<OL> <LI> Investigate the population dynamics of Escherichia coli O157:H7 on plant roots grown under various irrigation water salinity regimes in the field and growth chamber.<LI>Investigate persistence of E. coli O157:H7 in soil, irrigation water, and rhizophere under different environmental conditions. <LI>Utilize fluorescence-activated cell sorter (FACS) technologies to determine genes that are specifically expressed by E. coli O157:H7 cells on plant surfaces. <LI> Construct knock-out mutations in E. coli O157:H7 genes that are specifically expressed in the root and test their involvement in survival and interactions with indigenous microflora. <LI>Develop predictive models for E. coli O157:H7 persistence/survival in soil and on plants grown under field conditions.
Approach: We will use fluorescence microscopy methods to quantitatively study the population dynamics of enteric bacteria on plant surfaces that will show the interactions of O157:H7 strains with indigenous microorganisms and the location of this pathogen in particular microsites and high-throughput fluorescence-activated cell sorter (FACS) to identify genes up-regulated by E. coli O157:H7 cells on plant. We will also use specific real time PCR probes to quantitatively monitor survival/persistence of E. coli in soil, rhizosphere, and on leaf surfaces. Specific evaluations of persistence of E. coli O157:H7 in the lab, growth chamber, and lysimeters at different irrigation water qualities, salinity and other environmental conditions will be determined. Finally, we will model the interaction between environmental factors, population changes, and genes that are expressed during growth of bacterial pathogens in the rhizosphere and on leaf surfaces.