Bacteria living in deep underground environments

Danilo Anton

Submarine hydrothermal ecosystems consist of complex biological systems that only recently have been explored.

Many of these ecosystems are located deep underground, usually between 1,000 and 4,000 meters, settled along the ridges and other underwater volcanic areas.

They are fluid surging areas rich in hydrocarbons, sulfur compounds and other minerals.

Despite the apparent hostility of the conditions of temperature, pressure and chemical composition, these ecosystems have a rich biodiversity.

The species include mussels and clams larger than 30 centimeters long, huge tube worms with long stems (exceeding two meters long), stout crabs and other invertebrates. This ecosystem lies entirely in a rich bacterial flora.  

Energy sources in such environments are primarily based chemical type oxidation and hydration of hydrocarbons (in particular methane, generating methane hydrates) and hydrogen sulfide. In some cases fumes are hot, but there are places where there are cold springs of hydrocarbon fluids and sulfur compounds.

Many of these bacteria belong to the large group of archaea ( archaea ) including generically in the term 'hyperthermophilic bacteria'.

These bacteria can live in very high temperatures of 45 ^o. Celsius or more. Some even grow best at temperatures above 80^o .Celsius

T. Gold says their waxy membranes allow exchanges at high temperatures (with colder temperatures they harden and do not function properly).

The author notes that the boiling point of water on the surface is 100^o up to 300^o  just 876 meters deep in the sea. The critical point where the vapor and liquid phase of water-appears undifferentiated is 2,250 meters deep.

In many communities submarine hydrothermal water is a "supercritical" fluid and therefore there are no problems of water boiling that could affect the vital processes, as in the surface.

For that reason, says Gold, one can imagine that in the pores of rocks, deep, maybe even 6 or 10 km. there is a large population of hyperthermophilic bacteria using the available chemical energy which can be extracted from the oxidation of methane and other hydrocarbons.

Methane is a particularly desirable feeding fuel (for bacteria) because its density increases considerably. At a depth of 6 km methane is 400 times denser than on the surface. With this much higher density the chances of methane molecules passing through membranes 'archaea' they are far greater.

This deep biothermal system is what Gold called "deep hot biosphere" (the deep hot biosphere).

In many boreholes deep hyperthermophilic communities have been detected.  This author provides two examples: an oil well in Alaska where "active biology" was found at a depth of 4.200 meters and a temperature of 110^o C and a well of 5.200 meters in Sweden where the presence of anaerobic microorganisms was checked at temperatures of 60^o to 70^o.

In non-oceanic and sub-aerial environments hydrothermal vents depending on chemical energy also exist.

A known example are the hydrothermal springs of Yellowstone in North America. 

Thermophilic communities of these thermal lakes were studied in detail since the 1960s. One of these bacteria, Thermus aquaticus, was identified and described and allowed one the first replicas of DNA that enabled the development of molecular biological industry.

Bacteria that inhabit these mineral hot springs use oxidizing agents to develop their metabolism. These bacteria are the foundation of a particular ecosystem including several unicellular and multicellular organisms.

Although these submarine hydrothermal environments appear as anomalous and extreme environments, Gold thinks that they are a mere surface expression of an enormous deep biosphere.

This biiota would not be an oddity. On the contrary, it would be the most common form of life on Earth (and other planets as well).

This author argues, with strong arguments, that the vast majority of organisms base their metabolism on chemical energy, and that the true biological "rarity" is photosynthetic life.

Human beings are creatures of surface and have prejudice as surface beings. There is a prejudice in contemporary science that all life must be located on planetary surfaces. However, most of living process in our planet and in other planetary bodies as well take place underground.

The presence of surface life on Earth is a very rare phenomenon that occurs due to a very unusual combination of temperature, pressure and gas composition.

From: "Inexhaustible? Petroleum and Gas" Danilo Anton, Piriguazu Ediciones