Biology Reference
In-Depth Information
Abstract
To help improve the prediction of bacteria travel distances in aquifers laboratory experiments
were conducted to measure the distant dependent sticking efficiencies of two low attaching
Escherichia coli
strains (UCFL-94 and UCFL-131). The experimental set up consisted of a 25 m
long helical column with a diameter of 3.2 cm packed with 99.1 % pure-quartz sand saturated
with a solution of magnesium sulfate and calcium chloride. Bacteria mass breakthrough at
sampling distances ranging from 6 to 25.65 m were observed to quantify bacteria attachment
over total transport distances ( Α
L
) and sticking efficiencies at large intra-column segments ( Α)
(> 5 m). Fractions of cells retained (
F
) in a column segment as a function of Α were fitted with
a power-law distribution from which the minimum sticking efficiency defined as the sticking
efficiency of 0.001% bacteria fraction of the total input mass retained that results in a 5 log
removal were extrapolated. Low values of Α in the order 10
-4
and 10
-3
were obtained for
UCFL-94 and UCFL-131 respectively, while Α-values ranged between 10
-6
to 10
-3
for UCFL-94
and 10
-5
to 10
-4
for UCFL-131. In addition, both Α
L
and Α reduced with increasing transport
distance, and high coefficients of determination (0.99) were obtained for power-law distributions
of Α for the two strains. Minimum sticking efficiencies extrapolated were 10
-7
and 10
-8
for
UCFL-94 and UCFL-131, respectively. Fractions of cells exiting the column were 0.19 and 0.87
for UCFL-94 and UCL-131, respectively. We concluded that environmentally realistic sticking
efficiency values in the order of 10
-4
and 10
-3
and much lower sticking efficiencies in the order
10
-5
are measurable in the laboratory, Also power-law distributions in sticking efficiencies
commonly observed for limited intra-column distances (< 2 m) are applicable at large transport
distances(> 6 m) in columns packed with quartz grains.
High fractions of bacteria populations
may possess the so-called minimum sticking efficiency, thus expressing their ability to be
transported over distances longer than what might be predicted using measured sticking
efficiencies from experiments with both short (<1 m) and long columns (> 25 m). Also variable
values of sticking efficiencies within and among the strains show heterogeneities possibly due to
variations in cell surface characteristics of the strains. The low sticking efficiency values
measured expresses the importance of the long columns used in the experiments and the lower
values of extrapolated minimum sticking efficiencies makes the method a valuable tool in
delineating protection areas in real-world scenarios.
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