Submitted to: International Agrophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2008
Publication Date: 3/30/2008
Citation: Pachepsky, Y.A., Karns, J.S., Yu, O., Shelton, D.R., Guber, A.K., Van Kessel, J.S. 2008. Strain-dependent variations in attachment of E. coli to soil particles of different sizes. International Agrophysics. 22:61-66. Interpretive Summary: Land-applied manures and animal waste on grazing lands may contain various pathogenic strains of Escherichia coli that cause water contamination and concomitant public health problems. Currently, the overall E.coli content in natural waters is used to evaluate the degree of fecal contamination. Movement of E. coli in the environment is strongly affected by its attachment to soil. It is not known whether the genetic makeup of pathogenic E. coli alters the ability of bacteria to attach to soil particles as compared with non-pathogenic E. coli. We used modern DNA extraction and analysis techniques to pose and answer a preliminary question: can we discern genetic effects on the attachment of different E. coli to soils and soil particles? Using DNA fingerprinting, we have shown that the genetic makeup of E. coli undoubtedly defines the affinity of particular strains to attach to soil particles of different sizes. Because the attachment to mineral surfaces may be different for pathogenic vs. nonpathogenic E. coli strains, more information on attachment pathogenic E. coli to suspended solids in overland flow attachment needs to be collected, as the differences in attachment may result in differences in overland transport of pathogenic and non-pathogenic E. coli.
Technical Abstract: Attachment of E. coli to soil particles affects the bacteria transport in overland flow and in soil. The objective of this research was to investigate the existence of strain-dependent variations in attachment of manure-borne E. coli to soil particles of different sizes using rep PCR techniques. The Tyler clay loam soil was fractionated to obtain particles of coarse sand, medium sand, fine sand, silt, and clay sizes. The aged manure was cultured with the goal of producing a uniform inoculum for attachment studies without selecting for any particular strains. Serial dilutions of the fecal coliform suspension were mixed with one gram of soil in 10 mL of water to obtain fecal coliform concentrations of 102 and 103 CFU mL-1. Fifty E. coli isolates for each soil fraction supernatant and 50 isolates representing the E. coli suspension without soil were utilized for the extraction of DNA to be used for polymerase chain reaction (PCR) using ERIC primers. The DNA fingerprint analysis was done with pseudo-gel images from electrophoregrams using BioNumerics. The DNA concentrations in the supernatants were on average about 90 ng 'L-1 and did not exhibit a significant dependence on soil particle size. The cluster analysis led to identification of five clusters with the similarity level within them higher than 80% and 17 clusters with the similarity level within them higher than 90%. The chi-square test was applied to test the hypothesis that the strain distribution among the clusters does not depend on adsorbent. This hypothesis could be rejected at 0.0001 probability level. The preferential attachment of different strains to particles of different size classes may be attributable to differences in both particle surface properties. It remains to be seen whether the attachment to mineral surfaces for pathogenic E. coli strains may be different from that for non-pathogenic strains.