Effects of surface characteristics on the transport of multiple Escherichia coli isolates in large scale columns of quartz sand - Transport of Multiple Escherichia Coli Transport in Saturated Porous Media - page 16

2.3 Results

2.3.1 Surface Properties

Average cell width for the strains ranged from 0.84 to 1.09 m with a standard deviation (SD) of
0.09 m, and the average length ranged from 1.76 to 2.42 m (SD = 0.22 m). The equivalent
spherical diameter ( Table 2.1 ) of the cells ranged from 1.33 to 1.53 m (SD = 0.10 m), while
the cell sphericity ranged from 0.40-0.57 (SD = 0.07 m). From this we concluded that the cell
dimensions of all isolates used were within a relatively narrow range. The motility of the cells
showed considerable variation (SD = 1.31 cm): while the diameter of the UCFL-167 colony on
the soft agar plates was only 0.36 cm, the diameter of the UCFL-131 colony was 3.73 cm.
Although not exactly similar, these variations had similar ranges as the variations measured by
Yang (2005).

Table 2.1: Measured surface properties and Ag43 expression

Strain ESD* Sphericity Motility Hydrophobicity Zeta potential Decay rate Ag43

(hr -1 ) (µm) (W/L) (cm) (% partitioning) (-mV) expression**

DI AGW DI AGW DI AGW

UCFL-71 1.34 0.48 2.40 27.33 33.36 44.76 25.06 0.05 0.03 0

UCFL-94 1.45 0.54 0.57 22.12 44.80 54.74 17.89 0.01 0.00 1

UCFL-131 1.53 0.40 3.73 36.57 38.06 47.95 15.76 0.12 0.03 2

UCFL-167 1.30 0.42 0.36 81.01 55.96 31.79 23.91 0.02 0.01 1

UCFL-263 1.33 0.57 1.73 59.99 46.03 53.38 19.19 0.11 0.00 3

UCFL-348 1.53 0.51 2.77 35.37 53.45 49.36 24.30 0.07 0.01 3

*: ESD = Equivalent Spherical Diameter
**: 0: negative; 1: very few positive cells in a population; 2: positive; 3: positive, significant
aggregates

The hydrophobicities varied from 22% (UCFL-94) to 81% (UCFL-167) in DI water (SD = 22 %)
and from 33 to 55% in AGW (SD = 9 %). Four out of six strains (UCFL-71, UCFL-94, UCFL-
131 and UCFL-348) were more hydrophobic in AGW than in DI water. The OSP ranged from -
32 mV to -55 mV in DI water (SD = 8.3 mV) and from -14 mV to -22 mV in AGW (SD = 3.4
mV), so in all cases, the cells were negatively charged, while the less negative charge of the cells
in AGW was explained by the compressed double layer due to the relatively high ionic strength
compared to DI .