Bacterial, particulate, and environmental factors driving E. coli attachment

Liang, Xiao
Major Professor
Michelle Soupir
Michael Thompson
Committee Member
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Agricultural and Biosystems Engineering

Currently, 178,048 miles of impaired streams are contaminated due to elevated levels of pathogens or pathogen indicators. While attachment of bacteria to particulates is an important transport mode, understanding of the factors driving these interactions is lacking. Previous studies have indicated bacteria attachment to particulates is influenced by bacterial surface properties, particulate properties, and environmental conditions. The goal of this study was to explore bacterial, particulate, and environmental factors driving E. coli attachment to particulates in the aquatic environment. Specific objectives were: 1) to determine if differences in environmental E. coli cell surface properties are due to extrinsic (environmental) or intrinsic (genomic) properties, or an interaction of the two; 2) to identify the impacts from bacterial and particulate properties on E. coli attachment fractions by constructing statistical models; 3) to elucidate mechanisms of E. coli attachment to particulates in livestock manure.

Cell properties including hydrophobicity, zeta potential, net charge, total acidity, and EPS (extracellular polymeric substances) composition were measured for 77 genomically distinct E. coli strains collected from two environmental habitats (stream sediments and water). Meanwhile, attachment assays were constructed using a single E. coli strain and one model particulate (ferrihydrite, Ca-Montmorillonite, or corn stover) with environmentally relevant concentrations. Our results indicated variations between stream sediment E. coli and water E. coli in hydrophobicity, EPS protein and sugar content, net charge, and point of zero charge. The diversity of cell properties was due to interactions of extrinsic and intrinsic properties. Moreover, Generalized Additive Model (GAM) successfully predicted the attachment fractions to Ca-Montmorillonite and corn stover using cell characteristics as predictor variables and net charge had a linear impact on the attachment fractions.

Three genomically different beef manure E. coli strains (A, B and C) and one E. coli O157:H7 (ATCC 43888) were analyzed for their attachment to two types of beef manure particles with size smaller than 53 µm: methylene chloride insoluble and soluble. Flow cytometry was employed to measure attachment fractions for 6 different E. coli concentrations and the Freundlich isotherm successfully fitted the attachment data. The results indicated a more heterogeneous mechanism for E. coli attachment to methylene chloride manure particulates.