Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue11-12.oct2000:
Soil Biology & Biochemistry 32 (2000) 1475±1484
www.elsevier.com/locate/soilbio
Review
Ectomycorrhizas Ð extending the capabilities of rhizosphere
remediation?
Andrew A. Meharg a, John W.G. Cairney b,*
a
Department of Plant and Soil Science, University of Aberdeen, Cruickshank Building, St. Machar Drive, Aberdeen AB24 3UU, UK
b
Mycorrhiza Research Group, School of Science, University of Western Sydney, P.O. Box 10, Kingswood NSW 2747, Australia
Accepted 20 March 2000
Abstract
The potential of ectomycorrhizal (ECM) associations to facilitate clean-up of soil contaminated with persistent organic
pollutants (POPs) is considered. Most ECM fungi screened for degradation of POPs (e.g. polyhalogenated biphenyls,
polyaromatic hydrocarbons, chlorinated phenols, and pesticides) are able to transform these compounds. Mineralization of
toluene, tetrachloroethylene and 2,4-dichlorophenol in intact ECM-association rhizospheres has also been demonstrated. We
review and consider the likely mechanisms by which ECM fungi can transform pollutants, the extent to which these capabilities
may be utilized practically in bioremediation, along with the potential advantages and disadvantages of using ECM associations
in bioremediation. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Mycorrhizas; Persistent organic pollutants; Bioremediation; Phytoremediation
1. Introduction
Considerable attention has been focused on the potential use of plants to remediate soils contaminated
with metal and persistent organic pollutants (POPs)
(Anderson et al., 1993; Salt et al., 1998). Rhizosphere
remediation technologies oer potentially cheap, low
disturbance approaches to decontaminating polluted
land. There is, however, concern regarding the timescale required for successful plant-mediated remediation (Anderson et al., 1993). Furthermore, although
generally considered to be a clean technology, plantbased remediation is not without environmental implications, particularly movement of contaminants into
plants and so, potentially into wild-life food chains
(Anderson et al., 1993).
Phytoremediation is widely applied as a catch-all
term for the use of plants to remediate both metal-
* Corresponding author. Tel.: +61-2-9685-9903; fax: +61-2-96859915.
E-mail address: j.cairney@nepean.uws.edu.au (J.W.G. Cairney).
and POP-contaminated soils. The term is certainly suited to hyperaccumulation of metals by plants, since
the plant tissues are the repository of the pollutants
(Salt et al., 1998). Where plants are used to remediate
POPs, however, we prefer the term `rhizosphere remediation', because POP degrading activity will, in most
scenarios, occur in the rhizosphere, rather than in the
plant per se.
Enhanced degradation or mineralization in the rhizosphere has been demonstrated for a range of pesticides, polyaromatic hydrocarbons (PAHs), oil,
surfactants and chlorinated alkanes (Anderson et al.,
1993). While it is thought that enhanced rhizosphere
degradation is due to plant-stimulated microbial activity in the rhizosphere, other biological (e.g. bacterial
plasmid transfer) and physical (e.g. pollutants drawn
into the rhizosphere by the transpiration stream,
alteration of soil structure) factors may also play a
role. Rhizosphere microorganisms may not degrade
POPs to yield energy, rather they may co-metabolize
them as a consequence of utilizing plant-derived cyclic
compounds. For example, plant phenolics, such as
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 7 6 - 6
1476
Table 1
Persistent organic pollutant degrading capabilities (+ or ÿ)a for a range of ectomycorrhizal fungi
Compoundsb
Phe
Ant
Flu
Pyr
Per
PCBa
PCBb
PCBc
PCBd
PCBe
PCBf
PCBg
PCBh
PCBi
PCBj
PFB
TNT
DCP
Chl
Referencec
1
1
1
1
1
2d
2
2
2
2
2
2
2
2
2
3
4
5
6
+
ÿ
+
+
+
+
+
+
+
+
+
+
ÿ
ÿ
+
Species
ÿ
+
ÿ
+
ÿ
ÿ
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
ÿ
+
ÿ
ÿ
ÿ
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
ÿ
+
+
+
+
+
+
ÿ
ÿ
ÿ
+
+
+
+
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
±
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
+
ÿ
+
+
ÿ
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
+
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
ÿ
+
+
ÿ
+
ÿ
ÿ
+
ÿ
ÿ
+
ÿ
+
ÿ
+
+
+
+
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
+
+
+
+
+
+
+
+
+
+
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
+
+
+
+
+
ÿ
ÿ
ÿ
+
A.A. Meharg, J.W.G. Cairney / Soil Biology & Biochemistry 32 (2000) 1475±1484
Amanita muscaria
A. rubescens
A. spissa
Boletus grevellei
Bysporia terrestris
Cenococcum geophilum
Gautieria caudata
G. crispa
G. othii
Genabea cerebriformis
Hebeloma crustuliniforme
H. cylindrosporum
H. hiemale
H. sarcophyllum
H. sinapizans
Hysterangium gardneri
Laccaria amethystina
Lactarius deliciosus
L. deterrimus
L. rufus
L. torminosus
Morchella conica
M. elata
M. esculenta
Paxillus involutus
Piloderma croceum
Pisolithus tinctorius
Radiigera atrogleba
Rhizopogon luteolus
R. roseolus
R. vinicolor
R. vulgaris
Russula aeruginea
R. foetens
Suillus bellini
S. bovinus
S. granulatus
S. luteus
S. variegatus
Thelophora terrestris
The symbol `+' indicates that compounds were degraded to some extent. In some cases this was only a small % of the total available, but in others degradation was signi®cant. See text and
original references for more details.
b
Compound codes: Phe, phenanthrene; Ant, anthracene; Flu, ¯uronthene; Pyr, pyrene; Per, perylene; PCBa, PCB-2,3; PCBb, PCB-2,2 '; PCBc, PCB-2,4 '; PCBd, PCB-4,4 '; PCBe, PCB-2,4,4 ';
PCBf, PCB-2,5,2 '; PCBg, PCB-2,5,4 '; PCBh, PCB-2,4,2 ',4 '; PCBi, PCB-2,5,2 ',5 '; PCBj, PCB-2,4,6,2 ',4 '; PFB, 4-¯uorobiphenyl; TNT, trinitrotoluene; DCP, 2,4-dichlorophenol; Chl, chlorpropham.
c
References: 1 = Gramss et al. (1999); 2 = Donnelly and Fletcher (1995); 3 = Green et al. (1999); 4 = Meharg et al. (1997a); 5 = Meharg et al. (1997b); 6 = Rouillon et al. (1989).
d
Only PCBs that were degraded by at least one taxon are reported. A further 9 (4±6 chlorinated) PCBs were tested by Donnelly and Fletcher (1995), but were not degraded by any of the
fungi tested.
a
Tricholoma lascivum
T. terreum
Tylospora ®brillosa
+
+
+
+
+
+
+
+
+
+
+
+
A.A. Meharg, J.W.G. Cairney / Soil Biology & Biochemistry 32 (2000) 1475±1484
1477
catechin and coumarin serve as co-metabolites for
degradation of polychlorinated biphenyls (PCBs) by
bacteria (Salt et al., 1998). Enzymes used to degrade
plant-derived compounds by free-living rhizosphere microbial biomass may also degrade POPs. This is
suggested, for example, by the results of Sanderman
and Loos (1984), who isolated 2,4-D degrading bacteria
from the rhizospheres of sugarcane growing in soil
that had not previously been exposed to the chemical.
The full suite of enzymatic processes required to
degrade a POP may not be possessed by a single
organism. The rhizosphere comprises a complex consortium of microorganisms and POP degradation by
rhizosphere consortia has been demonstrated by Lappin et al. (1995) for the pesticide mecoprop.
There are a number of important challenges to be
considered in using plants to remediate POP-contaminated sites. Such sites are rarely contaminated with
only a single pollutant and the plant species used must
be resistant to all contaminants present. Often industrial sites oer very poor habitats for plant growth due
to poor nutritional status and soil structure. For rhizosphere remediation to be optimized, the surface area of
root±soil contact must be considered, as this is a crucial factor in the eectiveness and speed of remediation. For sites contaminated with multiple pollutants,
the enzymatic activities of the organisms deployed to
facilitate remediation need to be capable of degrading
a wide range of POPs. These criteria, along with
further potential remediation bene®ts, are met by ectomycorrhizal (ECM) associations (Donnelly and
Fletcher, 1994), and it is the rhizosphere remediation
potential of ECM associations that is considered in
this review.
2. Why consider ECM associations for use in
remediation?
A range of ECM fungi have been shown to degrade
®ve major classes of environmentally important POPs.
Out of the 42 species of ECM fungi screened so far, 33
have been shown to degrade one or more classes of
the chemicals (Table 1). Lower (2±3) chlorinated PCBs
were readily degraded by eight out of the 13 species
screened, while a limited number of the 4±5 chlorinated biphenyls were degraded by only two species
(Donnelly and Fletcher, 1995). Only one out of 21
species tested in a further study could not degrade at
least one PAH, with over half degrading all ®ve PAHs
to which they were exposed (Gramss et al., 1999).
Interestingly, where a species could not degrade the
full suite of PAHs with which it was challenged, there
was a preference to degrade 4±5 ring PAHs, rather
than the simpler three ring PAH structure. Some ECM
fungi have also been shown to degrade chlorpropham
1478
A.A. Meharg, J.W.G. Cairney / Soil Biology & Biochemistry 32 (2000) 1475±1484
(Rouillon et al., 1989), dichlorophenol (Meharg et al.,
1997a), trinitrotoluene (Meharg et al., 1997b) and
mono¯uorobiphenyl (Green et al., 1999). Although
rates of degradation of some POPs by certain ECM
fungi appear somewhat lower than those reported for
some wood-rotting fungi (e.g. Gramms et al., 1999),
we are mindful that the eciency of degradation will
depend on a number of factors including growth rates
of fungi, culture conditions, incubation time and nutrient. Some ECM fungi have, for example, been shown
to remove up to 90% of trinitrotoluene (Meharg et al.,
1997) and 95% of mono¯uorobiphenyl (Green et al.,
1999) from solution culture. Similarly, up to 50%
removal of PAHs, including for very recalcitrant compounds, such as benzo-(a)-pyrene from solution culture
has been observed for some ECM taxa (Braun-Lullemann et al., 1999; Gramms et al., 1999). Importantly,
all ECM fungal isolates tested to date have been
obtained from unpolluted soils, suggesting that ECM
fungi may express POP-degrading activities in their
natural habitats. It is therefore, likely that the enzymes
mediating POP degradation have a fundamental role
in the normal ecology of ECM.
The ability to degrade POPs, while growing in symbiosis with a host plant is clearly a central consideration in using ECM fungi in remediation of
contaminated soils. To date, there have been only two
investigations of degradation under aseptic conditions
with an intact fungus±plant system. Sarand et al.
(1999) found no evidence for m-toluene degradation by
Suillus bovinus either in axenic culture or while growing with a plant partner. Meharg et al. (1997a), however, demonstrated that isolates of Suillus variegatus
and Paxillus involutus could mineralize 2,4-dichlorophenol both in axenic culture and in symbiosis with
Pinus sylvestris. During growth in nutrient replete axenic culture P. involutus mineralized up to 17% of the
substrate over 17 days. Mineralization rates were
lower (
www.elsevier.com/locate/soilbio
Review
Ectomycorrhizas Ð extending the capabilities of rhizosphere
remediation?
Andrew A. Meharg a, John W.G. Cairney b,*
a
Department of Plant and Soil Science, University of Aberdeen, Cruickshank Building, St. Machar Drive, Aberdeen AB24 3UU, UK
b
Mycorrhiza Research Group, School of Science, University of Western Sydney, P.O. Box 10, Kingswood NSW 2747, Australia
Accepted 20 March 2000
Abstract
The potential of ectomycorrhizal (ECM) associations to facilitate clean-up of soil contaminated with persistent organic
pollutants (POPs) is considered. Most ECM fungi screened for degradation of POPs (e.g. polyhalogenated biphenyls,
polyaromatic hydrocarbons, chlorinated phenols, and pesticides) are able to transform these compounds. Mineralization of
toluene, tetrachloroethylene and 2,4-dichlorophenol in intact ECM-association rhizospheres has also been demonstrated. We
review and consider the likely mechanisms by which ECM fungi can transform pollutants, the extent to which these capabilities
may be utilized practically in bioremediation, along with the potential advantages and disadvantages of using ECM associations
in bioremediation. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Mycorrhizas; Persistent organic pollutants; Bioremediation; Phytoremediation
1. Introduction
Considerable attention has been focused on the potential use of plants to remediate soils contaminated
with metal and persistent organic pollutants (POPs)
(Anderson et al., 1993; Salt et al., 1998). Rhizosphere
remediation technologies oer potentially cheap, low
disturbance approaches to decontaminating polluted
land. There is, however, concern regarding the timescale required for successful plant-mediated remediation (Anderson et al., 1993). Furthermore, although
generally considered to be a clean technology, plantbased remediation is not without environmental implications, particularly movement of contaminants into
plants and so, potentially into wild-life food chains
(Anderson et al., 1993).
Phytoremediation is widely applied as a catch-all
term for the use of plants to remediate both metal-
* Corresponding author. Tel.: +61-2-9685-9903; fax: +61-2-96859915.
E-mail address: j.cairney@nepean.uws.edu.au (J.W.G. Cairney).
and POP-contaminated soils. The term is certainly suited to hyperaccumulation of metals by plants, since
the plant tissues are the repository of the pollutants
(Salt et al., 1998). Where plants are used to remediate
POPs, however, we prefer the term `rhizosphere remediation', because POP degrading activity will, in most
scenarios, occur in the rhizosphere, rather than in the
plant per se.
Enhanced degradation or mineralization in the rhizosphere has been demonstrated for a range of pesticides, polyaromatic hydrocarbons (PAHs), oil,
surfactants and chlorinated alkanes (Anderson et al.,
1993). While it is thought that enhanced rhizosphere
degradation is due to plant-stimulated microbial activity in the rhizosphere, other biological (e.g. bacterial
plasmid transfer) and physical (e.g. pollutants drawn
into the rhizosphere by the transpiration stream,
alteration of soil structure) factors may also play a
role. Rhizosphere microorganisms may not degrade
POPs to yield energy, rather they may co-metabolize
them as a consequence of utilizing plant-derived cyclic
compounds. For example, plant phenolics, such as
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 7 6 - 6
1476
Table 1
Persistent organic pollutant degrading capabilities (+ or ÿ)a for a range of ectomycorrhizal fungi
Compoundsb
Phe
Ant
Flu
Pyr
Per
PCBa
PCBb
PCBc
PCBd
PCBe
PCBf
PCBg
PCBh
PCBi
PCBj
PFB
TNT
DCP
Chl
Referencec
1
1
1
1
1
2d
2
2
2
2
2
2
2
2
2
3
4
5
6
+
ÿ
+
+
+
+
+
+
+
+
+
+
ÿ
ÿ
+
Species
ÿ
+
ÿ
+
ÿ
ÿ
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
ÿ
+
ÿ
ÿ
ÿ
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
ÿ
+
+
+
+
+
+
ÿ
ÿ
ÿ
+
+
+
+
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
±
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
+
ÿ
+
+
ÿ
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
+
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
ÿ
+
+
ÿ
+
ÿ
ÿ
+
ÿ
ÿ
+
ÿ
+
ÿ
+
+
+
+
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
+
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
+
+
+
+
+
+
+
+
+
+
+
+
ÿ
ÿ
+
+
ÿ
ÿ
ÿ
ÿ
+
+
+
+
+
ÿ
ÿ
ÿ
+
A.A. Meharg, J.W.G. Cairney / Soil Biology & Biochemistry 32 (2000) 1475±1484
Amanita muscaria
A. rubescens
A. spissa
Boletus grevellei
Bysporia terrestris
Cenococcum geophilum
Gautieria caudata
G. crispa
G. othii
Genabea cerebriformis
Hebeloma crustuliniforme
H. cylindrosporum
H. hiemale
H. sarcophyllum
H. sinapizans
Hysterangium gardneri
Laccaria amethystina
Lactarius deliciosus
L. deterrimus
L. rufus
L. torminosus
Morchella conica
M. elata
M. esculenta
Paxillus involutus
Piloderma croceum
Pisolithus tinctorius
Radiigera atrogleba
Rhizopogon luteolus
R. roseolus
R. vinicolor
R. vulgaris
Russula aeruginea
R. foetens
Suillus bellini
S. bovinus
S. granulatus
S. luteus
S. variegatus
Thelophora terrestris
The symbol `+' indicates that compounds were degraded to some extent. In some cases this was only a small % of the total available, but in others degradation was signi®cant. See text and
original references for more details.
b
Compound codes: Phe, phenanthrene; Ant, anthracene; Flu, ¯uronthene; Pyr, pyrene; Per, perylene; PCBa, PCB-2,3; PCBb, PCB-2,2 '; PCBc, PCB-2,4 '; PCBd, PCB-4,4 '; PCBe, PCB-2,4,4 ';
PCBf, PCB-2,5,2 '; PCBg, PCB-2,5,4 '; PCBh, PCB-2,4,2 ',4 '; PCBi, PCB-2,5,2 ',5 '; PCBj, PCB-2,4,6,2 ',4 '; PFB, 4-¯uorobiphenyl; TNT, trinitrotoluene; DCP, 2,4-dichlorophenol; Chl, chlorpropham.
c
References: 1 = Gramss et al. (1999); 2 = Donnelly and Fletcher (1995); 3 = Green et al. (1999); 4 = Meharg et al. (1997a); 5 = Meharg et al. (1997b); 6 = Rouillon et al. (1989).
d
Only PCBs that were degraded by at least one taxon are reported. A further 9 (4±6 chlorinated) PCBs were tested by Donnelly and Fletcher (1995), but were not degraded by any of the
fungi tested.
a
Tricholoma lascivum
T. terreum
Tylospora ®brillosa
+
+
+
+
+
+
+
+
+
+
+
+
A.A. Meharg, J.W.G. Cairney / Soil Biology & Biochemistry 32 (2000) 1475±1484
1477
catechin and coumarin serve as co-metabolites for
degradation of polychlorinated biphenyls (PCBs) by
bacteria (Salt et al., 1998). Enzymes used to degrade
plant-derived compounds by free-living rhizosphere microbial biomass may also degrade POPs. This is
suggested, for example, by the results of Sanderman
and Loos (1984), who isolated 2,4-D degrading bacteria
from the rhizospheres of sugarcane growing in soil
that had not previously been exposed to the chemical.
The full suite of enzymatic processes required to
degrade a POP may not be possessed by a single
organism. The rhizosphere comprises a complex consortium of microorganisms and POP degradation by
rhizosphere consortia has been demonstrated by Lappin et al. (1995) for the pesticide mecoprop.
There are a number of important challenges to be
considered in using plants to remediate POP-contaminated sites. Such sites are rarely contaminated with
only a single pollutant and the plant species used must
be resistant to all contaminants present. Often industrial sites oer very poor habitats for plant growth due
to poor nutritional status and soil structure. For rhizosphere remediation to be optimized, the surface area of
root±soil contact must be considered, as this is a crucial factor in the eectiveness and speed of remediation. For sites contaminated with multiple pollutants,
the enzymatic activities of the organisms deployed to
facilitate remediation need to be capable of degrading
a wide range of POPs. These criteria, along with
further potential remediation bene®ts, are met by ectomycorrhizal (ECM) associations (Donnelly and
Fletcher, 1994), and it is the rhizosphere remediation
potential of ECM associations that is considered in
this review.
2. Why consider ECM associations for use in
remediation?
A range of ECM fungi have been shown to degrade
®ve major classes of environmentally important POPs.
Out of the 42 species of ECM fungi screened so far, 33
have been shown to degrade one or more classes of
the chemicals (Table 1). Lower (2±3) chlorinated PCBs
were readily degraded by eight out of the 13 species
screened, while a limited number of the 4±5 chlorinated biphenyls were degraded by only two species
(Donnelly and Fletcher, 1995). Only one out of 21
species tested in a further study could not degrade at
least one PAH, with over half degrading all ®ve PAHs
to which they were exposed (Gramss et al., 1999).
Interestingly, where a species could not degrade the
full suite of PAHs with which it was challenged, there
was a preference to degrade 4±5 ring PAHs, rather
than the simpler three ring PAH structure. Some ECM
fungi have also been shown to degrade chlorpropham
1478
A.A. Meharg, J.W.G. Cairney / Soil Biology & Biochemistry 32 (2000) 1475±1484
(Rouillon et al., 1989), dichlorophenol (Meharg et al.,
1997a), trinitrotoluene (Meharg et al., 1997b) and
mono¯uorobiphenyl (Green et al., 1999). Although
rates of degradation of some POPs by certain ECM
fungi appear somewhat lower than those reported for
some wood-rotting fungi (e.g. Gramms et al., 1999),
we are mindful that the eciency of degradation will
depend on a number of factors including growth rates
of fungi, culture conditions, incubation time and nutrient. Some ECM fungi have, for example, been shown
to remove up to 90% of trinitrotoluene (Meharg et al.,
1997) and 95% of mono¯uorobiphenyl (Green et al.,
1999) from solution culture. Similarly, up to 50%
removal of PAHs, including for very recalcitrant compounds, such as benzo-(a)-pyrene from solution culture
has been observed for some ECM taxa (Braun-Lullemann et al., 1999; Gramms et al., 1999). Importantly,
all ECM fungal isolates tested to date have been
obtained from unpolluted soils, suggesting that ECM
fungi may express POP-degrading activities in their
natural habitats. It is therefore, likely that the enzymes
mediating POP degradation have a fundamental role
in the normal ecology of ECM.
The ability to degrade POPs, while growing in symbiosis with a host plant is clearly a central consideration in using ECM fungi in remediation of
contaminated soils. To date, there have been only two
investigations of degradation under aseptic conditions
with an intact fungus±plant system. Sarand et al.
(1999) found no evidence for m-toluene degradation by
Suillus bovinus either in axenic culture or while growing with a plant partner. Meharg et al. (1997a), however, demonstrated that isolates of Suillus variegatus
and Paxillus involutus could mineralize 2,4-dichlorophenol both in axenic culture and in symbiosis with
Pinus sylvestris. During growth in nutrient replete axenic culture P. involutus mineralized up to 17% of the
substrate over 17 days. Mineralization rates were
lower (