adapted
competent
required to evaluate the likely success of
microbes and nutrients. Microorganisms
intrinsic remediation; the bioavailability
from Geobacteraceae family due to their
of contaminants, levels of nutrients, the
physiological characteristics can play an
presence of minerals to buffer the pH of
important role in the bioremediation of
the matrix, adequate levels of electron
subsurface environments contaminated
acceptors (either oxygen, nitrate, ferric
with organic or metal contaminants
iron, or sulphate), and site specific
(Lovley et al., 2004). In some instances,
contamination
migration rates. This
the rate of biological degradation can be
approach deals with stimulation of
increased
through
the
addition
of
indigenous
or
naturally
occurring
microorganisms that have been shown to
microbial populations by feeding them
degrade the contaminants of concern at
nutrients and oxygen to increase their
high rates or are particularly well suited to
metabolic activity.
remain active under prevailing site
conditions. This process is referred to as
5. Microbes involved in bioremediation
bio augmentation. This can be useful if
the
contaminants
are
particularly
Microorganisms are responsible
recalcitrant to degradation or if site
for biodegradation in various diverse
conditions are extreme (for example: high
environmental
conditions.
These
concentrations
or
toxicity
of
microorganisms include: Acinethobacter,
contaminants). To be effective, the
Actinobacter, Acaligenes, Arthrobacter,
introduced organism(s) must become
Bacillins, Berijerinckia, Flavobacterium,
distributed throughout the contaminated
Methylosinus,
Mycrobacterium,
matrix and compete with the indigenous
Mycococcus, Nitrosomonas, Nocardia,
microorganisms for available nutrients. If
Penicillium,
Phanerochaete,
they are not distributed throughout the
Pseudomonas,
Rhizoctomia,
Serratio,
matrix the positive effect will be
Trametes and Xanthofacter. Individual
localized. On the other hand if the
microorganisms are not efficient in
introduced organisms compete poorly,
mineralization of harmful substances.
they will not persist and the treatment
Thorough mineralization results in a
effect will be short lived. The problems
progressive degradation by a group of
encountered using this approach include
microorganisms
(or
microbial
biofouling of equipment, injection wells
consortiums) and involves coaction and
and seepage beds. Adjustments to the
co-metabolism actions. Microorganisms
system, such as the use of new discharge
in various habitats have remarkable
areas, may be required to prevent this
physiological flexibility, so they are able
from
occurring.
This
approach
to
to make use of and often mineralize an
bioremediation must be evaluated on a
enormous number of organic molecules.
site specific basis.
Several other requirements for microbial
growth in biodegradation process are
4.12. Intrinsic bioremediation
listed in Table 2. Some microbes with
Often bioremediation can be
specific biodegradation capabilities are
accomplished without human intervention
discussed below.
by microorganisms that are naturally
Pseudomonas putida: In context
found in the contaminated matrix. For
of bioremediation, it is a microorganism
this approach to be used, it is usually
found in farmland soil involving high
necessary for the rate of contaminant
impact
xenobiotics
including
degradation to exceed the rate of
organophosphate insecticides, petroleum
contaminant migration. Knowledge of the
hydrocarbons, and both monocyclic and
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Table 2: Requirements for microbial growth in bioremediation process (Source: Vidali,
Requirement
Description
Nutrients
The growth and activity of the microorganisms must be estimated by adequate
maintenance and supply of nutrients. These nutrients are the basic building
blocks of life and allow microbes to create the necessary enzymes to break down
the contaminants. Bio-stimulation usually involves the addition of nutrients and
oxygen to help native microorganisms. Nitrogen (ammonic, nitrate, or organic
nitrogen) and phosphorous (orthophosphate or organic phosphorous) are
commonly used as the limiting nutrients. In certain anaerobic systems, the use of
trace metals (e.g. iron, nickel, cobalt, molybdenum and zinc) is generally
preferred.
Carbon source
Carbon which is considered as the most basic element of living forms is required
in larger quantities than other elements. Carbon contained in many organic
contaminants may function as a carbon source for cell growth. If the organism
involved is an autotroph CO2 or HCO3 in solution is required. In some cases,
contaminant levels are too low to supply suitable levels of carbon to cell. In these
cases the addition of carbon sources may be required.
Electron
All respiring bacteria require a terminal electron acceptor. In some cases, the
acceptor
organic contaminant may serve in this capacity. The most common electron
acceptor in aerobic bioremediation processes is dissolved oxygen. Under
anaerobic conditions, NO3-, SO 3-
4 , Fe3+, and CO2 may serve as terminal electron
acceptors. Certain co-metabolic changes are carried out by fermentative and other
anaerobic organisms, in which terminal electron acceptors are not necessary.
Energy source
In the case of primary metabolism, the organic contaminant supplies energy
required for growth. This is not the case when the contaminant is metabolized
via secondary metabolism or co-metabolism or as a terminal electron acceptor. If
the contaminant does not serve as a source of energy, the addition of a primary
substrate(s) is required.
Soil moisture
Microbial growth and activity is also affected by moisture content. The water-
holding capacity suggested for bioremediation process may range from 25% –
28%.
Temperature
Temperature regulates the rates of growth and metabolic activity. Surface soils
are particularly susceptible to wide variations in temperature. Generally,
mesophilic conditions are appropriate for most applications (with composting
being a notable exception).
pH
A pH is another important factor that affects bioremediation process. If the soil is
acidic, it is possible to raise pH by adding lime. A pH fluctuating between 6.5
and 7.5 is generally considered optimal. The pH of most ground water (8.0–8.5)
is not considered inhibitory.
Absence of
Many contaminated sites contain a mixture of chemicals, organic and inorganic,
toxic metals
which may be inhibitory or toxic to microorganisms. Heavy metals and phenolic
compounds are of particular concerns.
Adequate
For contaminants to be available for microbial uptake it must be present in
contact
aqueous phase. Thus contaminants that exist as non-aqueous phase liquids or are
between
sequestered within a solid phase may not be readily metabolized. For degradation
microorganisms it is necessary that bacteria and the contaminants be in contact. This is not easily
and substrates
achieved, as neither the microbes nor contaminants are uniformly spread in the
soil. It is possible to develop the mobilization of the contaminant utilizing some
surfactants such as sodium dodecyl sulphate (SDS).
Time
Time is an important factor in the start-up of bioremediation systems. Even the
above mentioned parameters are met, lag phases are often observed prior to the
onset of activity. In some cases, the intense bacterial population shifts that are
required for bioremediation will increase periods of slow activity.
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Bioremediation: A Biotechnology Tool for Sustainability Chandra et al.
polycyclic aromatics (Iyer and Damania,
organisms like bacteria, plant, virus or
animal and thus these are also referred to
Dechloromonas aromatic: This
as transgenic organisms (Ozcan et al.,
bacterium is involved in degradation of
aromatic compounds like benzene in
nitrate reducing conditions as well as
6.1. Role of GMOs in environmental
physiological
and
molecular
management
characterization in anaerobic mixed
Genetically modified organisms
cultures (Ulrich and Edwards, 2003).
can be used to clean up the environment
Deinococcus radiodurans – In
by bioremediation. Effects of some
field of development of bioremediation
genetically modified microorganisms are
strategies, this bacterium plays a role as a
unstable and vary according to species,
radiation resistant organism. It is used for
changes in population structure and loss
the treatment of mixed radioactive wastes
of some functions, to the formation of
containing ionic mercury (Brim et al.,
toxic metabolites. Presence of high and
2000). The radioactive waste sites can be
active microorganisms makes the process
treatedby this strategy of bioremediation.
of bioremediation more operative and
Methylibium
petroleiphilum
–
they must adapt with the changing
Also known as PM1 strain that is
environmental conditions. Deinococcus
involved in methyl tert butyl ether
radiodurans
that
exhibit
toluene
(MTBE)
bioremediation.
MTBE
is
dioxygenase to clear-out toxic elements
degraded by this strain using the
that are found in radioactive waste sites
contaminants as source of carbon and
was used by Lange (1998) as a
energy (Hanson et al., 1999).
recombinant. Deinococcus radiodurans is
Alcanivorax borkumensis is a rod-
known to have two properties, first it is
shaped bacterium having capability of
resistant to radiation and secondly it can
consuming hydrocarbons and produces
degrade chlorobenzene in radioactive
carbon dioxide. Hence it can be used
environments (Lange et al., 1998). Then
readily in oil damaged environment
again, it can only be produced in an
environment at temperatures less than
Phanerochaete chrysosporium – It
39°C and as radioactive sites generally
is the first fungi involved in degradation
have high temperatures, so a bacterium is
of organic pollutants (Kadri et al., 2017).
required that can function at higher
temperatures.
Another
well-known
6. Genetically modified organisms
example for the application of GMOs in
the management of environmental issues
Bioremediation by means of
can be cited through certain bacteria that
microorganisms is not significant for
can yield biodegradable plastics and this
treatment of all types of pollutants. For
quality of bacteria were transferred to
example, heavy metals such as cadmium
microbes which were cultured in the
and lead are not freely absorbed or taken
laboratory and now a days they have
by organisms. The role of genetically
enabled the wide scale greening of plastic
modified organisms in the process of
industry.
bioremediation has emerged as a new tool
In the early 1990s, Zeneca, a
(Jafari et al., 2013). A genetically
British
company,
established
a
modified organism, or GMO, is an
microbially manufactured biodegradable
organism that has an altered DNA
plastic
called
Biopol
configuration made through genetic
(polyhydroxyalkanoate, or PHA). The
engineering. Most of the genetically
plastic was made using a GM bacterium,
modified
organisms
have
been
Ralstonia eutropha, to transform glucose
transformed with DNA from other
and a variety of organic acids into a
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Bioremediation: A Biotechnology Tool for Sustainability Chandra et al.
flexible polymer (Perez-Pantoja et al.,
environment. Bioremediation is one of the
2008). GMOs which are able to
emerging biological strategies which is
metabolize oil and heavy metals through
applicable to the repair of damaged
their bacterially encoded ability may
environment.
prove effective for the bioremediation
The three main types of pollution
process.
Simultaneously,
genetically
(Soil, water and marine pollution) that are
engineered microorganisms (GEMs) have
controlled by bioremediation using a
shown possible uses for bioremediation in
variety of microorganisms which belong
soil, groundwater, and activated sludge
to different environments and are active
environments, due to the enriched
members of microbial associations are
degradative capabilities for extensive
discussed here.
range of contaminants. Recent advances
in molecular biology have unlocked new
7.1. Marine pollution
perceptions for the development of
The derivatives of petroleum are
engineering microorganisms with the
the most important source of energy for
purpose
of
performing
specific
industry and societies. The probable cause
bioremediation.
of oil spills in marine environment is
From the biological safety view it
mainly through the frequent transport of
has also been reported that not all
petroleum across the world. Moreover, it
naturally occurring bacteria are ideal as
is
broadly
known
that
petroleum
bioremediation agents. For instance,
hydrocarbons pollution has obstructed,
Burkholderia cepacia would be both used
and spoiled the world oceans, seas and
as an agent for bioremediation and for
coastal zones and due to this, the Earth‟s
biological regulator of phytopathogens.
health sustainability is at high risk. In
However, it causes cystic fibrosis in
marine environment too, bioremediation
humans and it is also found to be resistant
is considered as an economic and
to many antibiotics (Holmes et al., 1998).
ecological biotechnology tool for the
For these reasons, the US Environmental
handling of polluted wastes (Paniagua-
Protection Agency (EPA) has led to its
The
elimination
to
be
used
as
an
frequently
applied
bioremediation
environmental agent (Davison, 2005).
methods that can be used in marine
environments facing disturbance due to
7. Types of pollution controlled by
oil spills are (i) using the process of bio
bioremediation
augmentation by the addition of oil
degrading bacteria so as to grow or
The population explosion throughout the
improve the existing bacterial biota, and
world has led to an increase in the
(ii) use of composts (nutrients), to
polluted soil and water regions. As the
encourage and stimulate the growth of
number of people continues increasing
native oil degraders, which is called bio-
day by day it also results in the overuse of
stimulation. In the case of oil spills, the
natural resource like air, water and land
processes make use of the catabolic skill
resources. For these reasons, there occurs
of microorganism feeding on oil. Several
rapid expansion of industries, food, health
workers (Odu, 1978; Sloan, 1987; Ijah
care, vehicles, etc. but it is very
and Antai, 1988; Okpokwasili and
challenging to retain the quality of life
Okorie, 1988; Barnhart and Meyers,
with all these new expansions, which are
1989; Anon, 1990; Pritchard, 1991;
critical to the environment in which we
Pritchard and Costa, 1991; Hoyle, 1992;
live. Since the quality of life is very much
Ijah, 2002; and Ijah, 2003) have
linked to the overall quality of the
pronounced numerous application of
environment, worldwide measures are
microorganism in the bioremediation of
taken to sustain and preserve the
oil pollution with promising results.
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Bioremediation: A Biotechnology Tool for Sustainability Chandra et al.
7.2. Water pollution
dibenzodioxins
(PCDD),
and
Water pollution is a subject of
polychlorinated dibenzofurans (PCDF)
great global concern, and it can be largely
(Koning et al., 2000). The biological
distributed into three main groups, that is,
processes of ex situ remediation involve:
contamination by organic compounds,
composting, landfarming, biopiling and
inorganic
compounds
(e.g.,
heavy
the use of bioreactors. Alternatively,
metals),