Environmental Engineering Reference
In-Depth Information
7.3.7 Chemotactic Index (C.I.)
A chemotaxis index parameter has been reported [25] to compare the chemo-
tactic response of different species to the same attractant. In a capillary assay
experiment, C.I. is defined as the ratio of the number of cells accumulated in the
capillary with attractant to that in the control.
7.4 Chemotaxis Transport Parameters
To evaluate the potential applicability of chemotaxis to in situ bioremediation of
environmental pollutants in soil and ground water, it is important to quantify this
process in terms of quantifiable chemotactic transport parameters that can be
directly incorporated into comprehensive bacterial fate and transport models.
Ford andHarvey [8] have recently presented a systematic approach for quantifica-
tion of these response parameters for laboratory-scale studies. This section pre-
sents a review of the transport parameters commonly reported in the literature.
7.4.1 Chemotaxis Sensitivity Coefficient (
0
)
The chemotactic sensitivity coefficient,
0
is an intrinsic cell population-based
parameter that theoretically relates the individual swimming behavior of a
bacterium to the resulting migration of the bacterial population [28]. This
parameter accounts for the mechanism by which bacteria respond to chemical
gradients. Ford and Lauffenburger [28] derived the following analytical expres-
sion for determining the chemotactic sensitivity coefficient for commonly used
capillary assay experiments:
0
¼
p
ð
1
þ
C
0
Þ
2
ð
C
1
C
0
Þ
N
N
RM
D
0
1
(7
:
3)
where D is attractant diffusivity; C
0
and C
1
are normalized attractant concen-
trations at the mouth and far end of the capillary, respectively. Concentrations
are normalized by the chemotaxis receptor constant, K
d
(defined later); N and
N
RM
are numbers of cells accumulated in the capillary in the presence and
absence of chemoattractant, respectively; and m
0
is the cell random motility
coefficient derived by Segel et al. [29]:
2
0
¼
p
4t
N
RM
pr
2
b
c
(7
:
4)
where N
RM
is the number of cells accumulated in a capillary of radius r at time t
and b
c
is the initial bacterial cell concentration in the chamber.
