Romanian Biotechnological Letters Vol. 16, No. 4, 2011 [601212]

Romanian Biotechnological Letters Vol. 16, No. 4, 2011
Copyright © 2011 University of Bucharest Printed in Romania. All rights reserved
O R I G I N A L P A P E R
 
6364 Investigation of Aspergillus niger growth and activity in a static magnetic
flux density field

Received for publica tion, August 12, 2010
Accepted, July 14, 2011

C. MATEESCU, N. BURUN ȚEA, N. STANCU
National Institute for Research and Development in Electrical Engin eering ICPE-CA,
313 Splaiul Unirii Str.., Bucharest-3, 030138 , Romania, Tel: +[anonimizat]/ext. 115,
Fax: +[anonimizat], e-mail: [anonimizat]

Abstract
Researches focused on the biodegradation of materials have indicated that Aspergillus niger
microscopic fungus is destructor of electrical insulations and other materials used in electrical industry
in all the climatic zones. Static magnetic fields can exert some influence over microorganisms and this
effect depends on many factors such as type and magnitude of magnetic field, type of microorganism, temperature, length/duration of exposure, growth media etc.
The aim of the present study was to investigate the effect of the static magnetic induction field
on the growth and metabolic activity of Aspergillus niger fungus. The results of the study will give a better understanding of biodegradation processes which occur on materials and electrical equipments.
We investigated the growth of th e fungus developed on nutritious Czapek-Dox solid media when
exposed to a magnetic field of 0.50 T and 0.62 T respectively, for a period of 7 days. The exposed
results were compared with those of sham controls , where the fungus developed in the same conditions
as the exposed ones but without applying the magnetic field exposure. In order to assess the growing
and morphology of the fungus colonies, the cultures have been macroscopically examined after 48, 72, 96 and 168 hours respectively, as well as microscopically at the end of the total exposure period.

Keywords: fungus, biodegradation, static magne tic field, electrical equipment

Introduction

Whereas alternating current (AC) transmission lines produce AC (mostly 50 Hz)
electric and magnetic fields, st atic electric and magnetic fields are produced by direct current
(DC) transmission lines whic h is an economical way for power distribution over long
distances. Modern magnetic le vitation (maglev) systems use magnetic flux densities around 1
T directly on the rails [1]. It has to be noticed that AC as well as DC el ectric fields are easily
reduced by all kind of obstacles and materials whereas the magnetic field not and is passing
through buildings, humans, and most of the materials.
Since AC and DC magnetic fields are most likely to penetrate the body, they are the
component of electromagnetic fields that are usua lly studied in relation to the effects on living
systems.
It is well known that mould might cause damage to materials and equipments and
create health problems in warm and humid e nvironments. During the nor mal growth of fungi,
there is an enzymatic secre tion that accelerates a chemi cal transformation of organic
substances such as insulation materials, wood deri vates (paper), some types of seals, coatings,
as well as many other ty pes of materials from the structure of the electrical equipments. Many
minerals are also destroyed by the fungus.
Aspergillus niger is a fungus so widely distributed that it is ubiquitous in nature. This
fungus can spread easily and colonize a wide ra nge of substrates, incl uding wood and plastics
in the components of many devices and equipments. Aspergillus niger fungus may also be
found in compost and other decaying organic material.

C. MATEESCU, N. BURUN ȚEA, N. STANCU

Romanian Biotechnological Letters, Vol. 16, No. 4, 2011 6365 This paper aimed to investigate the growth and activity of Aspergillus niger fungus by
exposing it under two magnetic flux densities (B-f ield), for a total e xposure period of 168
hours. Since the present study is quit e original data on a similar issu e are scarce in literature.
Manoliu et al (2007) [3] inve stigated the development of Aspergillus niger exposed to
a static B-field varying from 40-80 T. The resu lts showed a 1.5 – 2 time s faster growth rate
than in sham controls. Moreover, it has been showed that the B-fiel d exposure can have an
effect on the biodegradability of material s by enhancing the growth rate and the
aggressiveness of the fungus. It has also been noticed that a B-field exposure of more than
350 T may delay the growth of microscopic fungus.
The influence of the B-field exposure on ce llulases and catalase ac tivity in ce llulolytic
fungi Chaetomium globosum and Trichoderma viride cultivated on media with waste from
industry of panification has been investigated too. It has been shown that the activity of these
enzymes was influenced by both studied celluloly tic species and the exposure length to the B-
field [4]. Besides Aspergillus niger fungus, the effect of static magnetic fields has also been
studied at the molecular and cellular levels in bacteria species, yeasts and molds. Moreover,
the growth rate, colony size, gas production, viability and muta tion effects, enzyme activity
and germination of spores [4] have also been investigated. The motivation of our study is double. Firstly, because the Aspergillus niger fungus is
widely spread on electrical equipment in va rious environmental conditions and secondly
because there is a lack of scien tific data on the effect s of static magnetic fi elds on this fungus.

Materials and Methods

For Aspergillus niger growth it has been used Czapek-Dox agar, a synthetic solid
medium, containing sucrose as carbon source a nd nitrate as nitrogen source. On Czapek-Dox
agar, colonies of Aspergillus niger consist of a compact white or yellow basal felt covered by
a dense layer of dark-brown to black colonial heads.
The culture medium was prepared by dissolv ing of the following components into one
liter of distilled water: sucr ose 30 g, sodium nitrate 3 g, po tassium chloride 0.5 g, magnesium
sulfate heptahydrate 0.5 g, iron (II) sulfate heptahydrat e 0.01 g, di-potassium hydrogen
phosphate 1 g and agar 15 g. The suspension wa s brought to the boil in order to dissolve
completely all the ingredients and then was sterilized by autoclaving at 1210C for 15 minutes
[5]. The molten medium was poured into three 7 cm diameter Petri dishes.
The plates were inoculated with Aspergillus niger using a sterile wire. The fungus
which we used for testing was 30 days old and was obtained from our own collection.
The environment conditions for fungus growth were room temperature of 25 ± 20C,
natural light and the humidity provi ded by the culture medium [6].
For studying the efficiency of the B-fiel d, one sham control and two irradiated
(exposed) inoculation plates were used. Whereas the sham inoculated plate was treated in the same way as the irradiated ones but without appl ying the B-field, the two other inoculated plates
were exposed to a B-field of 0.5 T and 0.62 T respectively. T hough the total exposure time was
168 hours, the cultures were pe riodically analyzed after 48, 72, 96 and 168 hours respectively.
After incubations all the cultures were mi croscopically analyzed as regards the
Aspergillus niger sporulation growth, using an optical inverted microscope type Nikon
Eclipse Ti-E fitted with a confocal system Ec lipse C1si. The microscopic examination of the
fungus was performed in bright field with a magnitude of 40 X.
In order to make a comparative analysis of Aspergillus niger growth under different
static magnetic flux densities, two magnetic sy stems have been calculated and designed for

Investigation of Aspergillus niger growth and activity in a static magnetic flux density field

6366 Romanian Biotechnological Letters, Vol. 16, No. 4, 2011 performing exposures to B-field of 0.5 T and 0.6 2 T. These magnetic syst ems consisted of the
following components:
a. Magnetic circuit made of steel type OL 35; b. Permanent magnets, made of magnetic all oy based on NdFeB, having the following
magnetic field characteristics: Br = 1.2 T, Hcb = 970 kA/m, (BH)
max = 35 MGsOe,
respectively;
c. Polar pieces made of steel type OL 35. The exposure strength of the B-field in air has been performed by simulation of
magnetic fields using a magnetic calculation soft type FEM (Finit Element Method).

Results and discussions

For the investigations of the effect of a static B-field on the mycelial growth and
conidia formation, the plates were examined af ter an incubation period of 48, 72, 96 and 168
hours respectively. Figures 1-4 (a,b,c) show the Aspergillus niger growth without B-field
exposure (sham control), under a B-field exposure of 0.5 T and of 0.62 T, for 48, 72, 96 and
168 hours respectively.
During the first 48 hours we observed that the non-exposed fungus has grown faster
than the two other samples which were exposed to the B-field. It means that after an
incubation of 48 hours, the growth of Aspergillus niger was characterized by the development
of small but compact colonies with dense sporul ation, spread from the inoculated point to the
whole surface of the culture medium (Figure 1 a). The fungus exposed to the B-field produced
less but larger colonies, with strong sporulation. The colonies are not spread on the whole
surface of the culture medium (Figures 1b, 1c).

a b c
Fig 1. (a,b,c) Aspergillus niger growth after 48 hours of incubation (a -without magnetic field;
b – magnetic field of 0.5T; c – magnetic field of 0.62T)

After a B-field exposure of 72 hours, th e mould followed an atypical growth,
characterized by about 20 larger and bombastic colonies ha ving white-yellowish normal
aspect and very few dark-brown colonial head s. A stronger B-field exposure resulted in a
larger but rarer colony formati on in the culture medium. Thus, for the plate exposed to a B-
field of 0.5 T (Figure 2b), we observed more bu t smaller colonies which tend to join each
other, comparing to the sample exposed in B- field of 0.62 T (Figure 2c). By comparing the
0.5 T (Figure 2b) and the 0.62 T exposure results, we observe in the first case more but
smaller colonies which tend to stick together than in the second case.

C. MATEESCU, N. BURUN ȚEA, N. STANCU

Romanian Biotechnological Letters, Vol. 16, No. 4, 2011 6367

a b c
Fig 2. (a,b,c) Aspergillus niger growth after 72 hours of incubation (a -without magnetic field; b – magnetic
field of 0.5; c – magnetic field of 0.62T)

After 96 hours of incubation, some notches or cuts be came visible on the swollen
surface of the colonies. They ar e more explicit for the stronger B-field of 0.62 T (Figure 3c).
These notches did not arise when the B-field was not applied.

a b c
Fig 3. (a,b,c) Aspergillus niger growth after 96 hours of incubation (a -without magnetic field;b – magnetic field
of 0.5T; c – magnetic field of 0.62T)

After an incubation period of 168 hours (at the end of testing), we observed a
relatively homogenous growth of the fungus in the plate not exposed to the B-field (Figure
4a). The colonies became completely black on the whole surface of the culture medium.
The sample exposed to the strongest B-fiel d of 0.62 T (Figure 4c) showed intensively
black colored and large colonies. In this case the black colonial heads are denser as compared
to the fungus developed in cultur es not exposed to a B-field . This atypical growth does not
cover the entire surface of the Pe tri dish. The sample exposed in the B-field of 0.5 T (Figure
4b) shows an intermediary aspect between the two plates.

a b c
Fig 4. (a,b,c) Aspergillus niger growth after 168 hours of incubation (a -without magnetic field; b – magnetic
field of 0.5T; c – magnetic field of 0.62T)

Investigation of Aspergillus niger growth and activity in a static magnetic flux density field

6368 Romanian Biotechnological Letters, Vol. 16, No. 4, 2011 Figure 5 shows a microscopic photograph of ra diate conidial head and brown-colored
round-shaped unicellular conidia of Aspergillus niger.

Fig. 5. Micrograph of Aspergillus niger conidia with a full-fi eld on the left and a detail shot on the right

Conidia in chains or detach ed and dispersed can be ob served in this microscopy
image. Single or paired conidia may rese mble yeast cells. The size of spores of Aspergillus
niger ranges from 2 to 4 microns.

Conclusions

The effect of a static magnetic flux density on the growth and activity of Aspergillus
niger have been macroscopically and microscopi cally investigated by means of two exposure
strengths. It is concluded that the static magnetic field produces an atypical growth of the
fungus that is characterized by less and swolle n, bombastic colonies which did not spread on
the entire surface of the culture medium. From the comparison between the exposed and the
sham, we conclude that the magnetic field is an efficient inhibitor of th e surface growth of the
fungus. The validation or practical ap plication of the present study lies in the fact that the
results can be used for devel oping magnetic field sources/methods that are able to reduce or
eliminate bio-damage of components of electrical equipments or installations and materials
which are sensitive to Aspergillus niger and perhaps to other fungi.

References

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3. A. MANOLIU, L. OPRICK, D. CREANGA, The influence of the static magnetic field (SMF) on some
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zapek_dox_agar.pdf
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