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INFLUENCE OF ROOT EXUDATES AND BACTERIAL METABOLIC ACTIVITY ON APPARENT CONJUGAL GENE TRANSFER FREQUENCIES IN THE RHIZOSPHERE OF WATER GRASS (ECHINOCLORA CRUSGALLI)
Citation:
Kroer, N., T Barkay, S. Sorenson, AND D. E. Weber. INFLUENCE OF ROOT EXUDATES AND BACTERIAL METABOLIC ACTIVITY ON APPARENT CONJUGAL GENE TRANSFER FREQUENCIES IN THE RHIZOSPHERE OF WATER GRASS (ECHINOCLORA CRUSGALLI). Presented at Presented at the 1995 Annual Meeting of the American Society for Microbiology, Washington, DC, May 21 - 25, 1995.
Impact/Purpose:
Presentation
Description:
The premise that genetic exchange is primarily localized in niches characterized by dense bacterial populations and high availability of growth substrates was tested by relating conjugal gene transfer of an RP4 derivative to availability of root exudates and bacterial metabolic activity. The rhizosphere of the marsh plant, Echinoclora crusgalli, was used as a model system. Pots containing muffled sand with and without a 2 wk old seedling were inoculated with 10 to the seventh power to 10 to the eighth power donors (Pseudomonas fluorescens) and recipients (Serratia sp.) per g of sand. To eliminate the indigenous bacterial flora, seeds were sterilized with AgNO3. Production of root exudates was demonstrated by measuring changes in DOC concentration in plant nutrient medium during plant growth. To demonstrate bacterial utilization of exudates, incorporation of 14C into donors and recipients from 14C-labelled exudates was determined. Metabolic activity of donors and recipients was measured by incorporation of tritiated leucine. The presence of plants greatly stimulated conjugal transfer. Apparent transfer frequencies (T/D*R) in the rhizosphere were 4-6 and 6-7 orders of magnitude higher than in sand of pots with or without a plant, respectively. Donors and recipients were able to utilize up to 14% of the root exudates. Average leucine uptake rates (fmol leu CFU-1 h-1) were 1.1 x 10-3 for rhizosphere, 4.5 x 10-4 for sand of pots with plants, and 3.1 x 10-4 for sand of pots without plant. These studies show that the rhizosphere of water grass is a niche where conjugal gene transfer is enhanced possibly due to stimulation of bacterial metabolism by root exudates.