Grantee Research Project Results
Assessing the Potential of Creating Biased Rhizospheres Based on Inositol RhizonpinesEPA Grant Number: U915029
Title: Assessing the Potential of Creating Biased Rhizospheres Based on Inositol Rhizonpines
Investigators: McSpadden-Gardener, Brian B.
Institution: Michigan State University
EPA Project Officer: Just, Theodore J.
Project Period: January 1, 1996 through January 1, 2001
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996)
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Botany/Plant Pathology
Particular microbial populations may be selectively enhanced by the introduction of specific organic nutrients into the rhizosphere environment. The objectives of this research project are to assess: (1) the impact of exogenous applications of the organic nutrient myo-inositol on rhizosphere bacterial populations; and (2) the potential for creating biased rhizosphere systems and evaluating their usefulness in specifically stimulating target populations of rhizosphere bacteria.Approach:
The rhizopine synthesis (mos) genes from Sinorhizobium meliloti L5-30 were used to generate rhizopine-producing transgenic plants. Rhizopines did not accumulate in transformed plant tissues, and molecular analyses indicated that not all of the cloned mos genes were properly expressed. An analysis of the cloned mos genes suggested that they were not sufficient for rhizopine accumulation in nodules. More information regarding the nature of rhizopine synthesis is required before a biased rhizosphere system based on rhizopine-synthesizing plants can be created. The abundance and source of rhizopine catabolic activity in the soil and rhizosphere environment also were investigated. The number of culturable bacteria capable of utilizing these compounds for growth was 1 to 10 percent of the number growing on complex media. A diverse set of novel rhizopine-catabolizing bacteria was isolated and characterized. Different bacteria that can catabolize the proposed nutritional mediators are present in the environment and may compete for these organic nutrients in situ. The impact of myo-inositol amendment on soil and rhizosphere bacterial populations was examined in growth chamber and field experiments. The application of the nutrient resulted in increases in the numbers of culturable bacteria. Amplified rDNA restriction analysis (ARDRA) and fluorescence-tagged ARDRA indicated that the abundance and composition of the bacterial communities changed in response to the amendment. Increases in the abundance and activity of S. meliloti were observed. These results indicate that nutrient amendments can be used to promote the growth and activities of targeted bacterial populations in the rhizosphere.Supplemental Keywords:
fellowship, rhizosphere, rhizopine, Sinorhizobium meliloti, organic nutrient, myo-inositol, microbial enhancement.