Hapalosiphonacean cyanobacteria,” said Dr. Christine Strullu-Derrien, a scientific associate at the Natural History Museum and lead author of the study. 

“This is exciting because it means that these are the earliest cyanobacteria of this type found on land,” she added.

When the Earth was formed about 4.5 billion years ago, it had immensely different conditions than today. Its atmosphere was made up of carbon dioxide, methane, and water vapor. Cyanobacteria slowly released oxygen and changed the composition of the atmosphere to what it is today. This event is known as the Great Oxidation/Oxygenation Event, which occurred sometime between 2.4 – 2.1 billion years ago.

“Cyanobacteria in the Early Devonian played the same role that they do today,” added Christine. “Some organisms use them for food, but they are also important for photosynthesis. We have learnt that they were already present when plants first began colonizing land and may have even competed with them for space.”

The study was published in the journal iScience.

Study abstract:

Cyanobacteria have a long evolutionary history, well documented in marine rocks. They are also abundant and diverse in terrestrial environments; however, although phylogenies suggest that the group colonized land early in its history, paleontological documentation of this remains limited. The Rhynie chert (407 Ma), our best preserved record of early terrestrial ecosystems, provides an opportunity to illuminate aspects of cyanobacterial diversity and ecology as plants began to radiate across the land surface. We used light microscopy and super-resolution confocal laser scanning microscopy to study a new population of Rhynie cyanobacteria; we also reinvestigated previously described specimens that resemble the new fossils. Our study demonstrates that all are part of a single fossil species belonging to the Hapalosiphonaceae (Nostocales). Along with other Rhynie microfossils, these remains show that the accommodation of morphologically complex cyanobacteria to terrestrial ecosystems transformed by embryophytes was well underway more than 400 million years ago.