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

A growing number of studies tend to show that colonies of bacteria live in the first few hundred meters or even kilometers beneath the surface of the Earth's crust. In these environments beyond the reach of the sun, they draw their energy from chemical reactions between rocks and the fluids circulating within them.

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

Photograph of an ancient hydrothermal vent in Baie de Prony (New Caledonia).

Publication date: 24/03/2017

Press, Research

Related themes : Origins

Environments in serpentinisation zones (chemical processes in which mantle rocks, as they rise to the surface, are transformed by interactions with hydrothermal fluids, releasing carbonaceous molecules) are particularly conducive to this underground life and are often considered to be good analogues of the environments in which life first appeared on Earth.

a) Photograph of an ancient hydrothermal vent in Baie de Prony (New Caledonia) sampled by IRD divers, and (b) of an emerging vent characterized during this study, and whose thin-slice observation by optical microscopy (c) reveals an interlacing of mineralized bacterial filaments.

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.

Microbial filaments belonging to the Firmicutes phylum and mineralized with brucite, in the inner conduit of a juvenile chimney in the Baie de Prony hydrothermal system. These were highlighted by (a) scanning electron microscopy and (b) Confocal Laser Scanning Microscopy. Green fluorescent labelling revealed the presence of DNA and therefore of microbial cells within the mineralized sheaths.

 

Ref: Céline Pisapia, Emmanuelle Gérard, Martine Gérard, Léna Lecourt, Susan Q. Lang, Bernard Pelletier, Claude E. Payri, Christophe Monnin, Linda Guentas, Anne Postec, Marianne Quéméneur, Gaël Erauso, Bénédicte Ménez – Mineralizing Filamentous Bacteria from the Prony Bay Hydrothermal Field Give New Insights into the Functioning of Serpentinization-Based Subseafloor Ecosystems: http: //journal.frontiersin.org/article/10.3389/fmicb.2017.00057/full

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