微生物学：微生物が海底下で生き続けるための仕組み

The discovery of microbial communities up to 750 metres below the seafloor provides insights into how these microorganisms are able to survive in this extreme environment. These findings are published in Nature this week.

Microorganisms are known to be present in the Earth’s upper crust, but limited information exists about the lower oceanic crust. It is challenging for microbiota living in rock under the seafloor to survive because of the difficulties in obtaining sufficient amounts of carbon and energy for growth and other processes.

Virginia Edgcomb and colleagues obtained rock samples from below the seafloor at the Atlantis Bank in the Indian Ocean, where the Earth’s lower crust is exposed. Here, the authors discovered active microbial communities in the exhumed lower oceanic crust. On the basis of enzyme activity measurements and mRNA recovery from these microorganisms, they determined that levels of cellular activity were very low. They identified unexpected heterotrophic processes (using organic material as a source of food), such as the recycling of amino acids to produce compounds that can be used in energy production and storage. They suggest that these adaptations reflect the competition for limited and sporadically available resources in the deep biosphere.

The authors note that further exploration of the lower oceanic crust is required to determine whether the diversity and activities of microbiota are similar to those found below the Atlantis Bank.