What if the first bacteria weren’t the ones we thought?

However, it is very difficult to study these subsurface environments directly. But alkaline hydrothermal zones such as Prony Bay (New Caledonia) or Lost City (Mid-Atlantic Ridge) are considered to be ‘open windows’ into the deep biosphere. And the hydrothermal field in Prony Bay, located in a shallow lagoon, provides easier access to these environments.

In a recently published multidisciplinary study linking micro-imaging and microbial ecology, researchers from IPGP’s geomicrobiology team used a combination of different types of imaging to provide a detailed description of the mineralogy of the Prony Bay site and the microbial populations present in situ.

This study shows that the first bacteria to develop at the base of hydrothermal vents were heterotrophic bacteria that used the abiotic organic matter (carbonaceous) produced during serpentinisation. And not, as is generally accepted, autotrophic bacteria that metabolise CO2 rather than prior organic molecules.

As the bacteria identified (belonging to the Firmicutes family) are predominant at the base of the most recently formed vents, it is likely that they were carried down from the subsurface by the hydrothermal fluids rising towards the ocean floor. They would therefore constitute a sample of subsurface bacterial colonies.

Detailed imaging of the hydrothermal structure also shows that the bacterial networks created by the colony are involved in the early stages of chimney architecture.

These results are therefore leading us to rethink the structure and functioning of these particular ecosystems, and consequently those of the primitive environments in which life may have appeared.