THE LIVING SOIL: BACTERIA

Bacteria are tiny, one-celled organisms – generally 4/100,000 of an inch wide (1 µm) and somewhat longer in length. What bacteria lack in size, they make up in numbers. A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria. That is as much mass as two cows per acre.

Figure 1:  A ton of microscopic bacteria may be active in each acre of soil. Credit: Michael T. Holmes, Oregon State University, Corvallis.	Figure 2: Bacteria dot the surface of strands of fungal hyphae. Credit: R. Campbell. In R. Campbell. 1985. Plant Microbiology. Edward Arnold; London. P. 149. Reprinted with the permission of Cambridge University Press.

Bacteria fall into four functional groups. Most are decomposers that consume simple carbon compounds, such as root exudates (root exudates are the secretions plant roots put out into the soil) and fresh plant litter. By this process, bacteria convert energy in soils organic matter into forms that are useful to the rest of the organisms in the soil food web. A number of decomposers can break down pesticides and pollutants in soil. Decomposers are especially important in immobilizing, or retaining, nutrients in their cells, thus preventing the loss of nutrients, such as nitrogen, from the rooting zone.

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