Environmental Engineering Reference
In-Depth Information
reinforce the hypothesis that a correlation between chemotaxis and biodegra-
dation exists.
7.5.4 Chemotaxis Toward Chlorinated Compounds
Both aliphatic and aromatic chlorinated hydrocarbons are of growing concern
in the environment due to their abundant use as herbicides, pesticides, and
solvents in various industries [38]. Dichloroethylene (DCE), trichloroethylene
(TCE) and perchloroethylene (PCE) are common pollutants in the environment
and most of them are recalcitrant to biodegradation [38].
Some bacterial strains that are chemotactic toward chlorinated compounds
have been isolated for the biodegradation of chlorinated compounds (Table 7.2).
A chemotactic response toward 2,4-dichlorophenoxyacetate (2,4-D) is induced in
R. eutropha JMP123(pJP4) when grown on 2,4-D, which encodes the pJP4
plasmid containing genes for 2,4-D degradation [5]. P. putida PRS2000 exhibits
chemotaxis to 3- and 4-chlorobenzoate, when induced with 4-hydroxybenzoate
[38, 39]. P. putida F1, grown on toluene, is chemotactic toward TCE, DCE, PCE,
and other chlorinated compounds [20].
A review of the molecular basis of chemotaxis toward different pollutants
indicates that chemoreceptor genes are located within biodegradation gene
clusters and are coordinately regulated with these genes [5, 7]. In cases, where
the chemoreceptor has not yet been identified, chemotaxis toward different
pollutants is induced by growing on the pollutant itself or one of its metabo-
lites, which likely encodes the necessary chemoreceptors. Thus, it has been
speculated that chemotaxis may be an integral feature of the biodegradation
process [5, 7].
Genetic improvement of microorganisms has been suggested as an option for
environmental restoration [40]. Identification, isolation, and characterization
of chemotactic bacteria coupled with genetically improved degradation ability
may have great potential in optimization of in situ bioremediation.
7.6 Quantification of Chemotaxis for Bioremediation
Both experimental and modeling approaches for quantification of chemotaxis
with respect to bioremediation enhancement are described in the literature
[21, 31, 41, 42, 43, 44, 45, 46, 47] and will be presented in this section.
7.6.1 Quantification of Chemotaxis in Bulk Liquids
Marx and Aitken [44] evaluated naphthalene degradation by P. putida G7 in a
typical capillary assay experiment. Experimental data were fitted to a model in
