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United States Department of Agriculture

Agricultural Research Service

2010 Annual Report

1a.Objectives (from AD-416)
Detection, quantification, and characterization of pathogen behavior in different environmental matrices; determine inactivation/survival rates and transport characteristics of fecal coliform and pathogens from manure sources to surface or ground water; determine sources of nonpoint fecal pollution at the Santa Ana River Watershed by bacterial source tracking technology; quantify important mechanisms influencing the transport and retention of pathogenic microorganisms in subsurface environments; adapt and improve numerical models for simulating the environmental transport and fate of pathogenic microorganisms; and develop and optimize manure and lagoon water treatment strategies to minimize the transmission of pathogenic microorganisms to food and water resources.

1b.Approach (from AD-416)
Conduct laboratory, lysimeter and field experiments to examine the important physical, chemical, and biological processes affecting the fate and transport of pathogenic microorganisms in manure-soil-water systems. Laboratory studies will determine the important processes and mechanisms affecting pathogen survival. Studies will be conducted at various scales using culture and molecular approaches to investigate pathogen movement in surface water and soil. Measurements of pathogen concentration, soil and environmental conditions will be collected to allow the simulation of pathogen transport. As new information becomes available, existing models will be improved to enhance the prediction of pathogen transport to surface water, ground water, and the environment. Coupling laboratory and field scale experiments with simulation studies, new strategies will be developed to control the movement of pathogenic microorganisms from animal feeding operations to human food and the environment. Research will be conducted in collaboration with the Food Safety Research, WRRC, Albany, CA. 5310-42000-002-00D (5/01).

3.Progress Report
1. Research pertaining to pathogen transport in unsaturated porous media and experiments to predict pathogen fate in heterogeneous systems was conducted in previous FYs, leading to a total of 10 related publications. During this reporting period significant research was conducted to address pathogen transport at various scales; and to refine, and adapt computer models. Research focused on: (1) pore scale simulations to determine the applied hydrodynamic torque that controls pathogen immobilization and rolling; (2) determining the influence of cation exchange on the release of clay and bacteria, and colloid-facilitated transport; (3) factors that influence pathogen retention hysteresis (Debye length, chemical heterogeneity, and colloid concentration); and (4) development of pore (particle trajectory analysis in a constricted tube), network, and continuum scale models that accurately account for pore-scale physics.

2. Research was conducted to evaluate a rapid method for quantifying assimilable organic carbon (AOC) in soil. This is a follow up study that was conducted last year on AOC in surface water and was a collaborative effort by researchers from University of California Riverside and the United States Salinity lab. Assimilable organic carbon (AOC) might be an important factor controlling the regrowth potential of both beneficial and pathogenic microorganisms in soil, just as it is in water. In this study, a simple and fast method to determine AOC in soil was developed using a luminous microorganism Vibrio harveyi BB721, whose luminescence is independent of cell concentration. It was found that the luminescence intensity of starved bacteria at late growing phase was proportional to the concentrations of glucose added. Light intensity of the cells was highly pH dependent and the optimal pH was around 7.0. Heavy metals, lead, cadmium, arsenate, chromium, nickel, copper, zinc, cobalt, and manganese (up to 20 mg kg-1 soil equivalent) had little effect on light emission, while mercury concentrations as low as 2.0 mg kg-1 soil significantly inhibit the light emission. Our data showed that AOC in soil is the dominant factor controlling soil microbial biomass and regrowth.

1. Pore-Scale Simulations: Recent research indicates that microorganism retention in soil is a complex process that depends on forces associated with water flow and chemical properties. ARS researchers at Riverside, CA, conducted studies to quantify and predict the forces due to water flow that act on microorganisms adjacent to soil surfaces. This was accomplished through detailed pore-scale simulations of water flow in sphere packs, in conjunction with newly developed theory. This information was subsequently used to determine the fraction of the solid surface area that can contribute to retention and the corresponding maximum solid phase concentration of attached microorganisms for given water flow and chemical conditions. This information will be of interest to scientists and engineers concerned with predicting the fate of microorganisms in the environment.

2. Association of Enterococcus species and antibiotic resistance with specific pollutant sources. Enterococci are widely used as indicator of fecal contamination of waterways in most urban areas throughout the United States, and exposure of these bacteria to excessive antibiotics may become a serious public treat. This research was conducted at the USDA-ARS-U.S Salinity laboratory in Riverside to investigate the influence of pollutant sources on Enterococus population and resistance to a number of antibiotics. Enterococcus species showed multiple resistances to ciprofloxacin, Erythromycin, and tetracycline, and resistance to tetracycline was prevalence in samples collected from sediments that were impacted by agricultural activities, while ciprofloxacin and erythromycin were prevalence from samples impacted by urban runoff. The high frequency with which resistant enterococci were found in selected locations within the watershed will provide useful information on pollutant types and sources affecting the Santa Ana River to the different water utilities agencies that will lead to the development of Best Management Practices for water quality improvements.

Review Publications
Ibekwe, A.M., Kennedy, A.C., Stubbs, T. 2010. An assessment of environmental conditions for control of downy brome by Pseudomonas fluorescens D7. International Journal of Environmental Technology and Management(IJETM). 12:27-46.

Leij, F.J., Bradford, S.A. 2009. Combined physical and chemical nonequilibrium transport model: Analytical solution, moments, and application to colloids. Journal of Contaminant Hydrology. 110(3-4)87-99.

Ibekwe, A.M., Poss, J.A., Grattan, S.R., Grieve, C.M., Suarez, D.L. 2010. Bacterial diversity in cucumber (Cucumis sativus) rhizosphere in response to salinity, soil pH and boron. Soil Biology and Biochemistry. 42(4):567-575.

Kim, H., Walker, S., Bradford, S.A. 2010. Macromolecule Mediated Transport and Retention of Escherichia coli O157:H7 in Saturated Porous Media. Water Research. 44(4):1082-1093.

Kim, H., Walker, S., Bradford, S.A. 2010. Coupled Factors Influencing the Transport and Retention of Cryptosporidium Parvum Oocysts in Saturated Porous Media. Water Research. 44(4):1213-1223.

Ibekwe, A.M., Grieve, C.M., Papiernik, S.K., Yang, C.H. 2009. Persistence of Escherichia coli 0157:H7 on the Rhizosphere and Phyllosphere of lettuce. Letters in Applied Microbiology. 49:784-790.

Kim, H.N., Hong, Y., Lee, I., Bradford, S.A., Walker, S.L. 2009. Surface Characteristics and Adhesion Behavior of Escherichia coli O157:H7: Role of Extracellular Macromolecules. Biomacromolecules. 10(9):2556-2564.

Bradford, S.A., Kim, H.N., Haznedaroglu, B.Z., Torkzaban, S., Walker, S.L. 2009. Coupled Factors Influencing Concentration Dependent Colloid Transport and Retention in Saturated Porous Media. Environmental Science and Technology. 43(18)6996-7002.

Last Modified: 4/20/2014
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