Biology Reference
In-Depth Information
Abstract
We hypothesized that the transport of
E. coli
strains harvested from termination points of
flow lines in aquifers (e.g. springs) could possibly be characterized by a rather homogeneous
set of
E. coli
surface characteristics and transport parameters. In order to test our hypothesis,
we sampled 77 springs throughout the Lubigi catchment, which is part of Kampala, the
capital of Uganda. Of the spring water samples, besides chemical and physical parameters,
also thermotolerant coliform concentrations were determined. Furthermore,
E. coli
strains
were harvested, and cell properties (serotype, hydrophobicity, motility, zeta potential, cell
aggregation, and cell size) were determined. Then, of 40 randomly selected
E. coli
strains
transport experiments in saturated quartz columns of 7 cm height were carried out to
determine transport characteristics of the strains. Using a two-site non-equilibrium sorption
model, transport was modeled with HYDRUS 1-D, and fitted with measured breakthrough
data. The results demonstrated fecal contamination of the springs with high thermotolerant
coliform concentrations and also high concentrations of chloride and nitrate. The transport of
the
E. coli
strains was remarkable similar: some 82 % of the strains had a maximum relative
breakthrough concentration between 0.5 and 1, while some 75% of the 40 strains had similar
attachment efficiency values in the order of 10
-3
and 10
-4
. We attributed this to the way in
which the strains were harvested: from springs, and therefore at the termination points of
flowlines. Such strains may indeed possess certain cell characteristics that might have
influenced their selective transport in the subsurface giving rise to their similar transport
characteristics in our columns. There was however no statistically significant correlation
between measured cell properties (serotype, zeta potential, motility, cell size, cell
aggregation, and hydrophobicity) and transport parameters (
f
,Ω
and
k
and (C/C
0
)
max
).
Furthermore, 58% of the strains we tested were of the O21:H7 serotype. This suggests that
this specific serotype may possess certain characteristics that allows its preferential transport
through the shallow aquifers, in the Kampala area. Our work demonstrated that in order to
assess transport characteristics of
Escherichia coli
in real world surroundings, it seems to be
better to harvest bacteria from the aquifer itself rather than from pollution sources, like fecal
sludge, solid waste piles or grey water disposal sites.
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