CleanBeta

Extreme Environments — Life without Light

Scientists are studying obscure, self-sustaining, bacterial communities that live extreme environments. These bacteria have evolved to flourish in conditions previously thought incompatible with life. For instance, “chemoautogrophs” are bacteria that do not depend on light for life.

Humans and most other land-dwelling organisms ultimately get their energy from the Sun, with photosynthetic plants forming the base of the food web.

In places that lack sunlight, life needs to find other energy sources. Other communities of “chemoautotrophs”-a word chained together from Greek roots meaning “chemical self-nourishment”-have been found in exotic places such as aquifers, petroleum reservoirs, and vents linked to deep-sea volcanoes. Yet these communities all depend at least in part on nutrients that can be traced back to photosynthetic plants or bacteria.

One breed of bacteria was recently discovered “almost two miles deep beneath the surface in a South African gold mine. It is the first microbial community demonstrated to be exclusively dependent on geologically produced sulfur and hydrogen and one of the few ecosystems found on Earth that does not depend on energy from the Sun in any way. The discovery, appearing in the October 20 issue of Science, raises the possibility that similar bacteria could live beneath the surface of other worlds, such as Mars or Jupiter’s moon Europa.”

Using genetic tools, the team discovered that there is very little species diversity in the rock fracture community. Compared with bacteria in the water used for mining, the fracture water is dominated by one type of bacteria related to Desulfotomaculum, which is known to get energy from the reduction of sulfur compounds.

“We also believe that the sulfate used by these creatures is left-over from ancient groundwater mixed with ancient hydrothermal fluid. We can detect that because the chemical signature arises from interacting with the fracture’s wall rock,” commented Rumble. “It is possible that communities like this can sustain themselves indefinitely, given enough input from geological processes. Time will tell how many more we might find in Earth’s crust, but it is especially exciting to ponder whether they exist elsewhere in the solar system.”