Zbornik Matice srpske za prirodne nauke / Proc. Nat. Sci., Matica Srpska Novi Sad,
¥ 113, 227—233, 2007
UDC 546.23:579.6
J e l e n a V u k o j e v i ã, M i r j a n a S t a j i ã,
Sonja Duletiã-Lauševiã
Institute of Botany, Faculty of Biology, University of Belgrade,
Takovska 43, 11000 Belgrade, Serbia
e-mail: stajicm@bfbot.bg.ac.yu, vjelena@bfbot.bg.ac.yu
ABILITY OF PLEUROTUS ERYNGII MYCELIUM TO
ABSORB SELENIUM DEPENDING ON THE SELENIUM
SOURCE AND CONCENTRATION IN MEDIUM
ABSTRACT: The aim of our research was to investigate the influence of three different inorganic Se sources, added to the synthetic medium, on the Pleurotus eryngii mycelium ability to absorb and retain this microelement. All investigated P. eryngii strains were
good Se absorbers from the media enriched with all studied Se sources. Strain HAI 711,
which was cultivated in the Na2SeO4-enriched medium at Se concentration of 1.0 and 1.3
mgl—1, respectively, showed extraordinarily high Se concentrations in the mycelium (725
mgg—1 of dry weight and 575 mgg—1 of dry weight, respectively).
KEY WORDS: Pleurotus eryngii, mycelium, selenium absorption
INTRODUCTION
Pleurotus eryngii (DC.: Fr.) Quél is economically highly praised species
due to its nutritional and medicinal value. This species has: anti-hypertensive
effect, because of low sodium and great potassium concentration; antioxidant
effect, because of the presence of phenolic compounds; anti-hypercholesterolic
effect, due to a significant amount of dietary fibers, b-glucans, chitin, and chitosan; anti-hyperglycemic, immunomodulating, antitumor, antibacterial, antiviral, antifungal, antiinflammatory, and antiosteoporotic effects (M a n z i et al.,
1999; 2004; M a n z i and P i z z o f e r r a t o, 2000). Although selenium (Se)
is not an essential microelement for yeast and plants (F l o h é et al., 2000), it
plays an essential nutritional role in some animals and humans. Se is an integral component of several enzymes, selenoprotein P and W, albumin, and
so-called 15 kDa selenoprotein and selenoprotein N, whose functions are still
elusive (B i r r i n g e r et al., 2002). In accordance with the roles of Se dependent-enzymes and proteins, that trace element is antioxidant and an antimuta227
genic agent, which prevents the malignant transformation of normal cells and
the activation of oncogenes (S t a p l e t o n, 2000).
Pleurotus species have the ability to absorb this microelement from medium and may present an excellent dietary Se source (S t a j i ã et al., 2002;
D u l e t i ã - L a u š e v i ã et al., 2005).
The aim of this research was to investigate the influence of three different
inorganic Se sources, added to the medium in different concentrations, on the
mycelium ability to absorb it.
MATERIALS AND METHODS
The investigated P. eryngii strains and their origin are presented in Table
1. These cultures were obtained from the culture collection of the Institute of
Evolution, University of Haifa (HAI), Israel.
Tab. 1 — Investigated Pleurotus eryngii strains
Scientific name
of species
HAI number
of strains
201
356
507
616
711
716
728
Ukrainian SSR, Kherson region, Chaplinka
district, Askania-Nova, on Stipa sp.
Israel, Menahemya, on Ferula sp.
Israel, Gevaot Merar, near Gedera, on Ferula sp.
Cultivated strain, Hawaii, Nextlab
Israel, Tabor, on Ferula sp.
Israel, Tel Hazor, on Ferula sp.
Israel, Gilboa, on Ferula sp.
Israel, Lahav, on Ferula sp.
555
Israel, Sataf, on Ferula tingitana L.
193
P. eryngii (DC.: Fr.)
Quél. var. eryngii
P. eryngii var. tingitanus
Lewinsohn et al.
Origin of strains
Selenium was used in the forms of sodium selenite (Na2SeO3), sodium selenate (Na2SeO4), and selenium dioxide (SeO2), in the concentrations of 0.3
mgl—1, 0.7 mgl—1, 1.0 mgl—1, and 1.3 mgl—1. Synthetic medium of the following composition: glucose, 10.0 gl—1; NH4NO3, 2.0 gl—1; KH2PO4, 0.8 gl—1;
Na2HPO4 x 7H2O, 0.75 gl—1; MgSO4 x 7 H2O, 0.5 gl—1; yeast extract, 2.0 gl—1,
pH 6.0 (50 ml per flask), was inoculated and incubated at room temperature
(22 ± 2°C), on the rotary shaker at 180 rpm, for 28 days. The medium without
Se was used as the control. Three repetitions for each Se source and concentration per strain were performed. After the cultivation period, mycelia were
filtrated and dried at 30°C during the night. For Se extraction, dry mycelia
were treated with: 70% of nitric acid, 70% of nitric acid + 70% of perchloric
acid (3:1), and 6 M HCl (37%), in a mineralizator at 120°C. Se concentrations
in mycelia were measured by graphite furnace Atomic Absorption Spectrometer (VARIAN, Australia).
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RESULTS
Na2SeO3 was a good Se source for the absorption by mycelium and incorporation of Se compounds in the cell, in all investigated P. eryngii strains
(Fig. 1).
Fig. 1 — Se content in mycelia (mgg—1 of dry weight) of investigated Pleurotus eryngii
strains cultivated in medium with Na2SeO3 as Se source
Fig. 2 — Se content in mycelia (mgg—1 of dry weight) of investigated Pleurotus eryngii
strains cultivated in medium with Na2SeO4 as Se source
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Among the investigated strains of P. eryngii var. eryngii, two groups
were distinguished according to their ability to absorb Se from Na2SeO4-enriched medium, and to retain it. Strains HAI 201 and HAI 507 fit into the first
group, where Se content in the mycelium decreased, compared to the control,
at the Se concentration of 0.3 mgl—1, while in the presence of higher Se concentrations in the medium, mycelium content increased. In the second group,
other investigated P. eryngii var. eryngii strains showed more or less increase
in Se concentration in the mycelium with its addition to the medium. Strain
HAI 711, which was cultivated in the Se-enriched medium with 1.0 and 1.3
mgl—1, respectively, showed extraordinarily high Se concentrations in the mycelium (725 mgg—1 of dry weight and 575 mgg—1 of dry weight, respectively).
However, in P. eryngii var. tingitanus HAI 555, it was not noted only a decrease in Se concentration in the mycelium, compared to the control, but also
its absence when it was present in the medium at the concentration of 0.7
mgl—1 (Fig. 2).
SeO2, as well as Na2SeO3, were shown as good sources for Se absorption
and retention by mycelia of P. eryngii strains. All investigated P. eryngii var.
eryngii strains, as well as P. eryngii var. tingitanus, easily absorbed Se from
medium, when it was present at the concentration of 1.3 mgl—1, except strain
HAI 201 where the highest concentration of absorbed Se was at its medium
concentration of 0.7 mgl—1 (Fig. 3).
Fig. 3 — Se content in mycelia (mgg—1 of dry weight) of investigated Pleurotus eryngii
strains cultivated in medium with SeO2 as Se source
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DISCUSSION
The obtained results showed that all the investigated P. eryngii strains
were good Se absorbers from the medium enriched with all studied Se sources.
However, the strains had different abilities to absorb and retain Se in the
mycelium, and some of them had lower Se concentration in mycelium growing
in Se-enriched medium, than in the control one. These may be explained by
the following facts:
— the increased Se concentration in the control could be explained by
using the wort agar medium for preserving the P. eryngii cultures, concerning
that wort itself is rich in Se, containing between 0.24 and 0.66 mg/kg of dry
weight, depending on the Se concentration in soil (M i h a i l o v i ã, 1996);
— all organisms can assimilate selenites and selenides, while only terrestrial plants and bacteria can assimilate selenates (B i r r i n g e r et al., 2002);
— the absorption of Na2SeO3 from aquatic environments is a passive
process distinguished from the absorption of Na2SeO4 (B a r c e l o u x, 1999);
— the resorption of Se from selenites is 3 times higher than from selenates (B u t l e r and P e t e r s o n, 1967);
— for the Se incorporation into selenoproteins, it needs the absorbed selenites or selenates to be reduced to the selenide form. As distinguished from
selenates, which are reduced to selenites, firstly in presence of ATP sulfurylase, selenites are readily reduced to selenide by flavine-dependent disulfide
reductases (B i r r i n g e r et al., 2002). SeO2 in the presence of H2O gives selenious acid, which with 4 molecules of glutathione, and by releasing 3 molecules of H2O, gives selenoglutathione which is reduced to selenide (S p a l l h o l z, 1994). The obtained selenide will go either into biosynthesis of selenocysteine which will be incorporated into selenoproteins, or into methylation
to methaneselenol or dimethyl selenide which lead to excretion or volatilization of Se (C o m b s and G r a y, 1998). On the other hand, both synthesized
selenoproteins are degraded after a certain period of time, and selenocysteine
may go into one of three metabolic pathways (R o o s e b o o m et al., 2001):
(i) oxidative deamination, which products are NH3, pyruvate, and HSeO3 —
that may oxidize to selenate; (ii) b elimination, which products are selenol,
pyruvate, and NH3; (iii) selenoxidation, which products are selenious acid and
2 — aminoacrylic acid that hydrolyse into pyruvate and NH3.
Unfortunately, knowledge on Se metabolism in fungi is limited, because
investigations have only been done with yeasts. The literature data about Se
form in filamentous fungi is lacking. In the previous studies of yeast grown in
Se-enriched medium, it was reported that yeast contained 15.7% of elemental
Se, 5.5% of inorganic, and 76.8% of organic Se (Ÿ i v k o v i ã, 1989).
S h a m b e r g e r (1985) studied the effects of sodium selenite, sodium
selenide, and sodium selenate on suppressing spontaneous mutagenesis at lysine and histidine locus in yeast. Contrary to selenite and selenide, which completely suppressed mutagenesis, selenate inhibited mutagenesis only at the lysine locus, which needed lower quantities of selenite and selenide than the histidine locus mutagenesis. Do these results show that yeast has a lower ability
to use selenate than selenide and selenite from media?
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Capacity of Se absorption by mycelium, also depends on medium where
it was grown. This was shown by previous experiments with P. ostreatus HAI
387 (S t a j i ã et al., 2002) and Ganoderma lucidum (D u l e t i ã - L a u š e v i ã et al., 2005). Se content in mycelium of both investigated species was
significantly higher at their cultivation in potato-dextrose Se-enriched medium
with Na2SeO3, than in malt medium, and especially in synthetic medium with
the same Se source. Potato-dextrose medium was also better for production of
mycelial biomass, compared to the synthetic medium.
Results obtained here set new goals for further investigations: Se metabolite pathways in higher Basidiomycetes, the forms of absorbed Se in mycelium, as well as finding the best cultivation medium, and Se source for its absorption and incorporation of the organic Se compounds in the cell.
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SPOSOBNOST MICELIJE PLEUROTUS ERYNGII DA APSORBUJE
SELEN U ZAVISNOSTI OD IZVORA I KONCENTRACIJE
SELENA U MEDIJUMU
Jelena Vukojeviã, Mirjana Stajiã, Sowa Duletiã-Lauševiã
Institut za botaniku, Biološki fakultet Univerziteta
u Beogradu, Takovska 43, 11000 Beograd, Srbija
e-mail: stajicm@bfbot.bg.ac.yu, vjelena@bfbot.bg.ac.yu
Rezime
Ciq istraÿivawa je bio prouåavawe uticaja tri razliåita neorganska izvora selena dodata u sintetiåku hranqivu podlogu na sposobnost micelije P.
eryngii da apsorbuje i zadrÿava ovaj mikroelement. Svi prouåavani P. eryngii
izolati su dobro usvajali selen iz podloge obogaãene odabranim izvorima selena. Soj HAI 711 koji je bio kultivisan u Na2SeO4 — obogaãenoj podlozi pri
koncentraciji selena od 1.0 odnosno 1.3. mgl–1 imao je izuzetno visoku koncentraciju selena u miceliji (725 mgg–1 suve mase odnosno 575 mgg–1 suve mase).
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