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primary amino acid sequence of their major protein subunits. The involvement of these other
types of fimbriae in biofilm formation has been studied, but to a much lesser extent (Van Houdt
and Michiels, 2005).
With regard to the other surface structures referred to in Table 3.1 , ompC and slp form outer
membrane proteins during the initial stages of biofilm formation (Sauer, 2003). Recently, Tabe
Eko Niba et al. (2007) demonstrated that mutants defective of surA were highly incapable of
forming biofilms, possibly due to the lack of initially attaching to abiotic surfaces.
A large amount of research has been devoted to understanding E. coli attachment to biotic
surfaces. In contrast, limited research has been devoted to understanding the mechanisms
involved in the initial attachment of E. coli transported in abiotic porous media, and the roles
these various surface structures described above, may play. Knowledge about these processes is
vital when making assessments of the suitability of using E. coli as an indicator organism for
specific pathogenic microorganisms in groundwater, for modeling and understanding the
movement of E. coli in the subsurface, or, more in general, for the application and injection of
bacteria in bioremediation studies. A good example of a more recent study was carried out by
Walker et al. (2004), who looked at the influence of LPS composition on cell adhesion. These
authors conclude that a complex combination of cell surface charge heterogeneity and LPS
composition is in control of the adhesive characteristics of E. coli K12. Lutterodt et al. (2009a)
studied the transport of 6 E. coli strains in 5 m columns of saturated quartz sand. These authors
conclude that Ag43 and motility play an important role in E. coli attachment to quartz grain
surfaces. In addition, they found that attachment efficiencies reduced with transport distance, and
these reductions were possibly related to motility variations and Ag43 expression variations
within an E. coli population. Finally, Bolster et al. (2009) show that there is a large diversity in
cell properties and transport behavior for the 12 different E. coli isolates they used. With the
parameters they used to characterize the E. coli surface (electrophoretic mobility, cell size and
shape, hydrophobicity, charge density, and extracellular polymeric substance composition), they
were not able to explain E. coli attachment variations.
The objective of this research was to establish the effects of variations in surface characteristics
of the outer membrane of E. coli on the attachment efficiency of 54 E. coli strains upon transport
in saturated quartz sand under identical flow conditions. In addition, we attempted to determine
which of these genes encoding those structures at the E. coli surface were likely related to the
initial attachment of the strains we used.
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