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observed by other workers (Lutterodt et al., 2009a, b Tufenkji and Elimelech, 2005b, 2004b,
Simoni et al., 1998, Baygents et al., 1998). The low sticking efficiency values obtained in this
work express the importance of the use of sufficiently long columns in bacterial transport
studies, as the possibility of obtaining these values is not possible with short columns. Note that
most values measured in laboratory setups reported in the literature range between 0.02 to 0.9
(Foppen and Schijven, 2006), and in some cases values greater than 1 were measured (Lutterodt
et al., 2009a,b, Paramanova et al., 2006, Morrow et al, 2005, Shellenberger et al., 2002). These
values are 2 to 5 orders of magnitude higher than results obtained in this work. The overall very
low Α
L
values (in the order of 10
-4
to 10
-3
) we obtained are only comparable to the lower limits
of reported field values (0.002-0.2; Foppen and Schijven, 2006). To our knowledge segment
sticking efficiency ( Α) values as low as 8.22×10
-6
obtained for UCFL-131 have not been
reported in literature. Actual sticking efficiency values in the environment can even be much
lower due to the ubiquitous presence of structural discontinuities and dissolved organic matters
which are known to enhance particle transport in aquifers.
The differences in Α
and Α
L
measured for both strains confirm the intra-population and inter-
population heterogeneities reported by other workers (Foppen et al., 2010; Bolster et al., 2009;
Bolster et al., 2000, Baygents et al., 1998, Simoni et al., 1998, Tong and Johnson, 2007). The
observed high values of both Α
L
and Α at comparatively short distances of transport from the
influent end of the column and decreasing with increasing transport distance is a phenomenon
that has commonly been attributed to the removal of highly attaching cell fractions within
bacterial populations (Lutterodt et al., 2009a,b, Foppen et al., 2007, Li et al., 2004, Albinger et
al., 1994, Bolster et al., 1999, 2000) and can be explained by the variation in cell surface
properties. A previous test for cell auto aggregation ability within the two strains under similar
growth and hydrochemical conditions showed very low aggregation ability (<5 %) (Foppen et
al., 2010). Therefore, the contribution of cell autoaggregation to the high sticking efficiency
recorded at short transport distances was ruled out. Until now no cell property has been proved to
convincingly influence
E. coli
attachment to quartz grains though cell motility and an auto
transporter protein, Antigen-43 (Ag43) have been proved to influence cell attachment to quartz
grains (Lutterodt et al., 2009a At equivalent transport distances the 5 times higher attachment of
UCFL-94 than UCFL-131 may possibly be due to differences in cell properties that influence
transport or attachment within the two strains. Previous work with these strains (Foppen et al.,
2010, Lutterodt et al., 2009a, Yang, 2005) indicated differences in various cell properties (i.e.
Ag43 expression, motility, outer surface potential, aggregation, cell size and sphericity) within
and among the strains. For Α, though the column segments were similar in length (6-6.85 m)
considering the total length of the columns (>25 m), values varied indicating that Α is not
segment length dependent but dependent on total distance of transport. This observation is
supported by the low correlation between
Αand
L
i
(data not shown).
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