Deep drills into millions of years-old volcanic rock of the Deccan Traps in peninsular India have unearthed a teeming microbial community 1,500 metres below the earth’s surface.
The array of microbes, surviving in an environment starved of nutrients, where temperatures are torrid and the pressure intense, has chosen a lifestyle that may offer clues to mitigating climate warming and energy-related challenges.
The Deccan Traps, in the Krishna-Godavari river basin, is in one of the largest volcanic provinces in the world – an area covered with layers and layers of lava from massive volcanic eruptions nearly 65 million years ago. The Traps span an area of around 500,000 square kilometres.
In the Koyna-Warna region of the Deccan Traps, scientists at the Indian Institute of Technology, Kharagpur have extracted long cylinders of rock by core-drilling and sequenced the DNA of the microbes dwelling in the ancient rockpiles.
The microbes cannot afford to be fussy in those extreme habitats. The ultra-slow growers exhibited remarkable flexibility in using the limited number of chemical building blocks (such as oxygen and carbon) available for their survival, explained Pinaki Sar of the Indian Insititute of Technology, Kharagpur. The findings are documented in a study published in the journal Scientific Reports.
“From the present data in hand, it can be said that the microbes in the deep Deccan subsurface are capable of using carbon dioxide and/or bicarbonate which is one of the key players in global warming,” Sar told Mongabay-India. “The ability to form minerals (biomineralisation) is also observed in many microbial populations. These processes are complex like any other biological processes and need further investigation and validation.”
Sar is part of the global research program, Deep Carbon Observatory that seeks to understand the quantities, movements, forms, and origins of carbon in Earth.
A window into the past from the deep
Expanding on the importance of work, Sar said microorganisms in such extreme habitats (high temperature and pressure, lack of water, amount of organic carbon, levels of other nutrients) hold secrets of the past including clues for the origin of life.
“They also provide insights into the mechanisms of survival, their biogeochemical role in element cycling and other planetary processes,” he said.
The Deccan Traps provide a unique geologic setting: ranging from 65 million-year-old basalt layers to around 2.5-billion-year-old underlying basement (granitic) rock.
“The geologic settings of different subsurface formations not only influenced the microbial lifestyle but also structured the microbial community in a unique fashion,” said Sar.
DNA sequencing studies (shotgun metagenomics) revealed that bacterial members belonging to the taxonomic groups Proteobacteria, Actinobacteria and Firmicutes make up the three major populations of the deep biosphere in the Deccan Traps.
In fact, members of these taxa are the most frequently observed bacterial members of the deep life communities of other deep subsurface environments such as the Fennoscandian Shield in southeastern Sweden.
Sar and colleagues believe that tectonic disturbances at some point in the 65 million year history of the Deccan Traps rocks may have enabled fluids to squeeze through the dense basalt layers introducing microbes.
While probing the communities of microbes living in the basalt from the Deccan Traps, the underlying basement rock, and the thin transition zone between them, Sar and colleagues stumbled upon something interesting.
“There is not much of a difference in the nature of microorganisms between the basalt and the granite. But what is varying is the microbial networks – how different species interact with each other,” remarked Sar, referring to the high-throughput 16S Ribosomal RNA sequencing method that was applied to mine data on microbial diversity and interactions.
This interaction is reflected in the way the bacterial species process resources available on hand: the microbes are mostly tapping into the limited amount of nitrogen, sulfur, and hydrogen that are available in the oxygen-deficient surrounding to survive.
The researchers believe the microbes are also “picking up and recycling each other’s metabolites to survive in these isolated environments, with slightly different communities having evolved in basalt and basement rock.”
Further, their analyses showed a higher abundance of genes related to metabolic pathways for using bicarbonate, which could mean bicarbonate likely is the major carbon source for the Deccan Traps microbes.
New frontiers in carbon capture and storage
“In the backdrop of climate change, deep subsurface microbiome of these horizons are found to be highly relevant due to their potential for carbon dioxide sequestration, methane oxidation, metabolism of one-carbon compounds (such as methane) and thus could provide useful resources for mitigation energy-related challenges as well,” said Sar.
Owing to the enormous potential of these subsurface organisms in carbon metabolism, bioprospecting for organisms or enzymes involved in the formation of liquid biofuel (hydroxymethyl from methyl) could be immensely important, he said.
There is context to Sar’s contention. The idea of injecting carbon dioxide into volcanic rock basalt has been gaining momentum worldwide for fighting carbon emissions.
Several pilot projects conducted in different parts of the globe (such as in the Columbia River Basalt formation in the US and Northeast German Basin, Ketzin, Germany have sought to test the viability of the carbon capture and storage procedure and role of subsurface microbes in such processes.
“Because of its nature, basalt is considered a sink for carbon dioxide. But microbes that can lock in carbon dioxide as those found in the Deccan Traps can help safely store carbon dioxide on a long-term basis. So, the basalt formation with its microbial community may enhance the sustainability of a CCS [carbon capture and storage] procedure,” added Sar.
This article first appeared on Mongabay.
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