Environmental Engineering Reference
In-Depth Information
fertilizers indicate that rapid release is detrimen-
tal to the sustenance of microbes in the long run,
and very slow release rates are unsuitable for
maintenance of rapid biodegradation rates. The
challenge that still remains is to design a slow-
release fertilizer whose release rates can be con-
trolled to allow optimal nutrient concentrations
over longer periods of time in the marine envi-
ronment (Nikolopoulou and Kalogerakis
2009
).
Some other exciting alternatives are: use
of nitrogen-fixing, hydrocarbon-oxidizers and
uric acid as a natural fertilizer. Nitrogen being
a limiting factor in biodegradation following an
oil spill, a strong selection for nitrogen-fixing,
hydrocarbon-oxidizers is important. However,
few reports exist that unequivocally demonstrate
nitrogen fixation coupled with growth on hydro-
carbons larger than ethane. Consortia of bacteria
degrading hydrocarbon through nitrogen fixation
have been reported (Foght
2010
).
Azotobacter
chroococcum
isolated from oil-polluted site is
currently the sole example of a marine nitrogen-
fixing, hydrocarbon-oxidizers microbe (Thavasi
et al.
2006
). Another option is addition of nutri-
ent amendments to the oil spill using thin-filmed
minerals comprised largely of Fuller's Earth
Clay. Together with adsorbed N and P fertilizers,
filming additives, and organoclay, clay flakes can
be engineered to float on seawater, attach to the
oil, and slowly release contained nutrients. Large
amount of oil is converted in bacterial biofilm
and there is significant reduction in alkane con-
tent (Warr et al.
2013
).
Studies on uric acid, a biostimulant, during
oil spill are rapidly gaining credence in scientific
circles. Uric acid has low solubility in water, has
adherence to hydrocarbons, is major nitrogen
waste in animals, and is readily available as inex-
pensive commercially available fertilizer, guano
(Ron and Rosenberg
2014
). Many bacterial spe-
cies including
Alcanivorax
strains have been
documented to use uric acid as a natural source
of nitrogen (Knezevich et al.
2006
). Uric acid has
been suggested as a potential biostimulant for
bioremediation of oil spills (Ron and Rosenberg
2014
).
augmentation. Of particular interest to bioaug-
mentation are groups of microbes that utilize
hydrocarbon as sole source of carbon and energy.
Such microbes are called hydrocarbonoclastic
bacteria. They include strains of
Alcanivorax
(Yakimov et al.
1998
; Kostka et al.
2011
),
Cyclo-
clasticus
(Dyksterhouse et al.
1995
),
Oleiphilus
(Golyshin et al.
2002
),
Oleispira
(Yakimov et al.
2003
),
Thalassolituus
(Yakimov et al.
2004
),
and
Planomicrobium
(Engelhardt et al.
2001
).
Alcanivorax
sp.
grows only on
n
-alkanes and
branched alkanes as carbon and energy source.
Similarly,
Cycloclasticus
strains grow on aro-
matic hydrocarbons such as naphthalene, phena-
nanthrene, and anthracene while
Oleiphilus
and
Oleispira sp.
grow on aliphatic hydrocarbons,
alkanoles and alkanoates (Head et al.
2006
).
The predominant growth of
Alcanivorax
after
biostimulation in oil-impacted marine environ-
ment has been shown by conventional methods
and also proved by 16S rRNA gene sequencing
studies (Syutsubo et al.
2001
; Roling et al.
2002
,
2004
). It has been suggested that growth is due to
the higher ability of this genus to use branched-
chain alkanes
. Alcanivorax borkumensis
relies
exclusively on alkanes as energy source, thus it is
unsurprising that it has multiple alkane-catabolism
pathways including alkane hydroxylases (AlkB1
and AlkB2) and 3 cytochrome P450-dependent
alkane monooxygenases (Schneiker et al.
2006
).
In cold marine environments,
Oleispira sp.
is the
dominant alkane-degrading microbe associated
with oil spills (Coulon et al.
2007
) rather than
Alcanicorax sp.
, whereas in temperate environ-
ments,
Thalassolituus
spp. are the dominant spe-
cies (McKew et al.
2007
). Generalists (microbes
capable of using alkanes and/or polyaromatic hy-
drocarbon as well as nonhydrocarbons) such as
Acinetobacter
(diverse array of alkane hydroxy-
lases capable of degrading wide array of short-
and long-chain alkanes is present)
, Roseobacter,
Marinobacter, Pseudomonos
, and
rhodococcus
sp.
are important constituents of hydrocarbon-
degrading community. Although
Cycloclasticus
sp.
is the leading polycyclic aromatic hydro-
carbon (PAH) degrader,
Vibrio, Marinobacter,
Microbacterium, Pseudoalteromonas, Halomo-
nas
, and others contribute significantly to PAH
degradation (McGenity et al.
2012
). In estuarine
Bioaugmentation
Seeding of microorganisms at the site of oil spill
Search WWH ::
Custom Search