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Biotechnology and Food Science
Review article
Biotechnol Food Sci 2019, 83 (1), 13-30 http://www.bfs.p.lodz.pl
Mushrooms of the Pleurotus genus – properties
and application
Małgorzata Grabarczyk1*, Wanda Mączka1, Katarzyna Wińska1,
Cecylia Miłowana Uklańska-Pusz2
1 Department of Chemistry, Wrocław University of Environmental and Life
Sciences, Norwida 25, 50-375 Wrocław, Poland
2 Department Of Horticulture, Wrocław University of Environmental and Life
Sciences, pl. Grunwaldzki 24, 50-363 Wroclaw, Poland
*malgorzata.grabarczyk@upwr.edu.pl
Received: 15 November 2018/Available on-line: 15 March 2019
Abstract: Mushrooms of the Pleurotus genus are found naturally in forests
in almost all latitudes where they are responsible for the decomposition
of wood. These fungi are valuable to cultivate and eat, as they are source
of valuable nutrients and healing ingredients. Mycelium of white rot is
known for its bioremediation abilities, including the accumulation of heavy
metals and chlorinated aromatic hydrocarbons. Mushrooms of the
Pleurotus genus have also been found applicable in the biotransformation
of unsaturated terpenoid compounds. These reactions involve hydroxylation at
the allyl position and subsequent oxidation of the introduced hydroxyl
group. The article presents a number of applications of various strains of
fungi of the Pleurotus genus.
Keywords: Pleurotus, biotransformation, bioremediation, biodegradation.
Introduction
Mushrooms of the Pleurotus genus, known as oyster mushrooms, are the main
basic decomponenters of wood and plant residues. They grow mainly on decayed
wood, but they are also capable of parasiting on living trees, infecting them with
white rot [1]. Mycelium of white rot, i.e. oyster mushrooms, has bioremediation
properties, cleansing contaminated soil with oil derivatives or polycyclic
aromatic hydrocarbons or heavy metals [2].
Oyster mushrooms are found naturally in almost all latitudes except Antarctica,
also in tropical and subtropical forests. Due to different growth conditions,
mycologists have distinguished many species and types [3]. Mushrooms of this
type are valuable to cultivate and eat. Their fruiting bodies are sources of easily
absorbed proteins, carbohydrates, amino acids, B vitamins (thiamine, riboflavin
and niacin), vitamin D and mineral salts (calcium, phosphorus, iron),
characterized by low fat concentration [4-6]. In addition, they are sources of
pro-health substances, including antibacterial, antifungal, immunomodulatory,
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14
anti-inflammatory properties as well as reducing blood sugar and cholesterol
levels [7].
Mushrooms of the Pleurotus genus fulfill a dual role in the environment. They
are capable of colonizing and degrading a large number of lignocellulosic
residues, and as edible and cultivated mushrooms they are a source of valuable
nutrients and healing properties. These fungi require a shorter growth time
compared to other edible fungi and are relatively rarely attacked by diseases and
pests and can be cultivated [5,8].
Cultivation of oyster mushrooms
Mushroom Pleurotus ostreatus (Fr.) Kumm., used in cultivation for over 100
years, is now in the third place in the world in terms of production volume, after
champignon mushrooms and Lentinula edodes (shiitake) [9]. The size and quality
of yield depends on the growth conditions, i.e. the temperature and humidity of
the substrate and air and acidity of the medium, as well as on the variety or
species and the type of culture medium [10]. Oyster mushroom, as a saprophytic
mushroom uses cellulose, hemicellulose and lignin for its growth, therefore is
can be grown on wood, sawdust, straw of various species, maize settlements and
other agricultural wastes. However, because it grows and yields faster on straw
than on wood, its cultivation in Europe is most often carried out on straw,
subjected to pasteurization [3, 11-13].
In China, where mushroom production is responsible for over 70% of the
global market [9], the cultivation of Pleurotus spp. is mainly carried out on
sawdust with various additions. Wastes from the production of cotton and cereal
straw, especially rice are also used, but on a smaller scale [12, 14]. The
availability of sawdust begins to be limited by the development of the Chinese
poultry industry, therefore it is suggested to use wheat and rice straw, which is
agricultural waste, currently unused. Additional enrichment of the straw of these
species with the addition of cotton seed bags significantly improves the quality
and yield of oyster mushroom compared to the surface of the straw itself [14].
Because China is also a potentate in the cultivation of herbs, research on the
use of waste from their production for the cultivation of oyster mushroom are
also conducted. The Jin team [15] used for this purpose, among others: sofora
root (Radix Sophorae flavescentis), sarsaparilla rhizome (Rhizoma Smilacis
glabrae) and other wastes coming from the pharmaceutical plant, added to the
culture medium from corn sludges. They significantly increased the protein
content and individual amino acids in fruiting bodies. They also increased the
antioxidant activity of P. ostreatus fruiting bodies.
In Africa, oyster mushrooms are grown mainly on sawdust, with the addition
of rice straw. Looking for nutritional supplements, Narh Mensah and his team
[16] used the addition of powdered pineapple skins. The addition of 2 and 5%
positively influenced the yield and nutritional value of the cultivars EM-1
cultivated this way. Solutions regarding the use of waste additives other than
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15
those used so far contribute both to increased efficiency and productivity as well
as to environmental protection, reducing the amount of waste deposited.
Mushroom cultivation is usually carried out under fully controlled conditions.
For oyster mushroom during mycelial growth in the culture medium, the
temperature should be 24ºC, relative humidity 85-95%, CO2 content from 5000
to 20000 ppm. During molding the initial temperature of the air should be
10-15ºC, relative humidity 95-100%, CO2 content below 1000 ppm, with light
access in the range of 1000-2000 lux. When growing sporocarps, the air
temperature should be in the range of 10-21ºC (depending on the species), and air
humidity in the range of 85-90% [13]. Depending on the technological
advancement of facilities used in mushroom cultivation, these conditions are met
to a lesser or greater extent. However, greater precision of the crop increases its
productivity as well as healthiness [8].
Both the culture medium and growth conditions play a huge role in the
cultivation and yielding of oyster mushroom. They are also dependent on the
degree of hygiene in the production process because the cultivation of oyster
mushrooms, like in champignon mushrooms, is an intense monoculture. Failure
to comply with hygienic standards results in increased occurrence of fungal and
bacterial diseases and pests [3, 8, 13]. Although, compared to other cultivated
mushroom species, oyster mushrooms are less frequently attacked by diseases
and pests [8], however, the use of protection measures is an important element in
their production.
The source of medicinal and nutritional substances
The fruiting bodies of fungi of the Pleurotus genus are a rich source of micro
and macro elements, such as copper, iron, zinc and sodium, potassium,
magnesium and phosphorus. Their amount depends to a large extent on the
species, age and size of the fungus, as well as the growing conditions. The
mushroom pilei contain primarily potassium and phosphorus, whose content
varies between 10-20 mg/100 g. The content of other minerals is smaller, on the
order of a few percent. Mushrooms of the Pleurotus genus are also characterized by
a high content of valuable nutrients. These are protein (20-25%), carbohydrates
(40-46%), amino acids (20-40%) and fiber (10-20%). Significantly, the fat content
is very low, it is within 10-20% of the dry matter [17].
In Chile there are two species of oyster mushroom: P. ostreatus and Pleurotus
sutherlandii, growing on the endemic Nothofagus tree. In one of them – P.
sutherlandii – lovastatin 1 (Figure 1) has been identified, a compound that
reduces cholesterol in the blood [4]. Successive researchers tested P. ostreatus
using two variants of fungal growth. In the first case fruiting bodies were
collected directly from the trees. In the second case, fruiting bodies of fungi that
were grown on wheat straw were harvested under greenhouse conditions. After
extracting with methanol and ethyl acetate, the content of lovastatin 1 in the
tested fungi was determined. It turned out that the content of this compound is
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0.4 to 2.07% on a dry weight in the case of cultivated fungi and 0.7 to 2.8% in
the case of naturally growing fungi. This means that much better source of
lovastatin 1 is oyster mushroom growing in the natural environment [18].
Figure 1. Formula of lovastatin
Two strains P. ostreatus DSM 1833 and Pleurotus sajor-caju CCB 019 were
tested as a part of the research on increasing the nutritional value of Pleurotus
fungi. Rice and banana straw were used as a plant material for growth. As a
result of the research, it was found that the type of culture medium did not affect
the carbohydrate content in both strains. P. ostreatus fruiting bodies were
characterized by lower humidity using rice straw than banana straw, whereas in
case of P. sajor-caju fruiting bodies it was the opposite. The total fat content was
higher in P. ostreatus than in P. sajor-caju when rice straw was used. Both
strains had a higher total fiber content when grown in rice straw. In turn, the
protein content was higher with the use of banana straw [5].
Biotransformation
Mushrooms of the Pleurotus genus have found usage in biotransformation of
terpenes. Lyophilized strain of Pleurotus sapidus suspended in Tris-HCl buffer
transformed (+)-valencene 2 into (+)-nootkaton 5. Additional products of this
reaction were two allyl alcohols -nootkatol 3 and -nootkatol 4. Further
experiments showed that only -nootkatol 4 was an intermediate product in the
oxidation of valencene 2 to nootkaton 5. As a result of genetic tests, it was
confirmed that the oxygenase protein present in P. sapidus is similar to the
lipoxygenases found in Aspergillus ochraceus, Aspergillus fumigatus, Gibberella
moniliformis and Laccaria bicolor [19]. Lipoxygenases belong to the group of
dioxygenases containing in their structure an iron ion, without the presence of
a heme structure. Such enzymes are found in plants, animals, bacteria and fungi.
Lipoxygenases are responsible for the oxidation reactions of double bonds
of polyunsaturated fatty acids. In this case, an alternative two-step mechanism
of enzyme action was proposed, consisting of introducing the hydroxyl group in
the allyl position and then oxidizing this group to the ketone.
O
OO
OH O
1
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17
Figure 2. Biotransformation of valencene
Studies on biotransformation of valencene were continued by subsequent
researchers. They found that the intermediate products of hydroxylation of
compound 2 are hydroperoxides, the formation of which depends on the presence
of valencene dioxygenase in P. sapidus. The mechanism proposed by the authors
is similar to the catalytic mechanism of action of known lipoxygenases.
Dioxygenases, such as lipoxygenases, initiate a reaction from detachment of the
hydrogen atom from the substrate molecule. The resulting hydroperoxides are
stabilized by introducing the hydroperoxide group in the allylic position. The
reaction mechanism assumes the formation of two intermediate forms A and B
(Figure 2) [20].
Figure 3. Biotransformation of valencene
The P. sapidus strain was also used to carry out biotransformation of kar-3-
ene 6. The transformations were carried out in the aqueous culture of the strain
for 4 hours. After this time, compounds 7, 8 and 9 were obtained as the main
products (Figure 4). It was found that the mechanism of formation of these
compounds is consistent with the action mechanism of dioxygenases presented
OH OH
O
+
234
5
OOH HOO
OH
+
2
5
AB
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earlier. The formation of appropriate ketones is preceded by the formation of
transitional hydroperoxide forms and allyl alcohols [21].
Figure 4. Biotransformation of car-3-ene
The next substrates used for biotransformation performed with the P. sapidus
strain were allyl spiroethers 10, 11, 14 and 15. The lyophilisate P. sapidus suspended
in Tris buffer was used for the reaction. Biotransformation were carried out at
room temperature for 48 hours. It was found that the structure of the substrate
significantly influences the course of the reaction. Compounds 10 and 11 were
transformed into the corresponding lactones 12 and 13, while their structural
analogies 14 and 15 did not undergo any transformations. The conversion rate for
compounds 10 and 11 was 77% and 99%, respectively (Figure 5).
Figure 5. Biotransformation of spiroethers
Under similar conditions biotransformation of vitispirane 16 naturally
occurring in grape juice was carried out. As a result, ketoalcohol 17 and two
diastereoisomeric diols 19 and 20 were obtained. The 80% of the substrate was
converted. The mechanism proposed by the authors assumes that the intermediate
product of this reaction could be epoxide 18, converted by hydrolysis to diols 19
and 20. In turn these compounds could be oxidized to product 17 (Figure 6) [22].
O
O
O
++
67 8 9
OO
O
O
OO
OO
10 12
11
14
15
13
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19
Figure 6. Biotransformation of vitispirane
Pleurotus euosmus DSM 5331, P. ostreatus DSM 5339, P. sajor-caju DSM
1020 and P. sapidus DSM 8266 strains were used to carry out biotransformation
of R-(+)-limonene 21. It was found that only P. sapidus was able to hydroxylate
this compound to an equimolar cis/trans mixture of carveols 22 after 7 days of
the process. The same strain (P. sapidus) was then used to oxidize enantiomeric
carveols to carvone 23. Studies have shown that trans-(-)-carveol was converted
to enantiomerically pure R-(-)-carvone during 4 days with 94% efficiency. Under
the same conditions, cis-(+)-carveol was oxidized to S-(+)-carvone only in 55%
(Figure 7) [23].
Figure 7. Biotransformation of R-(+)-limonene
Heptachlor 24 is a representative of synthetic insecticides, used in the 60's and
70's of the last century. This compound was used to exterminate termites and
insects living in the soil. Heptachlor may oxidize to epoxide, which is more
durable and more toxic than the parent compound. Both compounds are found in
soil all over the world. Heptachlor has toxic effects on the human body by
attacking the central nervous system. Because fungi of the Pleurotus genus are
able to biodegrade polychlorinated compounds, this time it was decided to use
them for biotransformation. Heptachlor 24 and its epoxide 25 were used as
substrates, whereas P. ostreatus BM9073 as a bioreagent. This microorganism
OOOH
O
OOH
OH
OOH
OH
O
O
16 17
19
+
20
+
18
oxidation
hydrolysis
oxidation
OH O
21 22 23
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was grown on several culture media. The medium composed of 1% glucose,
1.2 mM ammonium tartrate and 20 mM sodium acetate (HN) and medium
containing potato dextrose broth (PDB) proved to be the best. In both cases,
complete conversion of heptachlor was observed after 14 days of incubation. The
biotransformation products were heptachlor epoxide 25 (about 65%), chlordene
26 (about 23%) and 1-hydroxy chlordene 27 (about 2%). The heptachlor epoxide
25 was in turn transformed into diol 28 at 8% and 31% respectively.
The resulting final products as hydroxy derivatives may show less toxicity than
the starting compounds (Figure 8) [24].
Figure 8. Heptachlor and its derivatives
Bioaccumulation of heavy metals
The characteristic feature of white rot fungi, to which P. ostreatus belongs, is
the ability to accumulate heavy metals. P. ostreatus has been tested for its
potential to completely remove copper, nickel, zinc and chromium from the
water. A solution consisting of 23.56 mg of Cu (II), 54.83 mg of Ni (II), 42.87
mg of Zn (II) and 93.54 mg of Cr (VI) dissolved in 1 dm3 of water was used in
the experiment. Various parameters were examined, such as the effect of pH, the
amount of biomass, equilibrium time, mixing intensity, temperature and initial
concentrations of metal ions. It was found that the maximum adsorption of Ni
(II), Cu (II) and Zn (II) ions occurred in the pH range 4.5-5.0, while for Cr (VI)
ion the best results were obtained at a pH of 2.5. Studies on the effect of biomass
amount showed that during increasing the biomass from 0.1 to 0.3 g, an increase
in efficiency in removing metal ions was observed. Further increasing the amount
of biomass from 0.4 to 0.8 g had no significant effect on biosorption.
Observations conducted during the process over time proved that in the first
15 minutes there was a rapid increase in the sorption of metal ions due to their
rapid uptake by fungi. Then the rate of metal removal increased gradually and
Cl Cl
Cl Cl
Cl
Cl
Cl
Cl Cl
Cl Cl
Cl
Cl
Cl
O
Cl Cl
Cl Cl
Cl
Cl
Cl Cl
Cl Cl
Cl
Cl
OH
Cl Cl
Cl Cl
Cl
Cl
Cl
OH OH
24 25
26 27 28
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reached its maximum value within 120-150 min. Biosorption took place in two
phases. The first phase consisted in the rapid storage of metal ions on the surface
of the fungus, while the second involved the slow transfer of metal ions to the
cytoplasm of the cell by membrane transport or slow intracellular diffusion.
Temperature in the range of 20-45°C had no significant effect on biosorption.
The maximum fungal biosorption capacity was 8.06, 20.4, 3.22 and 10.75 mg/g
for Cu (II), Ni (II), Zn (II) and Cr (VI), respectively [25].
During the next tests, the ability of the immobilized P. ostreatus to remove Cd
(II) ions from contaminated water was tested. The biosorption capacity and
biosorption rate were determined depending on pH, temperature and cadmium
ions concentration. The tests showed that both the capacity and rate of
biosorption reached the value of 70.3% at pH 6. The increase of temperature
from 5ºC to 30ºC resulted in increased capacity and biosorption rate from 7.3%
to 72.6%. A different situation was observed when studying the effect of the
initial concentration of cadmium ions. The experiment was carried out by
increasing the initial concentration of cadmium from 25 to 200 mg/L. It has been
found that the biosorption capacity increases rapidly up to a concentration of 150
mg/L, and then remains constant. In turn, the biosorption rate decreases from
97% (25 mg/L) to 40% (200 mg/L). The best parameters allowing removal of
87% of cadmium from the water tested were: initial concentration of Cd (II) ions
of 200 mg/L, pH = 6 and temperature of 25°C [26].
In another experiment, soil originating from a municipal waste landfill was
used. The studied soil, fungi Pleurotus ostreatus along with straw used as
a source of nutrients were laid out with qualities. The whole was incubated for
22 days. It was found that after this time 68% of lead and 81.25% of nickel were
removed from the soil [27].
Cobalt is a micronutrient important for soil microorganisms and crop plants.
However, when the level of cobalt exceeds the acceptable limit, it can lead to soil
and crop contamination. One of the methods of removing excess cobalt from the
soil is to use the so-called spent mushroom substrate. The tested Chinese soil
samples (Brassica chinensis L.) were grown on the tested soil samples containing
the spent fungal substrate and cobalt. Within 28 days, the phyto-availability of
cobalt in the soil and its accumulation in cabbage were determined. It was found
that the best results were obtained when the concentration of spent fungal
substrate ranged from 8.86 to 9.51 g kg-1, the phyto-availability of cobalt in the
soil reached a minimum, while the biomass of cabbage reached a maximum. This
means that the used fungal substrate from Pleurotus ostreatus effectively reduces
the cobalt availability – limiting the possibility of transferring this metal to the
human body through the consumption of food [28].
Another method was the use of P. ostreatus immobilized on bentonite to
remove traces of heavy metals from the water. In the experiment, 200 mg of dry
mycelia mixed with 2 g of bentonite was used. The finished mixture was placed
in a chromatographic column. The solutions of test metals containing 2.5-25 μg
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of Cd (II) and Pb (II) in 100 ml of tap water of the selected pH were passed
through the column and the degree of their biosorption was determined. The
optimum pH value for both metals was pH = 5. The degree of sorption of metal
ions ranged from 85% to 90%. It has also been found that the optimal solution
flow rate through the column was 2.5 mL/min and the required contact time of
the solution with the substrate was 30 minutes. Once filled, the column can be
used 20 times without significant changes in the recovery of metal ions. The
described method may be a cheaper alternative to activated carbon used to purify
water from trace amounts of heavy metals [29].
Biodegradation
Carbamazepine (CBZ) 29 is an anticonvulsant used mainly for the treatment
of epilepsy. This compound is slightly removed in municipal wastewater
treatment plants and as a result it accumulates in the natural environment.
Unfortunately, it has toxicological effects on aquatic organisms. The use for
biodegradation of Cunninghamella elegant, Umbelopsis ramanniana, Trametes
versicolor or Ganoderma lucidum proved that these fungi are able to metabolize
carbamazepine in 25-60% during 17 days of incubation. In the next experiment
strains of the Pleurotus genus: Florida N001, PC9 and Florida F6 were tested.
It was observed that these strains degraded CBZ in the range from 48 to 99%.
The best result was observed for the PC9 strain, so it was used for further
research to determine the mechanism of CBZ biodegradation. Previous studies
have suggested that two enzymatic mechanisms may participate in the oxidation
of CBZ: the ligninolytic system of white rot fungi and the CYP450
monooxygenase system [30, 31]. P. ostreatus PC9 was grown in various media
to check the accuracy of any of the above hypotheses. When both CYP450
(cytochrome P450) and MnP (manganese peroxidase) were active, 99% of
the added CBZ was eliminated from the solution and converted to 10,
11-epoxycarbamazepine 30. Inactivation of CYP450 or MnP also resulted in the
removal of CBZ, but at slower pace. In the case of absence of both systems, only
30% CBZ was removed during the 32 days of incubation. This means that both
systems participate in the oxidation of CBZ. The biotransformation product
epoxide 30 exhibits pharmacological activity similar to the activity of the parent
compound. However, after the activation of the CYP450 and MnP enzyme
systems, it was observed that the epoxide formed in the first step is gradually
converted to 10, 11 trans-diol 31. Such a compound may be bioavailable to other
microorganisms (Figure 9) [32].
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Figure 9. Biodegradation of carbamazepine
Aflatoxins are highly carcinogenic secondary metabolites that can contaminate
about 25% of crops, particularly in Africa and Asia. White rot fungi are able to
decompose aflatoxins in situ and ex situ. Therefore, studies were carried out to
determine the ability of P. ostreatus to degrade aflatoxin B1 (AFB1) 32 (Figure 10)
in naturally contaminated maize using standard cultivation techniques. It was
found that the growth of fungi was not inhibited by AFB1 contaminating maize
in an amount from 25 ng/g to 2500 ng/g. In addition, no detectable amount of
aflatoxin was observed in 100 × concentrated extracts of P. ostreatus fungi
grown on AFB1 contaminated corn, regardless of the P. ostreatus strain used or
the initial level of AFB1. This means that microorganisms, in particular white rot
fungi, can be used to degrade aflatoxin in crops intended for the consumption of
livestock [33].
Figure 10. Formula of aflatoxin B1
Bisphenol A (BPA) 33 is used for the production of plastics, mainly
polyesters, including polycarbonates, epoxy resins, polyethers, polysulphones.
This compound causes pollution of the natural environment, accumulating both
in water and in soil. In its removal from the environment, P. ostreatus may be
useful. The P. ostreatus O-48 strain was tested in vivo and in vitro. For the in
vivo experiment, a homogenized mycelium suspended in 20 ml of medium
containing glucose, peptone yeast extract and mineral salts to which 0.4 mM
BPA was added was used. After 12 days of transformation in stationary culture,
about 20% of BPA remained from the initial amount of compound. During the in
vitro experiment, the enzyme MnP (manganese peroxidase) produced by P.
ostreatus was used for the study. This enzyme was obtained from the liquid P.
ostreatus O-48 culture. The results of the experiments proved that BPA 33 was
O
O
OO
O
OMe
32
N
ONH2
N
ONH2
O
N
ONH2
OH OH
29 30 31
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metabolized to phenol 34, 4-isopropenylphenol phenol 35, 4-isopropylphenol 36
and hexestrol 37 (Figure 11) [34].
Figure 11. Biodegradation of bisphenol A
Fluoranthene 38 (Figure 12) is a representative of polycyclic aromatic
hydrocarbons, compounds that pose a threat to the natural environment. Many of
them are potentially genotoxic and carcinogenic. The main source of such
compounds is the burning of fossil fuels and industrial processing, but also forest
fires. It is known that white rot fungus is able to catalyze degradation of
polycyclic aromatic hydrocarbons to quinones and hydroxylated aromatic
compounds. Therefore, the P. ostreatus HP-1 strain was tested in a forest near
Gujarat, India. It was found that this fungus is able to grow on a medium
containing 50 mg/L of fluoranthene. The tests showed that after 54 days of
transformation, 54.09% of fluoranthene was degraded. It was also found that this
compound was broken down into an aliphatic compound [35].
Figure 12. Formula of fluoranthene
Atrazine (2-chloro-4-ethylamino-6-isopropylamine-s-triazine) 39 is an
herbicide frequently used to control weeds in sugar cane crops. Methods of
degradation of atrazine through the P. ostreatus strain INCQS 40310 was used
for the degradation of atrazine. Various types of culture media were used for
growing this fungus. In the first approach, a standard PDA medium consisting of
2 g glucose, 1 g peptone and 2 g yeast extract in 1 dm3 of water was used. In this
case, the degree of degradation of atrazine was 39.0% after 15 days. Then, the
OH OH
OH
OH OH
OH
OH
33
34
35 36 37
38
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effects of changes in the amount of nutrient components and the use of various
inorganic salts were tested. Preliminary studies have shown that the best effect
was achieved by increasing the glucose concentration to 8 g/L and adding ZnSO4
(0.002 g/L), FeSO4 (0.001 g/L) and MgSO4 (1 g/L) to the medium. The degree of
degradation of atrazine after 15 days of biodegradation increased to 71%.
Slightly worse result (63.3%) was obtained for medium with increased amount of
peptone (5 g/L) with addition of FeSO4 (0.001 g/L), MgSO4 (1 g/L) and CuSO4
(0.5 g/L). In the following experiment, the best medium was subjected to further
tests, namely the effect of only two inorganic salts of FeSO4 and MnSO4 at
different concentrations. It turned out that the best result was obtained when
0.001 g/L FeSO4 and 0.05 g/L MnSO4 were used. Under these conditions, after
94 days 94.5% atrazine was degraded. In addition, it has been found that as side
products of the degradation of atrazine 39, hydroxylated and chlorinated
compounds were formed: 2-chloro-4-amino-6-isopropylamine-s-triazine 40,
2-chloro-4-ethylamino-6-amino-s-triazine 41, 2-chloro-4,6-amino-s-triazine 42,
2-hydroxy-4-amino-6-isopropylamino-s-triazine 43, 2-hydroxy-4-ethylamino-
6-amino-s-triazine 44 (Figure 13) [36].
Figure 13. Atrazine and products of its degradation
DDT (1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane) 45 was the first of
synthetic pesticides that was used on a large scale as a plant protection product
from the 1940’s to the 1970’s of the last century. This compound has a long
half-life of 2-15 years in soil. Its decomposition products are mainly DDE
(1,1-dichloro 2,2-bis-(4-chlorophenyl)-ethane) 46 and DDD (1,1-dichloro-2,2-bis-
(4-chlorophenyl)-ethylene) 47 with properties similar to DDT, but with even
longer disintegration time. This compound is very harmful to higher organisms,
because it damages the nervous system, destroys DNA in the blood cells and
interferes with the synthesis and metabolism of endogenous hormones.
On a medium consisting of japanese cedar, sawdust, rice bran and water,
mycelium of P. ostreatus was inoculated, and the whole was incubated at 20°C
N
N
N
N
H
Cl
N
H
N
N
N
N
H
Cl
NH2
N
N
N
NH2
Cl
N
H
N
N
N
NH2
Cl
NH2
N
N
N
N
H
OH
NH2
N
N
N
NH2
OH
N
H
40 41
42 43 44
39
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26
for 28 days. After this time, so-called fungal substrate (SG), which was the
substrate along with the growing mycelium and SMW, i.e. fresh waste remaining
from the substrate after collecting the fungi were obtained. Both the fungal
substrate and SMW were then used to study the utilization of DDT. It was found
that 37% (using SG) and 48% (using SMW) of this pesticide were degraded
during 28 days of incubation. In turn, the mineralization was 4.4% and 5.1%
DDT within 56 days, respectively. Subsequent attempts concerned purification
artificially contaminated with soil DDT. In this case, it was found that SMW
degraded DDT in 40% and 80% in the sterilized and inexperienced soil,
respectively. In such soil samples, during 56 days, the mineralization of DDT
in the amount of 5.1% and 8.0% occurred. The tested pesticide was degraded to
compounds 46, 47 and additionally 2,2-bis-(4-chlorophenyl)-acetic acid 48,
1-chloro-2,2-bis-(4-chlorophenyl)-ethylene 49, 1-chloro-2,2-bis-(4-chlorophenyl)-
ethane 50 (Figure 14) [37].
Figure 14. DDT and its derivatives
Aldrin 51 and its metabolite dieldrin 52 are compounds that permanently
contaminate soil in many parts of the world. Considering the potential risks
associated with these pollutants, an effective method of their degradation is
needed. The P. ostreatus strain was used for biodegradation. As the culture
medium the medium with low nitrogen content (1% glucose, 20 mM sodium
acetate and 1.2 mM ammonium tartrate), medium with high nitrogen content
(1% glucose, 20 mM sodium acetate and 12 mM ammonium tartrate) and broth
with dextrose potato were used. Depending on the type of medium used,
Cl Cl
COOH
Cl Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl Cl
Cl Cl Cl
Cl
Cl
Cl Cl
Cl
Cl
48
49 50
45 46
47
Mushrooms of the Pleurotus genus – properties and application
Biotechnol Food Sci 2019, 83 (1), 13-30 http://www.bfs.p.lodz.pl
27
P. ostreatus eliminated 25%, 72% and 100% of aldrin 51, respectively, during
the 14-day incubation period. The main metabolite was dieldrin 52, besides
9-hydroxydieldrin 53 and 9-hydroxyaldrin 54 were present in the medium. The
proposed biotransformation pathway for aldrin 51 was the epoxidation of
a double bond followed by the hydroxylation of the epoxide ring. P. ostreatus
was also capable of dieldrin 51 degradation. In an environment with a low
nitrogen content, high nitrogen content and in dextrose broth, during the 14-day
incubation period, about 3, 9 and 18% of dieldrin were eliminated, respectively.
In the third variant (dextrose broth), 9-dihydroxydieldrin 53 was detected as
a metabolite. The formation of hydroxylated derivatives is the first step to obtain
less toxic metabolites (Figure 15) [38].
Figure 15. Biodegradation of aldrin
Phthalates are a group of persistent chemicals used primarily as additives to
plastics in order to increase their elasticity. Phthalates are easily released
from plastics into the environment by direct release, migration, leaching and
abrasion as they are not chemically related. Long-chain phthalates, such as
di-(2-ethylhexyl)-phthalate (DEHP) 55, are used in polyvinyl chloride polymers.
DEHP and its metabolite mono-(2-ethylhexyl)-phthalate 56 have toxic effects on
the liver, reproductive system, heart, kidneys and lungs in both primate and
rodents (Figure 16).
The P. ostreatus strain was used for the biodegradation of DEHP. Three types
of medium were used. The control medium consisted of glucose, yeast extract,
mineral salts (KH2PO4, MgSO4·7H2O, K2HPO4, CuSO4·5H2O, FeSO4·7H2O,
MnSO4, ZnSO4·7H2O) and Tween 80. Two other medium contained in addition
to the above ingredients DEHP in 500 mg/L and 1000 mg/L. After adding the
growing mycelium P. ostreatus to the medium, the whole was incubated for
21 days. The highest biomass production was observed in the medium enriched
Cl Cl
Cl Cl
Cl
Cl
Cl Cl
Cl Cl
Cl
Cl
O
Cl Cl
Cl Cl
Cl
Cl
OH
Cl Cl
Cl Cl
Cl
Cl
O
OH
51 52
54
53
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Biotechnol Food Sci 2019, 83 (1), 13-30 http://www.bfs.p.lodz.pl
28
with 1000 mg DEHP, and slightly lower in the medium containing 500 mg
DEHP. It follows that P. ostreatus uses high concentrations of DEHP as a source
of carbon and energy. Phthalate was degraded completely after 504 hours. DEHP
can be metabolized through three pathways; the de-esterification pathway, the
oxidation pathway and the oxidation-hydrolysis pathway, respectively forming
phthalic acid, acetic acid and butanediol [39].
Figure 16. Phthalates
Summary
Mushrooms of the Pleurotus genus can be found in many applications in the
modern world. They are used by the food industry as valuable edible mushrooms.
The pharmaceutical industry can use them as a source of medicinal substances.
Because of them, new oxygen derivatives of terpenoid compounds can be
obtained. What is equally important, these fungi contribute to the purification of
the natural environment from harmful compounds produced by man.
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