Environmental Engineering Reference
In-Depth Information
no
G.max
was planted (Njoku and Oboh
2009
).
In a study, Liu et al. found that typical ornamental
species including
Gaillardia aristata, Echinacea
purpurea,
Fawn (
Festuca arundinacea Schreb
),
Fire Phoenix (a combined
F. arundinacea
), and
Medicago sativa L.
can be adopted in the phy-
toremediation of oil-contaminated soil. Since
these do not enter the food chain and provide
ornamental cover to the revegetated land, they
can serve as better alternative than using crops
for phytoremediation of petroleum hydrocarbons
(Liu et al.
2012
). Phytoremediation might be
most effective during the vegetative growth stag-
es as greater abundance of hydrocarbon-degrad-
ing bacteria containing
alkB
and
tol
genes was
observed at these stages in the phytoremediating
species,
Phragmites australis
(Nie et al.
2011
). A
greater understanding of rhizosphere-associated
bacteria and need of bioaugmentation for
in situ
bolstering of hydrocarbon-degrading bacteria are
required to chart out potential candidates for the
phytoremediation of oil spills in wetlands and
coastal zones.
genes were able to convert phenanthrene, naph-
thalene, methylnaphthalene, dibenzofuran, and
dibenzothiophene to their hydroxylated forms.
Furthermore, these
E. coli
cells also transformed
biphenyl- and diphenylmethane, which are ordi-
narily the substrates of biphenyl dioxygenases
(Kasai et al.
2003
; Harayama et al.
2004
). Exhibi-
tion of such broad substrate specificity can make
Cycloclasticus
the key player in oil-contaminated
sea water (Harayama et al.
2004
). Bacteriophages
offer steady supply of nutrients needed for bac-
terial hydrocarbon degradation through phage-
mediated biomass turnover. Phages, together with
various mobile genetic elements, are also impor-
tant tool for dissemination of valuable genetic
material, including hydrocarbon-degradation
genes and the generation of new catabolic path-
ways via lateral gene transfer (Herrick et al.
1997
;
Top et al.
2002
). Thus, studies based on phage-
mediated gene transfer can also be targeted as po-
tential tool for transfer of genes into indigenous
species. PAH detoxification can also be achieved
by laccase enzyme. Taking this into account, lac-
case from
Myceliophthora thermophila
(MtL)
was successfully expressed in
Saccharomyces
cerevisiae
with the help of directed evolution
in an attempt to bioremediate petroleum spills
(Bulter et al.
2003
). Often, the role of GMOs in
bioremediation is considered as a lost cause due
to steep impediments in this field. However, as
Ananda Chakraborty says “oil spills are old love”
(Fox
2011
), this field is not dead yet; synthetic
biology approaches are being made to understand
the natural pathways better. Without this knowl-
edge, it is impossible to tweak the existing under-
performing metabolic pathways in the potential
candidates for bioremediation (Fox
2011
).
Role of genetically modified organisms
The use of GMOs, especially designed for petro-
leum hydrocarbon degradation, has been given
serious consideration. However, due to the com-
plex nature of oil and accompanied change in its
components due to weathering and multifaceted
and interconnected metabolic pathways integral
to degradation of petroleum hydrocarbon, this
field has remained in infancy. Moreover, GMOs
do not find public acceptance and there are only
few takers of such organisms. Regulatory bodies
across the world have strong reservations against
GMOs and the recent decline in funding of biore-
mediation research projects has also further im-
pacted this field (Fox
2011
). Thus, only few stud-
ies are currently available.
Cycloclasticus
strain
A5 is capable of growing on naphthalenes, diben-
zothiophenes, phenanthrenes, and fluorenes with
or without alkyl substitution. The genes encoding
the a and b subunits of an iron-sulfur protein, a
ferredoxin and a ferredoxin reductase, respec-
tively termed
phnA1
,
phnA2
,
phnA3
, and
phnA4
were isolated from it. Transformed
Escherichia
coli
cells containing the
phnA1
,
A2
,
A3
, and
A4
9.5
Perspective
The most crucial phase after an oil spill is the
first few days. Oil if not dispersed, reclaimed, or
evaporated, tends to sediment to the benthic re-
gion where it can remain for decades. Therefore,
it is imperative that resources, norms, and logis-
tics necessary for the
in situ
trial should be readi-
ly accessible to enable a quick decision to initiate
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