Canadian Rockhound: Microbial Communities Deep Below the Surface

Microbial Communities deep
below the Surface
By Dirk Schmid

For a long time, it was believed that the ground beneath our feet was generally void of any living organisms. Life is known to exist on the surface and in the uppermost soil layers. This region of life forms the biosphere. Within the last decade, however, geologists have found substantial populations of bacteria deep below the earth's surface. Evidence for the existence of life below the surface came during the late 1980's, when scientists began examining deep core samples. Both geologists and biologists are slowly improving their understanding about the role of bacteria and other life forms below the surface. This knowledge will be important in developing effective and practical solutions to cleaning up contaminated soils and groundwater. Scientists also believe that deep subsurface bacteria may be involved in the production or degradation of certain gases, such as carbon dioxide and methane, which are known greenhouse gases.

Earth's layers
Figure 1. The Earth consists of three basic layers: the crust, mantle and core. Life can only be found in the uppermost region of the crust. The intense heat and pressure below this region acts as a barrier to life. Life within the crust forms part of the living biosphere, which surrounds the earth.

Subsurface geomicrobiology
Figure 2. Generalized illustration of how surface bacteria
find their way into the earth's subsurface.

The Living Soil

The crust consists mainly of rock, but the uppermost part of the crust is composed of sediments and soils derived mainly from the weathering of rock. Soil used in agriculture typically consists of weathered minerals, humus and other organic matter, and pore spaces. The uppermost soil layers contain the greatest diversity of life forms. Bacteria, protozoa, worms, algae, fungi and parasites are typically found in these layers and are essential in maintaining a healthy soil ecosystem. Without bacteria, there would be no crops and dead organic material would accumulate by the tons.

Groundwater

Groundwater also contains bacteria. Currently, scientists at the University of Saskatchewan, Geological Sciences are studying the transport of bacteria in groundwater. The texture and structure of soil and sediments are important in that they determine the flow of water through the subsurface. Compact layers of clay contain tiny pore spaces, thus restricting the movement of bacteria and water. The large pore spaces in sand allows for increased groundwater flow.

Retrieving Samples

Bacteria have been found in mines at depths up to 2000 metres. Canadian scientists recently isolated bacteria from the groundwaters of two mines in the Canadian Shield. It is not known whether these bacteria are indigenous, or if they were introduced through mining activity. Geologists have also obtained bacteria from deep core samples. However, in many cases, the core samples became contaminated by surface bacteria as a result of exposure to drilling fluid. It is often very difficult to obtain contaminant free samples. Even more difficult, and sometimes frustrating is growing bacteria from the samples. Surface conditions come as a "shock" to subsurface bacteria, so care must be taken. Few scientists have successfully tried to identify species or measure the diversity of microorganisms from the subsurface.

Petroleum Eating Bacteria?

There is evidence that bacteria are responsible for the breakdown of petroleum beneath the surface. The Alberta oil sands are also believed to be the result of microbial activity. A better understanding of how these bacteria degrade petroleum will help environmental scientists to plan more effective and practical strategies for removing petroleum pollutants from soils and water.

Subsurface bacteria
Figure 3. Bacteria isolated from soil sediments, at depth 1.5 metres. Many spores can be seen in addition to the living bacteria. Spores are a mechanism of survival bacteria use under adverse environmental conditions. Photograph taken by Dirk Schmid, ©1996.

Microbial Communities

Bacteria below the surface do not have an easy life. Life is very hard. Food is usually scarce, and water is essential for any life form to exist. Under extreme environmental conditions, different species of bacteria will freely associate with one another (self-organize) to form communities. Communities are more than just a mixture of different species. Like cells, they appear to behave as evolving proliferating units. Complex relationships are formed between species as well. Exchange of DNA (the genetic code found in living organisms) can occur between species, thus increasing genetic diversity. The members within communities use different strategies for making and utilizing food. In certain cases, growth slows down dramatically to conserve energy and resources. When conditions become favourable again, the community may decline, as members freely disassociate from it and go their separate ways.

Trends

As a consequence of the recent findings discussed above, new disciplines have emerged. Geomicrobiology looks at microbial life within the earth, and the interactions between bacteria and rocks and minerals. Microbial Ecology deals with the study of microbial communities and the interactions between microorganisms and their environment. Within the next couple of decades, research will be more interdisciplinary and will focus on the cleanup of contaminated soils and groundwaters, as well as the importance of microbial communities in wastewater and subsurface ecosystems.

This article may not be copied, distributed or reprinted in any form without the author's permission. To contact the author, please use the e-mail address provided. If you are unable to contact the author, please contact the Canadian Rockhound. Authorized reprints must acknowledge the author, the original source and the Canadian Rockhound, and include the website URL address of the Canadian Rockhound.

This article was originally published in the Summer 1997 newsletter of the Saskatoon Lapidary & Mineral Club. Reprinted with permission from the author and editor. Drawings and photograph were provided courtesy of Dirk Schmid.