Monday, 10 July 2006 - 4:00 PM

Soil as a Public Health Threat or Savior.

Ian Pepper1, Deborah Newby2, Charles Gerba1, and Charles Rice3. (1) Univ of Arizona, 429 Shantz Building, #38, Tucson, AZ 85721, (2) Idaho National Engineering and Environmental Laboratory, 2525 Fremont Avenue, P.O. Box 1625, MS 2203, Idaho Falls, ID 83415, (3) Kansas State Univ, Dept of Agronomy, 2004A Throckmorton Hall, Manhattan, KS 66506

Traditionally soil has been viewed as a vehicle that provides food for the populations of the world. However, soils are multi-faceted and can influence human health and welfare in a variety of other ways than can be beneficial or potentially harmful. Soil serves as a very complex and rich environment for soil microorganisms. Here we evaluate four different aspects of soil that illustrate how soil can be viewed as a public health threat or savior. Infectious diseases are now the third leading cause of death in the United States. Changes in the demographics of sensitive populations and the rapid evolution of new and existing pathogens are a major challenge in controlling the environmental spread of infectious disease. Soil is the habitat of some significant pathogens (geo-indigenous), a means of pathogen transport (geo-transportable) and means of waste purification (geo-treatable). While there are only a few geo-indigenous pathogens, they are often very deadly (high mortality) or debilitating (e.g. Naegleria fowleri). Soil is important in the watershed and intercontinental transport of pathogens. Climate change will increase the geo-transport of pathogens in the future resulting in increased exposure of humans and animals. Concern over horizontal gene transfer has focused on the question Can antibiotic resistance genes be transferred from non-pathogenic bacteria to human pathogenic strains, particularly via conjugation? Such a transfer event would allow for the proliferation of antibiotic resistant bacteria capable of causing human infection that could not be controlled by the target antibiotic. In addition to the potential for transfer of antibiotic resistance, gene transfer in soils is also of interest because of its role in evolution and soil microbial community adaptation. We illustrate the role of selective pressure and selfish DNA in propagating horizontal gene transfer in soil, and a theoretical framework for microbial adaptation. Beneath the soil layer is an unsaturated zone referred to as the vadose zone, and below that the saturated zone, where groundwater resides. Soils are frequently the site for disposal of municipal and animal wastes through the process of land application and natural disasters such as hurricanes. These wastes are complex in nature, potentially containing microorganisms as well as organic and inorganic pollutants. The ultimate fate of these pollutants and their impact on the environment are directly dependent on the properties of the soil to which they are applied. It is commonly recognized that less than 1% of soil microorganisms are readily cultured and identified. Even with this under-representation, a wealth of products has been extracted from this microbial world. The first notable discovery related to human health was the discovery of antibiotics first achieved by Selman Waksman with the discovery of streptomycin for which he won the 1944 Nobel Prize. Soil organisms can provide an enormous range of applications to human health and welfare. For human health, an ever growing list of antibiotics has expanded into therapeutic and preventive agents for diseases, including cancer treatments. Soils are also a source for the production of catalysts, reagents and enzymes to improve industrial processes.

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