International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 193 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Rhizoremediation of pesticides: mechanism of microbial interaction in
mycorrhizosphere
Kriti Kumari Dubey * and M.H. Fulekar *#
*Environmental Biotechnology Laboratory, Department of Life Sciences, University of
Mumbai, Santacruz (E), Mumbai-400 098, India
#School of Environmental science and Sustainable Development, Central University of
Gujarat, Gandhinagar, Gujarat-482030,India
corresponding author: [email protected]: Tel: +91-2226528847, Fax: +91-
222652605
Abstract:
Rhizosphere bioremediation or rhizodegradation is the enhanced biodegradation of
recalcitrant organic pollutants by root-associated bacteria and fungi under the influence
of selected plant species. Use of selected vegetation and sound plant management
practices, increase the total proportion of pollutant degraders in numbers and activity
in the rhizosphere, leading to enhanced rhizodegradation of recalcitrant pesticides.
Pesticides are capable of persisting in the environment and causing concerns for human
health. The increasing costs and limited efficiency of traditional Physico-chemical
treatments of soil have spurred the development of new remediation technologies. The
use of plants and native microorganisms to degrade or remove pollutants has emerged
as a powerful technology for in situ remediation. An understanding of the mechanisms
of pollutant degradation in the rhizosphere environment is important for successful
implementation of this technology. Recent studies have demonstrated that plants and
rhizosphere associated microorganism produce pesticide-degrading enzymes that can
mineralize different groups of pesticides and their metabolites with greater efficiency.
Thus, rhizoremediation appears a very promising technology for the removal of
pesticides from polluted soil. The aim of present review is to provide improved
understanding of mechanism of microbial interaction in rhizosphere, which will help to
translate the results of simplified bench scale and pot experiments to the full complexity
and heterogeneity of field experiments with predictable remedial success.
Introduction:
Environmental pollution has become an increasing global concern. The modern
technological innovations, production and processes have generated wastes which
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 194 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
contain the complex inorganic and organic compounds. The treatment of the wastes has
become great concern to the environmentalists. Pesticides waste generated through
chemical processing in pesticide industry and their commercial, agricultural and
domestic usages have enhanced the level of hazardous environmental contaminants.
Pesticides wastes find their ways in soil-water causing environmental pollution.
Pesticides contamination in soils, surface water and ground water poses major
environmental problem worldwide. Environmental management of the pesticides has
become a major concern to the environmentalists. There is an urgent need to develop
cost- effective and sustainable technology to remove contaminants from the
environment or to detoxify them. Rhizoremediation and bioremediation has attracted
an increasing attention of scientists, industries and government agencies that are facing
the challenge of remediation and restoration of hazardous wastes. The recent advances
in remediation technology using microbial consortium and identified potential degrader
have been found effective for the treatment of pesticides in soil-water environment
(Fulekar, 2005). Rhizoremediation technology uses plant roots and associated microbial
consortium to degrade environmental pollutants/toxins from soil with an aim of
restoring area sites to a condition useable for intended purpose. Rhizoremediation
takes advantage of plant roots natural symbiosis with mycorrhiza and root associated
natural microbial flora for the enhanced degradation of pollutants in the rhizosphere.
Bioremediation techniques can be used to remove hazardous waste pesticides which
have already polluted the environment. In bioremediation microorganisms breakdown
most compounds for their growth and energy needs. Bioremediation and
phytoremediation are innovative technologies that have the potential to alleviate
pesticide contamination. The process of bioremediation usually occurs in soil, whereby
pesticides are broken down into less active/toxic compounds by fungi, bacteria, and
other microorganisms that use pesticides as energy and carbon sources. It is estimated
that 1 g of soil contains more than one hundred million bacteria (5000–7000 different
species) and more than ten thousand fungal colonies (Dindal, 1990; Melling, 1993). The
use of microbial metabolic potential for eliminating soil pollutants provides a safe and
economic alternative to other commonly used physico-chemical strategies (Vidali,
2001). Indigenous microorganisms (natural attenuation) can be used for detoxification
of contaminants in the environment. The application of in situ bioremediation with
naturally occurring microorganism has been revealed in scientific reports
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 195 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
(Bhupathiraju et al., 2002).Detoxification of pesticides by indigenous soil
microorganisms and/or enzymes isolated from microbes has been well explained in this
review article. Soil conditions strongly influence the effectiveness of bioremediation
(Morra, 1996; Riser-Roberts, 1998). The effects of soil moisture, temperature, aeration,
pH, and organic matter content on the biodegradation of pesticides have been
investigated in many studies (Bending et al., 2006; Charnay et al., 2005; Rasmussen et
al., 2005). Therefore, a brief section on soil factors affecting pesticide biodegradation
has also been included in this article. The aim of present review is to understand the
mechanism of rhizoremediation of pesticides in rhizosphere, with emphasis on certain
aspects of plant associated microbes with remediating potential of pesticides and their
relevant remediation efforts.
Mechanism of Pesticide Degradation in the Rhizosphere:
Chemicals released by plants may enhance xenobiotic degradation, and it may therefore
be beneficial to use plants in the remediation of contaminated soils. The term
“rhizosphere” describes the soil volume around plant roots, which is influenced by the
activities of the living roots. Rhizosphere is a complex environment that supports a huge
number of metabolically active microbial populations, several orders of magnitude
higher than the non-rhizospheric soil. The rhizosphere is the zone of soil around the
root in which microbes are influenced by the root system forming a dynamic root-soil
interface (Kuiper et al., 2004; Pilon-Smits, 2005; Barea et al., 2005).
There are three separate, but interacting, components recognized in the
rhizosphere:
1) Rhizosphere (soil): the zone of soil influenced by roots through the release of
substrates that affect microbial activity.
2) Rhizoplane: the root surface, including the strongly adhering soil particles.
3) Root tissue: that some endophytic microorganisms (endophytes) are able to colonize
(Barea et al., 2005).
The differing physical, chemical, and biological properties of the root-associated
soil, compared with those of the bulk soil, are responsible for changes in microbial
diversity and for increased numbers and metabolic activities of microorganisms in the
rhizosphere microenvironment, the phenomenon called the rhizosphere effect (Barea et
al., 2005; Kuiper et al., 2004; Pilon-Smits, 2005; Salt et al., 1998).
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 196 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Densities of rhizospheric bacteria can be as much as two to four orders of
magnitude greater than populations in the surrounding bulk soils and display a greater
range of metabolic capabilities, including the ability to degrade a number of recalcitrant
xenobiotics (Pilon-Smits, 2005; Salt et al., 1998). Therefore, to find an accelerated rate
of biodegradation of organic pollutants is found in vegetated soils compared with non-
vegetated soils. Rhizosphere effects on xenobiotic biotransformation have been studied
for a variety of compounds, although the mechanisms by which certain plants enhance
biodegradation are still poorly understood. Differences in plant tolerance to phytotoxic
compounds in soils may be related to the plants’ ability to induce microorganisms that
will detoxify these xenobiotics in the soil environment . Research on phytoremediation,
through trial and error, has focused on densely rooted, fast growing grasses and plants,
such as Brassica sp., with fine root systems. Mulberry (Morus alba L.) and poplar
(Populus deltoides) trees have been used successfully in the phytoremediation of
chlorophenols and chlorinated solvents such as trichloroethylene (TCE) (Stomp et al.
1993). Salicylic acid, flavonoids, and monoterpenes are structurally analogous to many
anthropogenic compounds in that they are small, mobile chemicals that are amenable to
cellular uptake and may interact through signal transduction pathways to induce the
production of specific degradative enzymes.
Phytoremediation is also a cost-effective and innovative technology that uses
plants to clean up a broad range of organic and inorganic wastes (Cunningham et al.,
1995; Licht & Isebrands, 2005; Salt et al., 1998). Plants can bioaccumulate xenobiotics
in their above-ground parts, which are then harvested for removal. Plants may
contribute to remediation in several ways, by reducing the leaching of contaminants,
aerating soil, phytodegradation/transformation, phytovolatilization,
evapotranspiration, and rhizoremediation (Amos & Younger, 2003; Chang et al., 2005;
Cunningham et al., 1995). The selection of bioremediation or phytoremediation for
cleanup of a contaminated site may depend upon prevailing conditions that support the
application of microbes, plants, and/or both. Without the microbial contribution,
phytoremediation alone may not be a viable technology for many hydrophobic organic
pollutants (Chaudhry et al., 2005). The use of rhizomicrobial populations present in the
rhizosphere of plants for bioremediation is referred to as Rhizoremediation ( Kuiper
et al., 2004). The term consists of both stimulation and rhizodegradation describing,
thus, the importance of both the plant and the microbes in this beneficial interaction.
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 197 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Table 1. Plant species shown to facilitate microbial degradation of pesticides in the
rhizosphere:
Plant
rhizosphere
Pesticide Summary Reference
Sugarcane 2,4-D High population of 2,4-D-
degrading microorganisms
in the rhizosphere of
sugarcane
Sandman and ,
Loos,1984
Rice Benthiocarb Eightfold increase in
heterotrophic bacteria in the
rhizosphere
Sato, 1989.
Corn Atrazine Increase in production of
atrazine degradation
Seibert et al., 1981
Kochia Atrazine,
metolachlor,
and
trifluralin
Increased mineralization
compared to
nonrhizosphere soils
Anderson et
al.(1994)
Zinnia
anguistifolia
Mefenoxam Pseudomonas fluorescens
and Chrysobacterium
indologenes
Pai et al.(2001)
Rye grass Chlorpyrifos Increased degradation in
rhizo-sphere soils
Korade and Fulekar
(2010)
Pennisetum
pedicellatum
Chlorpyrifos
Cypermethrin
Fenvalerate
Selective enrichment of
degraders in rhizosphere
soil
Dubey and Fulekar
(2011a)
Plant-microbial interactions in the rhizosphere offer very useful means for
remediating environments contaminated with recalcitrant organic compounds
(Chaudhry et al., 2005). Plant roots can act as a substitute for the tilling of soil to
incorporate additives (nutrients) and to improve aeration (Kuiper et al., 2004; Aprill &
Sims, 1990).Various grass varieties and leguminous plants have shown to be suitable for
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 198 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
rhizoremediation (Kuiper et al., 2001, 2004). The mucigel secreted by root cells, lost
root cap cells, the starvation of root cells, or the decay of complete roots provides
nutrients in the rhizosphere (Kuiper et al., 2004; Lynch & Whipps, 1990). In addition,
plants release a variety of photosynthesis derived organic compounds (Pilon-Smits,
2005; Salt et al., 1998). These root exudates contain water soluble, insoluble, and
volatile compounds including sugars, alcohols, amino acids, proteins, organic acids,
nucleotides, flavonones, phenolic compounds and certain enzymes (Chaudhry et al.,
2005; Pilon-Smits, 2005; Salt et al., 1998; Anderson et al., 1993).
The rate of exudation changes with the age of a plant, the availability of mineral
nutrients and the presence of contaminants (Chaudhry et al., 2005). The nature and the
quantity of root exudates, and the timing of exudation are crucial for a rhizoremediation
process. The root exudates mediate acquisition of minerals by plants and stimulate
microbial growth and activities in the rhizosphere in addition to changing some
physicochemical conditions. Plants might respond to chemical stress in the soil by
changing the composition of root exudates controlling, in turn, the metabolic activities
of rhizosphere microorganisms (Chaudhry et al., 2005). Some organic compounds in
root exudates may serve as carbon and nitrogen sources for the growth and long-term
survival of microorganisms that are capable of degrading organic pollutants (Pilon-
Smits, 2005; Salt et al., 1998; Anderson et al., 1993).
Cometabolism: Cometabolism is defined as the oxidation of non growth
substrates during the growth of an organism on another carbon or energy source
(Kuiper et al., 2004). Some co-metabolized recalcitrant pollutants such as the pesticide
lindane (organochlorine) are only transformed and not effectively mineralized by
microorganisms (Paul et al., 2005). Microbes living in the rhizosphere, Rhizomicrobia,
in turn, can promote plant health by stimulating root growth (regulators), enhancing
water and mineral uptake, and inhibiting growth of pathogenic or other, non-pathogenic
soil microbes (Pilon-Smits, 2005; Kuiper et al., 2004).
The microbial transformations of organic compounds are usually not driven by
energy needs but a necessity to reduce toxicity due to which microbes may have to
suffer an energy deficit (Chaudhry et al., 2005). Thus, the processes may be enhanced or
driven by the abundant energy that is provided by root exudates. Such stimulation of
soil microbial communities by root exudates also benefits plants through increased
availability of soil-bound nutrients and degradation of phytotoxic soil contaminants
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 199 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
(Chaudhry et al., 2005). This might allow the spread of roots into deeper soil layers.
Rhizomicrobia may also accelerate remediation processes by increasing the
humification of organic pollutants (Salt et al, 1998). In particular, the release of
oxidoreductase enzymes (e.g. peroxidase) by microbes, as well as by plant roots, can
catalyze the polymerization of contaminants onto the soil humic fraction and root
surfaces. Usually, several bacterial populations degrade pollutants more efficiently than
a single species/strain due to the presence of partners, which use the various
intermediates of the degradation pathway more efficiently (joint metabolism) (Kuiper
et al., 2004; Pelz et al., 1999). During rhizoremediation, the degradation of a pollutant, in
many cases, is the result of the action of a consortium of bacteria (Kuiper et al., 2004).
The colonization of different niches of plant roots by different strains has also been
recognized (Kuiper et al., 2001, 2004; Dekkers et al., 2000). Interestingly, the close
proximity of the different strains and the formation of mixed micro-colonies were
observed only in the presence of the pollutant. However, very few studies report the
directed introduction of a microbial strain or consortium for xenobiotic degradation
activities (bioaugmented rhizoremediation), which is able to efficiently colonize the
root (Korade and Fulekar, 2009, Kuiper et al., 2001; 2004).
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 200 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Roots
Root Pieces
Screw Cap Bottle
Serial Dilution
1 ml plate
Petri Dishes With Agar
Fungi, Bacteria and Actinomycetes
Sterile Petri Dish
Agar with Root
Colonies Growing Figure 1: Serial dilution of soil and plating methods for isolation of
microorganisms from soil, rhizosphere soil and root surface.
Factors affecting Bioremediation of pesticides in the soil environment:
Soil Conditions:
The success of bioremediation depends on a number of soil physico-chemical factors
such as moisture, redox conditions, temperature, pH, organic matter, nutrients and
nature, and amount of clay that affect microbial activity and chemical diffusion in soils.
Soil water affects not only the moisture available to microorganisms, but also the redox
conditions in soil that may lead to different biochemical reactions. Schroll et al. (2006)
quantified the effect of soil moisture on the aerobic microbial mineralization of selected
pesticides (isoproturon, benzolin-ethyl, and glyphosphate) in different soils. They found
a linear correlation (p < 0.0001) between increasing soil moisture (within a soil water
potential range of −20 and −0.015 MPa) and increased relative pesticide mineralization.
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 201 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Optimum pesticide mineralization was obtained at a soil water potential of −0.015 MPa.
Further increase in water reduced the pesticide mineralization because surplus water
restricts oxygen diffusion and availability and can make the environment anoxic.
Temperature:
Temperature and pH are the major factors affecting the biodegradation of
pesticides in soil. Temperature not only affects the rates of biochemical reactions, as all
microbial activities depend on thermodynamics, but also has a direct impact on cell
physiology-altering proteins and cell membrane permeability (Alberty, 2006; Guillot et
al., 2000; Mastronicolis et al., 1998). The bacterial isolates were able to rapidly degrade
fenamiphos and chlorpyrifos between 15 and 35◦C, but their degradation ability was
sharply reduced at 5 or 50◦C (Singh et al., 2006). Similar results were reported by
Siddique et al. (2002), who studied biodegradation of HCH isomers in soil slurry. They
observed that an incubation temperature of 30◦C was optimum for effective
degradation of α- and γ -HCH isomers.
pH:
The biodegradation of a compound is dependent on specific enzymes secreted by
microorganisms. These enzymes are largely pH-dependent and bacteria tend to have
optimum pH between 6.5 and 7.5, which equals their intracellular pH. A Pandoraea sp.
isolated from an enrichment culture (Okeke et al., 2002) degraded HCH isomers over a
pH range of 4 to 9 (Siddique et al., 2002), but the optimum pH for growth and
biodegradation of α- and γ -isomers of HCH in soil slurries was 9. Singh et al. (2006) also
reported the similar results while studying the biodegradation of organophosphate
pesticides in soil. Degradation rate was slower in lower pH soils in comparison with
neutral and alkaline soils. Though soil pH has a direct effect on biochemical reactions, it
may influence adsorption/desorption of pesticides on soil matrix and hence
bioavailability and biodegradation. Lower soil pH can increase the adsorption of weakly
acidic pesticides.
Boivin et al. (2005) compared the adsorption and desorption processes of five
pesticides (from very weak base to weakly acidic chemicals) in thirteen contrasting field
soils and found a significant correlation between bentazone (weakly acidic pesticide)
adsorption and soil pH. Sorption of the neutral form likely involves non-specific
interactions along with hydrophobic interactions and the presence of hydrogen bonds.
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 202 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
In the case of bentazone, the coexistence of both neutral and ionized forms could
explain the increased sorption at low pH values. No significant adsorption was observed
with the other weakly acidic pesticide (2, 4-D) used in the experiment due to its
complete ionization at lower pH and greater repulsion between electronegative charges
of soil constituents and those of the ionized molecules.
Soil organic matter:
Soil organic matter also affects biodegradation of pesticides in soil by providing
nutrients for cell growth and controlling pesticide movement by adsorption/desorption
processes. Perrin-Ganier et al. (2001) monitored biodegradation of isoproturon
(herbicide) by adding sewage sludge, nitrogen (N), and phosphorus (P) separately and
observed that N and P had the greatest effect on isoproturon degradation. Sewage
sludge did not affect isoproturon degradation significantly despite increase of organic
matter with sludge addition (Perrin-Ganier et al., 2001). In soil, the main source of
organic matter that provides nutrients is crop residues. Different groups of pesticides
behave differently in soils. Boivin et al. (2005) correlated adsorption of non-acidic
pesticides (atrazine, isoproturon, and trifluralin) to soil organic matter content. Singh et
al. (2006) studied the biodegradation of organophosphate pesticides (fenamifos and
chlorpyrifos) and did not find any impact of soil organic matter on the pesticide
biodegradation rates. In another study, Fenlon et al. (2007) found that diazinon
(organophosphate pesticide) only appreciably mineralized in two of the organic soils
when assessed in organically and conventially managed soils compared to cypermethrin
(pyrethroid), which degraded significantly in all the investigated soils.
Recent research studies implying rhizosphere bioremediation of pesticides:
Shaw and Burns, 2004 reported that the mineralization of [U-14C]2,4-
dichlorophenoxyacetic acid (2,4-D) in rhizosphere soil with no history of herbicide
application collected over a period of 0 to 116 days after sowing of Lolium perenne and
Trifolium pratense. The relationships between the mineralization kinetics, the number
of 2,4-D degraders, and the diversity of genes encoding 2,4-D/α-ketoglutarate
dioxygenase (tfdA) were investigated. The rhizosphere effect on [14C]2,4-D
mineralization (50 μg g−1) was shown to be plant species and plant age specific. In
comparison with nonplanted soil, there were significant (P < 0.05) reductions in the lag
phase and enhancements of the maximum mineralization rate for 25- and 60-day T.
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 203 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
pratense soil but not for 116-day T. pratense rhizosphere soil or for L. perenne
rhizosphere soil of any age. Numbers of 2,4-D degraders in planted and nonplanted soil
were low (most probable number, <100 g−1) and were not related to plant species or
age. Single-strand conformational polymorphism analysis showed that plant species
had no impact on the diversity of α-Proteobacteria tfdA-like genes, although an impact
of 2,4-D application was recorded. Results indicated that enhanced mineralization in T.
pratense rhizosphere soil is not due to enrichment of 2,4-D-degrading microorganisms
by rhizodeposits and an alternative mechanism in which one or more components of
the rhizodeposits induce the 2,4-D pathway was suggested.
Yu et al, 2003 reported the degradative characteristics of butachlor in non-
rhizosphere, wheat rhizosphere, and inoculated rhizosphere soils were measured. The
rate constants for the degradation of butachlor in non-rhizosphere, rhizosphere, and
inoculated rhizosphere soils were measured to be 0.0385, 0.0902, 0.1091 at 1 mg/kg,
0.0348, 0.0629, 0.2355 at 10 mg/kg, and 0.0299, 0.0386, 0.0642 at 100 mg/kg,
respectively. The corresponding half-lives for butachlor in the soils were calculated to
be 18.0, 7.7, 6.3 days at 1 mg/kg, 19.9, 11.0, 2.9 days at 10 mg/kg, and 23.2, 18.0, 10.8
days at 100 mg/kg, respectively. The experimental results show that the degradation of
butachlor can be enhanced greatly in wheat rhizosphere, and especially in the
rhizosphere inoculated with the bacterial community designated HD which is capable of
degrading butachlor. It was concluded that rhizosphere soil inoculated with
microorganisms-degrading target herbicides is a useful pathway to achieve rapid
degradation of the herbicides in soil.
Liao et al, 2008 reported the degradative characteristics of simazine (SIM),
microbial biomass carbon, plate counts of heterotrophic bacteria and most probably
number (MPN) of SIM degraders in uninoculated non-rhizosphere soil, uninoculated
rhizosphere soil, inoculated non- rhizosphere soil, and inoculated rhizosphere soil were
measured. At the initial concentration of 20 mg SIM/kg soil, the half-lives of SIM in the
four treated soils were measured to be 73.0, 52.9, 16.9, and 7.8 d, respectively, and
corresponding kinetic data fitted first- order kinetics. The experimental results
indicated that higher degradation rates of SIM were observed in rhizosphere soils,
especially in inoculated rhizosphere soil. The degradative characteristics of SIM were
found to be closely related to microbial process. Rhizosphere soil inoculated with
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 204 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
microorganisms-degrading target herbicides offering a useful pathway to achieve rapid
degradation of the herbicides in soil was suggested.
Pai et al, 2001 studied the fate of the fungicide mefenoxam in a containerized
rhizosphere system. The rhizosphere system used Zinnia angustifolia (Tropic Snow) in a
bark/sand potting mix and was compared to bulk potting mix (no plants). Rhizosphere
microbial populations were allowed to establish for 3 weeks prior to fungicide addition
(20 μg per g mix). Mefenoxam and degradation product concentrations were
determined by High HPLC or capillary electrophoresis after extraction. Seventy eight
percent of the fungicide originally applied to the rhizosphere was degraded after 21
days compared to 44% in bulk system (no plant). The primary degradation product was
the free acid N-(2, 6-dimethylphenyl)-N-(methoxyacetyl)-DL-alanine, which accounted
for 71% of the applied parent chemical after 30 days. N-(2,6-dimethylphenyl)-
acetamide was also detected, but in lesser amounts. Bacterial populations in the
rhizosphere was found to increase during the 30-day period, which was correlated with
an increase in degradation of the parent compound. Pure cultures of Pseudomonas
fluorescens and Chrysobacterium indologenes isolated from the rhizosphere system
degraded the applied fungicide (10 μg/ml) almost completely to the free acid within 54
h.
Sun et al, 2004 conducted an experiment to investigate the degradation of aldicarb,
an oxime carbamate insecticide, in sterile, non-sterile and plant-grown soils, and the
capability of different plant species to accumulate the pesticide. The degradation of
aldicarb in soil followed first-order kinetics. Half lives (t1/2) of aldicarb in sterile and
non-sterile soil were 12.0 and 2.7 days, respectively, which indicated that
microorganisms played an important part in the degradation of aldicarb in soil. Aldicarb
was found to disappear more quickly in the soil with the presence of plants, and t1/2 of
the pesticide were 1.6, 1.4 and 1.7 days in the soil grown with corn, mung bean and
cowpea, respectively. Comparison of plant-promoted degradation and plant uptake
showed that the enhanced removal of aldicarb in plant-grown soil was mainly due to
plant-promoted degradation in the rhizosphere.
Drakeford et al, 2003 studied the degradation of Isoxaben{N-[3-(1-ethyl-1-
methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide} is a pre-emergence herbicide
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 205 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
was studied in potting mix (80% bark, 20% sand) with three different regimes (sterile,
bulk and rhizosphere). The rhizosphere regime contained Switch Grass (Panicum
virgatum), and plants were allowed to grow for 14 days before adding isoxaben (10
μg/g potting mix). Isoxaben was degraded to 0.5 μg/g in 60 days giving a half-life of 7
days. Two degradation products were detected: 3-nitrophthalic acid in the rhizosphere
and bulk regimes and 4-methoxyphenol in the sterile regime. Microbial population
shifts were determined by fatty acid methyl ester profile analysis and were influenced
by the introduction of a plant (rhizosphere regime) and by isoxaben addition.
Korade and Fulekar, 2009 reported the potential of ryegrass for rhizosphere
bioremediation of chlorpyrifos in mycorrhizal soil by the green house pot culture
experiments. The pot cultured soil amended at initial chlorpyrifos concentration of 10
mg/kg was observed to be degraded completely within 7 days where the rest amended
concentrations (25–100 mg/kg) decreased rapidly under the influence of ryegrass
mycorrhizosphere as the incubation progressed till 28 days. This bioremediation of
chlorpyrifos in soil is attributed to the microorganisms associated with the roots in the
ryegrass rhizosphere, and the microorganisms surviving in the rhizospheric soil spiked
at highest concentration (100 mg/kg) was assessed and used for isolation of
chlorpyrifos degrading microorganisms. The potential degrader identified by 16s rDNA
analysis using BLAST technique was Pseudomonas nitroreducens PS-2. Further,
bioaugmentation for the enhanced chlorpyrifos biodegradation was performed using
PS-2 as an inoculum in the experimental set up similar to the earlier. The heterotrophic
bacteria and fungi were also enumerated from the inoculated and non-inoculated
rhizospheric soils. In bioaugmentation experiments, the percentage dissipation of
chlorpyrifos was 100% in the inoculated rhizospheric soil as compared to 76.24, 90.36
and 90.80% in the non-inoculated soil for initial concentrations of 25, 50 and 100
mg/kg at the 14th, 21st and 28th day intervals respectively.
Abhilash et al, 2011 reported the combined rhizoremediation potential of
Staphylococcus cohnii subspecies urealyticus in the presence of tolerant plant Withania
somnifera grown in lindane spiked soil. Withania was grown in garden soil spiked with
20 mg kg−1 of lindane and inoculated with 100 ml of microbial culture (8.1 × 106 CFU).
Effect of microbial inoculation on plant growth, lindane uptake, microbial biomass
carbon, dehydrogenase activity, residual lindane concentration and lindane dissipation
percentage were analyzed. The microbial inoculation significantly enhances the growth
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 206 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
and lindane uptake potential of test plant (p < 0.05). Furthermore, there was an
enhanced dissipation of lindane observed in microbial inoculated soil than the
dissipation rate in non-inoculated soil (p < 0.01) and the dissipation rate was positively
correlated with the soil dehydrogenase activity and microbial biomass carbon (p <
0.05). Study concluded that the integrated use of tolerant plant species and rhizospheric
microbial inoculation can enhance the dissipation of lindane, and have practical
application for the in situ remediation of contaminated soils.
Dubey and Fulekar (2011a and b) reported the experiment carried out to evaluate
the potential use of grass species Pennisetum pedicellatum for the rhizospheric
bioremediation of pesticides Chlorpyrifos. The effect of the three pesticides on the
germination of grass seeds was investigated using pesticide spiked soil at the
concentrations 10, 25, 50, 75 and 100 mg/kg, while unspiked soil has been taken as
control. The heterotrophic microbial numbers were also enumerated in the developing
rhizospheric zone and inthe bulk soil in order to assess developing microbial
associations for biodegeradation of pesticides in mycorrhizosphere. The research
finding shows that Chlorpyrifos was more toxic than Cypermethrin and Fenvalerate at
higher concentrations (75 and 100mg/kg) for the germination, survival and subsequent
growth of Cenchrus setigerus, and Pennisetum pedicellatum. The heterotrophic microbial
populations were found to be higher in the mycorrhizosphere soil of co-cropping
system of Cenchrus setigerus and Pennisetum pedicellatum as compared to individual
mycorrhizospheres of Cenchrus setigerus and Pennisetum pedicellatum, for all the three
pesticides at each concentration ranging from 10 mg/kg to 100mg/kg. This study will
help in selection plants for further investigation of the rhizospheric bioremediation of
Chlorpyrifos, Cypermethrin and Fenvalerate contaminated soil. Enhanced chlorpyrifos
degradation was reported in Pennisetum rhizosphere.
Conclusions:
The potential role of plants and associated rhizomicrobial population in facilitating
microbial degradation for in situ bioremediation of surface soils contaminated with
hazardous organic compounds is substantial. Support for this concept comes from the
fundamental microbial ecology of the rhizosphere, documented acceleration of
microbial degradation of agricultural chemicals in the root zone, and recent research
addressing degradation of agricultural and nonagricultural hazardous pesticides in the
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 207 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
rhizosphere. Further understanding of the critical factors influencing the plant-microbe-
toxicant interaction in soils will permit more rapid realization of this new approach to
in situ bioremediation.
References:
Abhilash P.C., Srivastava S., Srivastava P, Singh B., Jafri A., Singh S. (2011) Influence of rhizospheric microbial inoculation and tolerant plant species on the rhizoremediation of lindane Environmental and Experimental Botany, Elseveir Alberty, R.A. (2006) Biochemical reactions at specified temperature and various pHs. In Biochemical thermodynamics. Amos, P.W., and Younger, P.L. (2003) Substrate characterisation for a subsurface reactive barrier to treat colliery spoil leachate. Water Res., 37, 108–120. Anderson J.A., Kruger E.R., Coats J.R. (1994) Enhanced degradation of a mixture of three herbicides in the rhizosphere of a herbicide tolerant plant. Chemosphere 28: 1551–1557 Aprill W. & Sims R.C. (1990) Evaluation of the use of prairie grasses for stimulating polycyclic aromatic hydrocarbon treatment in soil. Chemosphere 20: 253-265. Barea J.M., Pozo M.J., Azcón R. & Azcón-Aguilar C. (2005) Microbial co-operation in the rhizosphere. J Exp Botany 56: 1761-1778. Bending, G.D., Lincoln, S.D., and Edmondson, R.N. (2006) Spatial variation in the degradation rate of the pesticides isoproturon, azoxystrobin and diflufenican Bioremediation and Phytorem-ediation of Pesticides in soil and its relationship with chemical and microbial properties. Environ. Pollut., 139, 279–287. Bhupathiraju, V.K., Krauter, P., Holman, H-Y.N., Conrad, M.E., Daley, P.F., Templeton, A.S., Hunt, J.R., Hernandez, M., and Alvarez-Cohen, L. (2002) Assessment of in-situ bioremediation at a refinery waste-contaminated site and an aviation gasoline contaminated site. Biodegradation, 13, 79–90. Boivin, A., Cherrier, R., and. Schiavon, M. (2005) A comparison of five pesticides adsorption and desorption processes in thirteen contrasting field soils. Chemosphere, 61, 668–676. Chang, S.W., Lee, S.J., and Je, C.H. (2005) Phytoremediation of atrazine by poplar trees: Toxicity, uptake, and transformation. J. Environ. Sci. Health, 40, 801–811. Charnay, M., Tuis, S., Coquet, Y., and Barriuso, E. (2005) Spatial variability in 14Cherbicide degradation in surface and subsurface soils. Pest Manage. Sci., 61,845–855.
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 208 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Chaudhry Q., Blom-Zandstra M., Gupta S. & Joner E.J. (2005) Utilising the synergy between plants and rhizosphere microorganisms to enhance breakdown of organic pollutants in the environment. Environ Sci Pollut Res 12: 34-48. Cunningham, S.D., Berti, W.R., and. Huang, J.W. (1995) Phytoremediation of contaminated soils. Trends Biotechnol., 13, 393–397. Dekkers L.C., Mulders I.H.M., Phoelich C.C., Chin-A-Woeng T.F.C., Wijfjes A.H.M. and Lugtenberg B.J.J. (2000)The sss colonization gene of the tomato-Fusarium oxysporum f. radicis-lycopersici biocontrol strain Pseudomonas fluorescens WCS365 can improve root colonization of other wild-type Pseudomonas spp. bacteria. Mol Plant Microbe Interact 13: 1177-1183. Dindal, D.L. (1990) Soil biology guide. New York: John Wiley & Sons, Inc. Ding, G., Novak, J.M., Amarasiriwardena, D., Hunt, P.G., and Xing, B. (2002) Soil organic matter characteristics as affected by tillage management. Soil Sci. Soc. Am. J., 66, 421–429. Drakeford Clyatt E. Dwight N.Camper, Melissa B. Riley Fate of isoxaben in containerized rhizosphere system Chemosphere, Volume 50, Issue 9, March 2003, Pages 1243-1247 Dubey, K.K., and Fulekar, M.H., (2011a) Effect of pesticides on the Seed Germination of Cenchrus setigerus and Pennisetum pedicellatum as Monocropping and Co-cropping System: Implications for Rhizospheric Bioremediation. Romanian Biotechnological Letters Vol. 16, No. 1, 5909-19 Dubey, K.K., and Fulekar, M.H., (2011b) Chlorpyrifos bioremediation in Pennisetum rhizosphere by a novel potential degrader Stenotrophomonas maltophilia MHF ENV20 World J Microbiol Biotechnol; DOI 10.1007/s11274-011-0982-1 Fenlon, K.A., Jones, K.C., and Semple, K.T. (2007) Development of microbial degradation of cypermethrin and diazinon in organically and conventionally managed soils. J. Environ. Monitor., 9, 510–515. Fulekar, M. H., (2005).Bioremediation technologies for environment. Indian Journal for Environmental Protection. 25, 358-364. Guillot, A., Obis, D., and Mistou, M.Y. (2000) Fatty acid membrane composition and activation of glycine-betaine transport in Lactococcus lactis subjected to osmotic stress. Int. J. Food Microbiol., 55, 47–51. Korade, D.L., Fulekar M.H., (2009), Rhizoremediation of Chlorpyrifos in mycorrhizospheric soil using rye grass. Journal of Hazardous Materials, 172, 2-3, (30)1344-1350 Kuiper I., Bloemberg G.V., & Lugtenberg B.J.J., (2001) Selection of a plant-bacterium pair as a novel tool for rhizostimulation of polycyclic aromatic hydrocarbon-degrading bacteria. Mol. Plant Microbe Interact 14: 1197-1205.
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 209 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Kuiper, I., Lagendijk, E.L., Bloemberg, G.V. & Lugtenberg, B.J.J., (2004) Rhizoremediation: A beneficial plant microbe interaction. Mol Plant Microbe Interact, 17: 6-15. Liao, M., Xie, X., (2008) Effects of combination of plant and microorganism on degradation of simazine in soil Journal of Environmental Sciences, 20 (2), pp. 195-198. Licht, L.A., and Isebrands, J.G., (2005) Linking phytoremediated pollutant removal to biomass economic opportunities. Biomass and Bioenergy, 28, 203–218. Lynch, J. M., and Whipps, J. M., (1990) Substrate flow in the rhizosphere. Plant Soil 129:1-10. Mastronicolis, S.K., German, J.B., Megoulas, N., Petrou, E., Foka, P., and Smith, G.M. (1998) Influence of cold shock on the fatty-acid composition of different lipid classes of the food-borne pathogen Listeria monocytogenes. Food Microbiol., 15,299–306 Melling, F.B., (1993) Soil microbial ecology: Applications in agricultural and environmental management. New York: Marcel Dekker. Morra, M.J., (1996) Bioremediation in soil: Influence of soil properties on organic contaminants and bacteria. In Crawford, R.L., and Crawford, D.L. (eds.) Bioremediation:Principles and application. Cambridge, UK: Cambridge University Press, pp. 35–60. Okeke, B.C., Siddique, T., Arbestain, M.C., and Frankenberger, W.T., (2002) Biodegradation of γ -hexachlorocyclohexane and α-hexachlorocyclohexane in water and soil slurry by Pandoraea sp. J. Agric. Food Chem., 50, 2548–2555. Pai, S.G., Riley, M.B., Camper, N.D., (2001) Microbial degradation of mefenoxam in rhizosphere of zinnia anguistifolia. Chemosphere, 577-582. Paul, D., Pandey, G., Pandey, J., & Jain, R.K., (2005) Accessing microbial diversity for bioremediation and environmental restoration. Trends Biotechol 23: 135-142. Pelz. O., Tesar, M., Wittich, R.M., Moore, E.R.B., Timmis, K.N. & Abraham, W.R., (1999) Towards elucidation of microbial community metabolic pathways; unraveling the network of carbon sharing in a pollutant degrading bacterial consortium by immunocapture and isotopic ratio mass spectrometry. Environ Microbiol, 167-174. Pilon-Smits E., (2005) Phytoremediation. Annu Rev Plant Biol 56: 15-39. Rasmussen, G. & Olsen, R.A., (2004) Sorption and biological removal of creosote-contaminants from groundwater in soil/sand vegetated with orchard grass (Dactylis glomerata) Adv Environ Res 8: 313-327. Salt, D.E., Smith, R.D., & Raskin, I., (1998) Phytoremediation. Annu Rev Plant Physiol 49: 643-668.
IJOART
International Journal of Advancements in Research & Technology, Volume 2, Issue 7, July-2013 210 ISSN 2278-7763
Copyright © 2013 SciResPub. IJOART
Sandman, E., Loos, M.A., (1984) Enumeration of 2, 4-D degrading microorganisms in soils and crop plant rhizospheres using indicator media: high populations associated with sugarcane (Saccharum officinarum), Chemosphere 13, 1073–1084. Sato, K. In Interrelationships between Microorganisms and Plants in Soil; Vancura, V., Kunc, F., Eds.; Elsevier: New York, 1989; pp. 335-42 Schroll, R., Becher, H.H., Dorfler, U., Gayler, S., Grundmann, S., Hartmann, H.P., and Ruoss, J. (2006) Quantifying the effect of soil moisture on the aerobic microbial mineralization of selected pesticides in different soils. Environ. Sci. Technol., 40, 3305–3312 Seibert, K., Fuehr, F., Cheng, H. H., (1981) In Theory and Practical Use of Soil-Applied Herbicides Symposium; European Weed Resource Society: Paris, pp. 137-46 Shaw, L.J., and Richard, G.B., (2004) Enhanced Mineralization of [U-14C] 2, 4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense Appl. Environ. Microbiol. 70(8): 4766–4774. Siddique, T., Okeke B.C., Arshad, M., and Frankenberger, W.T., Jr. (2002) Temperature and pH effects on biodegradation of hexachlorocyclohexane isomers in water and soil slurry. J. Agric. Food Chem., 50, 5070–5076. Singh, B.K., Walker, A., and Wright, D.J. (2006) Bioremedial potential of fenamiphos and chlorpyrifos degrading isolates: Influence of different environmental conditions. Soil Biol. Biochem., 38, 2682–2693. Stomp A.M., Han K.H., Wilbert S., Gordon M.P. & Cunningham S.D. (1994) Genetic strategies for enhancing phytoremediation. Ann NY Acad Sci 721: 481-492. Sun H., Xu J., Yang S., Liu G., Dai S., (2004) Plant uptake of aldicarb from contaminated soil and its enhanced degradation in the rhizosphere. Chemosphere; 54: 569–574 Vidali, M. (2001) Bioremediation: An overview. Pure and Applied Chemistry. 73, 1163–1172. Yu, Y.L., Chen, Y.X., Luo, Y.M., Pan X.D., He, Y.F., Wong, M.H., (2003 Rapid degradation of butachlor in wheat rhizosphere soil Chemosphere, 50 (6), 771-774.
IJOART