Biology Reference
In-Depth Information
fluid flow velocity (Darcy velocity) was maintained in all experiments. Short (7 cm) and long
(1.5 - 25 m) columns were used to investigate inter-strain attachment variations among the
strains, and multiple sampling distances along the lengths of the long columns were applied
to study intra-strain attachment differences, distributions in attachment efficiency within
E.
coli
strains and to develop a methodology to measure the minimum sticking efficiency, in
addition, the long column experiments were used to measure low values of the distance
dependent sticking efficiency. Cell properties, phenotypic characteristics (motility, average
cell size, cell aggregation, hydrophobicity and zeta potential) and genes encoding structures
at the outer membrane of
E. coli
cells were measured prior to experiments to investigate their
effects on transport/attachment.
8.2 Variability in
E. coli
transport, low values of sticking efficiencies and the minimum
sticking efficiency
Transport experiments in long columns with multiple sampling ports at increasing transport
distances helped in studying intra-strain attachment variations, distributions in sticking
efficiency and measuring low values of the distance dependent sticking efficiency of fractions
of cells within
E. coli
strains. In addition, two computational methods that make use of
relative bacteria mass breakthrough to quantify cell attachment (Abudalo et al., 2005,
Kretzschzmar et al., 1997) were applied. First, the entire transport distance from top
(influent) of the column to a sampling port was considered, and this allowed for the
comparison of transport of different
E. coli
strains at equal and increasing distances (
Chapters
2
and
4
to
6
). The second method involved the computation of sticking efficiency of cells
retained in a column segment (Martin et al., 1996), in between two sampling distances. In this
way, the sticking efficiency of fraction of total mass input retained in a segment could be
determined and distribution functions that best described the relation between the two
parameters were assessed (
Chapters 4
to
6
). Short column experiments were conducted for
strains isolated from zoo animals, soils of a pasture used for animal grazing (
Chapter 3
) and
for strains isolated from springs in the Kampala area in Uganda (
Chapter 7
).
The relation between fraction of cells retained in a column segment and corresponding
sticking efficiency was best described by a power-law (
Chapters 4
-
6
), though exponential
distribution was equally good (
Chapter 4
). In
chapters 4
and
5
, the minimum sticking
efficiency was introduced and defined as the sticking efficiency belonging to a bacteria
fraction of 0.001% of initial bacteria mass flowing into a column, after removal of 99.999%
(5 log reduction) of the original bacteria mass has taken place. This minimum sticking
efficiency was extrapolated from the power-law relation between segment sticking
efficiencies and mass fractions retained in segments. However, within this minor fraction of
bacteria cells, the sticking efficiencies were not a constant but distributed, and within this
0.001% sub-fraction, the minimum sticking efficiency is the
highest
possible sticking
efficiency.
From results obtained in all experiments, it was concluded that intra-strain and inter-strain
heterogeneities existed within and among the
E. coli
strains studied. Inter-strain attachment
variations were observed in all transport experiments conducted: In
chapter 3
,
E. coli
strains
isolated from soils and from feces and different parts of zoo animals showed a two log unit
variation in maximum breakthrough, whereas experiments with
E. coli
strains isolated after
transport through springs (
Chapter 7
) resulted in overall homogeneity. The majority of the
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