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distribution within bio-colloid populations and inter-strain attachment differences for different
E.
coli
strains under given physico-chemical transport conditions. However, all studies, aimed at
revealing sticking efficiency distributions, have been conducted for limited transport distances
(centimeter to decimeter), and can therefore not be considered representative for longer transport
distances, which are so important in microbial risk assessment of groundwater and therefore in
quantifying the potential health impacts of pathogenic microorganisms traveling in aquifers. In
addition, experiments that focussed on studying the effects of cell properties on their attachment
to quartz grains have been conducted at short transport distances (<0.5 m) for limited number of
strains (< 20 strains) (Becker et al., 2004, Bolster et al., 2010, Levy et al., 2007). Important
questions still remaining are: How low can the sticking efficiency of fractions of cells within a
population be? What are the effects of cell properties over long transport distances? And, how
wide can the inter-strain attachment variability among substantial numbers (>20 strains) of
different
E. coli
strains be? The objectives of this research were to:
•
Study the inter-strain attachment variability for substantial (>20) numbers of
E. coli
strains, the effects of their phenotypic properties and genes encoding the outer membrane
of
E. coli
cells on their attachment to quartz sand.
•
Study the intra-strain attachment heterogeneities of
E. coli
strains, the distribution of
sticking efficiencies over long transport distances (up to 25 m) and to measure low
sticking efficiency values, that can be considered environmentally realistic. In addition,
this study develops a methodology to measure the minimum sticking efficiency within
E.
coli
sub-populations.
•
Characterize the transport of
E. coli
strains isolated from springs, when considerable
transport through different aquifers has already taken place. The underlying hypothesis
was that transport by such a group of
E. coli
strains could possibly be characterized by a
rather homogeneous set of strain characteristics and transport parameters.
1.6. Thesis outline
The first part of the thesis looks at the effects of
E. coli
cell properties on their transport in
saturated porous media and consists of two
chapters (2
and
3)
. In
chapter 2
, the effects of
phenotypic characteristics (motility, hydrophobicity, outer surface potential and cell sphericity)
of
E. coli
strains and an outer membrane protein (Antigen-43) on their attachment to quartz
grains was studied over distances up to 5 m. In
Chapter 3
, inter-strain attachment differences
amongst various
E. coli
strains (from soils and different parts of zoo animals) over 7 cm was
studied. Furthermore, the effects of phenotypic characteristics and genes encoding 22 outer
membrane structures of
E. coli
on attachment to quartz grains were investigated.
To measure environmentally realistic low sticking efficiencies and to develop a methodology to
estimate the low values of bacteria attachment efficiency within bacterial sub-populations,
Part II
of the thesis focuses on the development of a methodology to determine the minimum sticking
efficiency of
E. coli
strains, and it involves intra-strain attachment variations and distributions in
E. coli
cell affinity for quartz grain surfaces. In this second part, transport experiments were
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