REU: A Molecular Approach to Understanding the Genetic Response of Soil Microbial Populations Under Selection

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Drs. William E. Holben and James M. Tiedje of Michigan State University propose taking a molecular approach to understanding gene ecology and exchange under an applied selection pressure -xenobiotic chemicals in the environment. Past research in microbial ecology has provided virtually no information on genetic changes of microbial populations in soil. This omission is particularly apparent, not that the issue of release of genetically engineered microorganisms has raised questions for which little data exists to underpin interpretations of risk. To study such change, an effective and ecologically sensible selection that can be followed at the DNA level is needed. The investigators have chosen the biodegradtion of a new energy resource -- herbicides -- as the system of study. They proposed to test the hypothesis that the native and soil microbial population is not genetically optimized for use of a new energy resource when first introduced, but that after repeated exposure, genetic changes will be selected that enhance the ability of populations to use these chemicals. By using gene-specific probes, DNA restriction analysis, hybridization and related molecular methods, they can distinguish among the five most likely genetic responses: (i) regulatory changes resulting in altered gene expression; (ii) a mutation which results in a new metabolic activity; (iii) rearrangement or amplification of genetic information; (iv) transfer of genetic information to similar organisms; (v) transfer of genetic information to dissimilatory organisms. While there is little doubt that these types of genetic changes that occur in the laboratory, there is little information on which are to prevalent changes that occur in nature, at what frequency and under what conditions. To provide this information, they propose to study these changes using chemostats, soil microcosms, field studies and a retrospective analysis of populations after 20 years of agrochemical treatment. This continuum of approaches should allow them to extrapolate information on mechanism and frequency between laboratory and field. Information on the latter is entirely lacking. This is extremely timely and much needed research by several groups in the scientific community (e.g., regulatory agencies) as well as by an industry struggling to make "safe" new organisms and their products by genetic manipulation. The investigators and their organization are world renowened for their expertise in this field.