Mycotoxin production in Cladosporium species influenced by temperature regimes

Abstract

Cladosporium is a mycotoxin secreting and potentially pathogenic fungus frequently occurring in outdoor environments. In this study prevalence of Cladosporium species in the atmosphere within and around Riyadh city was monitored and production of mycotoxin by the isolates was assessed at different incubation temperatures under in vitro conditions. Two hundred air samples were collected from twenty locations of Riyadh. Only 20 samples were found to carry Cladosporium inoculum, belonging to two species, namely, C. cladosporioides and C. sphaerospermum. Crude extracts of the fungal cultures in acetone were scanned by spectrophotometry for presence of mycotoxins. It was noticed that cultures grown at lower temperature (10 and 15°C) yielded higher amount of mycotoxins as compared to cultures incubated at higher temperatures (20-30°C). HPLC assays of the extracts revealed five compounds corroborating with spectrophotometry findings of higher levels at low temperature. LC/GC-MS analysis revealed several compounds known for diverse activities.

Full text

JOURNAL OF PURE AND APPLIED MICROBIOLOGY, October 2014. Vol. 8(5), p. 4061-4069
* To whom all correspondence should be addressed.
E-mail: mbmoslem@ksu.edu.sa
Mycotoxin Production in Cladosporium Species
Influenced by Temperature Regimes
Mohannad Abdullah Alwatban1, S. Hadi2 and M.A. Moslem2*
1King Abdulaziz City for Science and Technology (KACST), P. Box 6086,
Riyadh 11442, Saudi Arabia.
2Department of Botany and Microbiology, College of Science, P. Box 2455,
King Saud University, Riyadh – 14451, Saudi Arabia.
(Received: 30 September 2014; accepted: 01 October 2014)
Cladosporium is a mycotoxin secreting and potentially pathogenic fungus
frequently occurring in outdoor environments. In this study prevalence of Cladosporium
species in the atmosphere within and around Riyadh city was monitored and production
of mycotoxin by the isolates was assessed at different incubation temperatures under in
vitro conditions. Two hundred air samples were collected from twenty locations of Riyadh.
Only 20 samples were found to carry Cladosporium inoculum, belonging to two species,
namely, C. cladosporioides and C. sphaerospermum. Crude extracts of the fungal cultures
in acetone were scanned by spectrophotometry for presence of mycotoxins. It was noticed
that cultures grown at lower temperature (10 and 15°C) yielded higher amount of
mycotoxins as compared to cultures incubated at higher temperatures (20-30°C). HPLC
assays of the extracts revealed five compounds corroborating with spectrophotometry
findings of higher levels at low temperature. LC/GC-MS analysis revealed several
compounds known for diverse activities.
Key words: Airborne fungi; Cladosporium; Environment; Mycotoxin.
Cladosporium is a ubiquitous fungus
prevailing at a comparatively high frequency in
the outdoor environment1, 2,3. Habit of this fungus
is largely saprophytic inhabiting dead organic
matter and often contaminating the food material;
but it may be pathogenic as well causing clinical
conditions of diverse nature in humans1.
Cladosporium species are known to secrete
mycotoxins which are believed to be causal agents
for allergies4, Cutaneous/sub-cutaneous
infections5, 6, 7, 8, Pulmonary mycosis 4, 5, 9,
phaeohypho mycosis10 etc. Some of these
manifestations may be life threatening. As such,
this airborne fungus has significant repercussions
for human health.
Pathogenicity and virulence of
Cladosporium species, like other pathogenic fungi,
owe their degree mainly to the nature and level of
mycotoxins produced by these organisms in
combination with the response of corresponding
host11, 12, 13. Major mycotoxins produced by
Cladosporium species are cladosporin14,
isocladosporin15,emodin16, epi- and fagi-
cladosporic acid17, and ergot alkaloids18. Besides
these, over a dozen molecules have been detected
as secondary metabolites of Cladosporium
species; many of which have shown toxigenic
activity19. Apart from their involvement in
pathogenic conditions of humans, animals, and
plants, some of the mycotoxins have been found
to possess significant pharmaceutical properties

J PURE APPL MICROBIO, 8(5), OCTOBER 2014.
4062 ALWATBAN et al.: MYCOTOXIN PRODUCTION IN Cladosporium SP
as well14, 20, 21, 22. Their dual role as agents of
pathogenesis and pharmaceuticals makes the
mycotoxins interesting entities to study in greater
details and from different viewpoints.
Present study was focused on assessing
the ability of air borne Cladosporium species to
produce different secondary metabolites under in-
vitro conditions at variable temperature.
MATERIALS AND METHODS
Collection of samples and preparation of pure
culturesIn all, 200 air samples were collected from
40 sites transecting through northern, southern,
eastern, western, and central region of Riyadh city
during summer season. For each sample of air, single
plate of potato dextrose agar (PDA) medium was
inserted into the air sampler (SAS HiVac Petri-
17407). The instrument was set for suction at 80
cuft minute-1 and air was sucked for 1 minute for
each sample. Mean temperature was 44.2 °C and
mean relative humidity (RH) was 23 during the
collection of samples.
Plates taken directly from the air sampler
were incubated at 28°C for 48 hours. During this
period many colonies appeared in the plates.
Immediately after the appearance, tiny portion of
each colony was transferred to fresh medium on a
separate plate. Procedure was repeated till
individual pure colonies were obtained.
Identification of Cladosporium isolates
Sixteen cultures tentatively identified as
Cladosporium on the basis of microscopic
examination were sent to Assiut University
Mycological Centre (AUMC) at Assiut, Egypt for
confirmation and species identification; where ten
were identified as C. sphaerospermum and six as
C. cladosporioides. Single most actively growing
isolate of each species was selected for onward
experimentation.
Incubation of Cladosporium isolates at different
temperatures
Pure cultures of C. cladosporioides and
C. sphaerospermum were incubated on potato
dextrose agar (PDA) medium at 10, 15, 20, 25, 30°C
for 2 weeks.
Extraction of mycotoxins
Two weeks after incubation at respective
temperatures, mycotoxins were extracted from the
fungal mat using a procedure modified from 23, 24, 25.
Mycelial mat along with the underlying medium
measuring 1.5 cm in diameter was punched out
with a piece of steel tube, taking care to maintain
uniformity of the quantity of medium attached with
cultures. The collected mass was homogenized in
70% methanol and volume was made up to 5 ml.
After stirring the homogenate for 2 hours at room
temperature, it was filtered through Whatman filter
No1. Methanol was evaporated under vacuum and
the volume was made up to 5 ml with 0.1M
phosphate buffer (pH 8.5). After shaking for two
minutes, the crude extract was partitioned with 50
ml ethyl acetate in a separating funnel. Partitioning
was done three times. Ethyl acetate phase was
removed by vacuum and pH of the aqueous phase
was adjusted to 2.5 with 1N HCl. The remaining
aqueous solution was partitioned with 50 ml diethyl
ether three times. Diethyl ether phase was collected
and dried over sodium sulfate. After evaporating
diethyl ether completely under vacuum, the residue
was dissolved in 1 ml methanol and was stored at
4°C.
Spectrophotometric assays
Spectrophotometric assays were done to
verify the presence of mycotoxins before
separation of molecules by high performance liquid
chromatography (HPLC) and their characterization
by liquid chromatography-mass spectrophotometry
(LC-MS) and gas chromatography-mass
spectrophotometry (GC-MS). Extracts of the isolates
selected as above were used for spectrophotometric
assays. Since the known Cladosporium toxins
were not available in the market which could be
used as standards, quantification of individual
toxins by spectrophotometry was not possible. In
the absence of standards, only a comparative
assessment for the level of total toxins in the
extracts under different treatments was made in
terms of absorbance values.
Methanol extracts were dried under
vacuum and the residue was re-dissolved in 1 ml
of acetone. For detecting the presence of toxins
acetone samples, were scanned for absorbance at
540 nm in a spectrophotometer (Gene Quant Pro,
Amersham Biosciences, USA). Solvent acetone
was used as blank.
Separation of mycotoxins by HPLC
In the absence of standards, only a

J PURE APPL MICROBIO, 8(5), OCTOBER 2014.
4063ALWATBAN et al.: MYCOTOXIN PRODUCTION IN Cladosporium SP
comparative analysis of number and level of
mycotoxins produced at different temperatures of
incubation was conducted by HPLC using
previously tested methods23, 24, 25. Extracts of the
same isolates as used for photometry were used
for HPLC analysis. Analysis was performed on
Finnigan Surveyor Plus (Thermo Scientific, USA)
HPLC system. An octadecylsilane (C-18) column
of dimension: 250 x 4.6 mm with 3µm particle size
(Thermo Scientific) was used for separation of
constituent molecules. Methyl alcohol-water (45:55
– pH 2.5) was used as mobile phase and 5µl of
sample was injected into the system for each run.
Column temperature of 25°C and flow rate of 0.8
ml/min were maintained throughout the analysis.
The eluate was scanned at a wave length of 265
nm with a UV detector.The analysis was performed
thrice and each set of data was treated as a replicate.
LC-MS analysis
Following Pais and Knize26, Paiset al.27,
and Galceran et al.28, LC-MS analysis of samples
was done on a triple–quadrupole mass
spectrometer (3U, Waters Corp. USA) in electro-
spray negative ionization mode. Other conditions
were as follows: voltage (capillary: 3.5 kV, cone: -
40 V, and extractor: -3 V); temperature (source:
120°C, desolvation: 350°C); gas flow (desolvation:
600 lh-1, cone: 60 lh-1). Data acquisition was done
with MassLynxV4.1 software.
GC-MS analysis
For non-polar and volatile compounds,
gas chromatography-mass spectrometry (GC-MS)
is a better suited detection technique, which ideally
combines the advantages of the high separation
efficiency of capillary GC with high sensitivity and
selectivity of MS detector.
Following Pais and Knize26, a GC unit
(model Trace GC Ultra, Thermo Scientific Co.) with
auto sampler (AI3000) and MS unit (TSQ Quantum
GC, Thermo Scientific Co.) was used with a column
of dimensions: 60 m x 0.25 mm x 0.25 µm film (Thermo
TR-1). Following instrument parameters were set
for the analysis: inlet temperature: 275°C, split
flow:50 ml min-1, injection volume: 0.5 µl, carrier
gas: helium, carrier gas flow: 1.0 ml min-1, and MS
transfer line temperature: 250°C. Data was acquired
with Xcaliber software.
Statistical procedures
During spectrophotometry, five sets of
absorbance readings were recorded for each
treatment and variation was estimated by standard
deviations of the means. HPLC analysis was
conducted in three replicates and variance was
calculated by F test following which, means were
separated by least significant difference (LSD)
at t5%.
RESULTS
Most of the samples developed fungal
colonies on PDA within 48-72 hours and pure
cultures could be obtained after a few subcultures.
Only 16(8.0%) air samples out of 200 collected from
all over the city of Riyadh developed Cladosporium
colonies on PDA plates, besides other fungi. Seven
of these samples carried C. sphaerospermum Penzig
only and three developed only C. cladosporioides
(Fresenius) deVries, while remaining six showed
both these species.
Mycotoxin level at variable temperature detected
by spectrophotometry
Considering absorbance to be a function
of mycotoxin concentration, it was noticed (Table1)
that C. cladosporioides cultures incubated at lower
temperatures of 10 and 15 °C produced toxins in
greater quantity (absorbance: 0.703 and 0.739
respectively) as compared to cultures grown at
higher temperatures of 20, 25, and 30°C
Table 1. Absorbance values of crude extracts of
Cladosporium isolates grown at variable temperature
Incubation Absorbance (540 nm)
Medium Temperature(°C) C. cladosporioides C. sphaerospermum
PDA 10 0.703±0.002 0.659±0.002
15 0.739±0.003 0.702±0.002
20 0.049±0.001 0.710±0.002
25 0.065±0.001 0.061±0.001
30 0.053±0.001 0.090±0.001

J PURE APPL MICROBIO, 8(5), OCTOBER 2014.
4064 ALWATBAN et al.: MYCOTOXIN PRODUCTION IN Cladosporium SP
Table 2. Peak characteristics of the five compounds detected in HPLC analysis of crude extracts of Cladosporium isolates grown at variable temperature
Fungal Incubation 1st peak 2nd peak 3rd peak 4th peak 5th peak
genotype temp.(°C) Ret. Height Area Ret. Height Area Ret. Height Area Ret. Height Area Ret. Height Area
Time Time Time Time Time
(min) (mAU)†(mAU.S)‡(min) (mAU)†(mAU.S)‡(min) (mAU) (mAU.S)‡(min) (mAU) (mAU.S)‡(min) (mAU) (mAU.S)‡
C. 10 6.32 9.21 106.84b7.36 98.58 1662.48a9.24 38.78 123.13bND ND ND 14.48 10.82 207.53a
cladosporioides 15 6.34 10.49 126.15a7.36 98.62 1662.31a9.25 49.84 158.24cND ND ND 14.36 9.85 188.92b
20 6.31 9.56 112.81b7.33 76.52 1124.36b9.28 50.23 159.48c13.22 11.82 211.58a14.29 10.91 209.25a
25 6.32 7.52 88.74c7.34 75.65 1096.92b9.22 53.63 170.26a13.64 12.02 215.05a14.29 11.06 212.19a
30 6.34 7.54 87.46c7.35 68.47 814.54c9.27 56.22 162.64ac 13.23 12.09 216.41a14.19 11.36 217.88a
LSD t5% 8.42 LSD t5% 68.65 LSD t5% 9.25 LSD t5% 6.28 LSD t5% 10.90
C. 10 6.34 11.23 139.25a7.35 81.46 1569.24c 9.23 42.26 134.18d 13.21 12.84 229.84a14.22 9.68 185.67b
sphaerospermum 15 6.32 11.17 138.51a7.37 92.34 1662.12b 9.27 46.52 147.70c 13.18 12.35 221.06b14.18 10.25 196.60ab
20 6.31 8.45 100.56b7.37 97.57 1786.70a 9.24 54.23 172.19b 13.22 12.86 230.19a14.26 10.84 207.92a
25 6.32 7.21 81.75c7.31 78.65 1245.14d 9.29 56.15 178.27b 13.21 10.21 182.76cND ND ND
30 6.31 7.24 83.98c7.33 78.42 1186.56d 9.22 59.22 188.02a 13.24 10.32 184.72cND ND ND
LSD t5% 7.86 LSD t5% 76.54 LSD t5% 8.82 LSD t5% 7.35 LSD t5% 9.86
Values followed by the same superscript are not significantly different from each other at P≤0.05 † Mille absorbance units Height x ½ width of peak base in seconds ND: Not detected
(absorbance: 0.049, 0.065, and 0.053 respectively).
Similarly, C. sphaerospermum cultures also
produced higher levels of mycotoxins at 10, 15,
and 20°C (absorbance: 0.659, 0.702, and 0.710
respectively) as compared to cultures grown at 25
and 30°C (absorbance: 0.061 and 0.090
respectively).
Mycotoxins at variable temperature detected by
HPLC HPLC analysis revealed five compounds
in the extract of the two Cladosporium species.
Figure 1 shows the chromatograph for the extract
from C. cladosporioides cultures incubated at
25°C. First compound showed a retention time of
6.31-6.34 minutes; the peak attained a height of
7.52 to 11.23mAU (mille absorbance units) with
corresponding peak areas ranging from 81.75 to
139.25 mAU-seconds for the two species under
different regimes of incubation (Table 2). Second,
third, fourth, and fifth peaks appeared between
7.31-7.37, 9.22-9.29, 13.18-13.24, and 14.18-14.48
minutes respectively. Ample variability was noticed
in the height and area of the peaks representing
different incubation temperatures. Comparatively
larger peak areas symbolizing greater quantities
were noticed for first and second compounds at 10
and 20ºC. Conversely, third compound showed
larger peak areas at higher temperatures. Fourth
peak was absent in extracts of C. cladosporioides
incubated at 10-15ºC; while fifth peak did not
appear in extracts of C.sphaerospermum incubated
at 25-30ºC. Cumulatively, incubation at 20°C
supported the production of all the five compounds
by both the species. In the absence of standards
for known mycotoxins produced by Cladosporium
species, identity and concentration of these
compounds could not be ascertained by the HPLC
procedures.
Molecules detected by LC/GC-MS
Seven molecules with known anti-fungal
activity were detected in LC/GC -MS analysis of
different Cladosporium samples (Table 3). Of
these, cladosporin, isocladosporin, cladosporid A,
and pentanorlanost-3β-diolwere present in
samples of both the species incubated at all
temperatures. Mycoversillin and epidechloro
griseoful-vin were produced by both the species
of Cladosporium only when incubated at low
temperature of 10-15°C and 10-20°C respectively.
Octaketideacetate diol, on the other hand, was not

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4065ALWATBAN et al.: MYCOTOXIN PRODUCTION IN Cladosporium SP
Table 3. Molecules detected by LC/GC–MS at variable incubation temperature
Molecules C. cladosporioides C. sphaerospermum Known activity
with Mass Incubation Incubation Anti Anti Other Plant
(Arranged temperature (°C) temperature (°C) fungal bacterial toxicities growth
regulators
alphabetically) 10 15 20 25 30 10 15 20 25 30
Altenuisol (278) ++++++++++ - -+ -
Calphostin A (310, 311) ++++++++++ - -+ -
Calphostin C ((310, 311) ++++++++++- -+-
Calphostin D (310 (311) ++++++++++ - -+-
Cladospolid A (308) +++++++++++ - -+
Cladospolid B ((308) ++++++++++ - - -+
Cladospolid C (309) ++++++++++- - - +
Cladosporol (307) ++++++++++ - -+ -
Cladosprin (314) +++++++++++ - -+
Collectodiol (296-297) ++++-+++- - - -+-
Deacetylyanuthone A (123) + ----+++---+--
Emodin (86) ++++++++++ - -+ -
Epidechlorogriseofulvin (318) + + - - - + + + - - - - + -
1-Hydroxyyanuthone A (124) + ----++----+--
Isocladosporin (313) +++++++++++ - -+
Isoharzandione (240) + ----+----+---
Koninginin A ((241-242) ++++-++++- - - -+
Mollicellin C (302) - - - + - - - - + - - + - -
Mycoversillin (97-99) + + - - - + + - - - + - - -
Octaketide-acetat diol (322) - + + + + - - + + + + - - -
Ophibolin K (102) + ----++----+--
Pentanorlanost-3β-diol (312) +++++++++++ - - -
Pergillin (114) - - - + + - - - + + - - - +
Ustic acid (119-120) - + + + + - - + + + - - + -

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4066 ALWATBAN et al.: MYCOTOXIN PRODUCTION IN Cladosporium SP
produced by either of the species at 10°C and
appeared only at higher temperatures.
Four known anti-bacterial compounds
were found in the samples of Cladosporium extracts
(Table3). Out of these, deacetyl-yanuthone A, 1-
hydroxyyanuthone A, and ophiobolin K were
produce only at lower temperatures; while
mollicellin C appeared at moderate incubation
temperature of 25°C in cultures of both the species.
Besides anti-fungal and anti-bacterial
compounds, some molecules known to possess
other types of toxicities were also detected in GC/
LC-mass analysis of the samples (Table3). In all 9
such molecules were noticed in the samples. Of
these, altenuisol, calphostin A, C, D, cladosporol,
and emodin, all inhibitors of protein kinase C, were
produced at all incubation temperatures by both
the species. Collectodiol and
epidechlorogriseofulvin showed a tendency of
production at lower temperatures; and conversely,
ustic acid appeared at higher temperatures only.
Some compounds which are known to
have plant growth regulatory activity were also
found in the samples (Table 3). Four of these
compounds, namely cladosporin, isocladosporin,
koninginin A, and pergillin fall in the category of
plant growth inhibitors; while three forms of
cladospolid (A, B, and C) found in our samples are
known to have plant growth regulatory activity.
These three forms of cladospolid, cladosporin,and
isocladosporin were produced by both the species
of Cladosporium at all temperatures of incubation.
Koninginin was absent at 30°C and pergillin did
not appear at lower temperatures of 10-20°C.
DISCUSSION
Occurrence of Cladosporium in only 8%
of the samples collected from all over the city
indicates that this fungus occurs at a low
frequency in the atmosphere of Riyadh. In a similar
study elsewhere, Abdel-Hameed et al.29 isolated
many fungi, including Cladosporium
cladosporioides from the atmosphere and have
evaluated production of mycotoxins by these fungi
using thin layer chromatography (TLC) and HPLC.
They found Cladosporium to be one of the
dominant genotypes in the air. Shelton et al.2 and
Lee et al.30 also recorded Cladosporiumat high
frequency inoutdoor air in several regions of the
US during all the seasons. Reason for sparse
occurrence of Cladosporium in Riyadh may be
high temperature and low relative humidity (RH)
conditions prevailing at the time of sample
collection.Comparatively lower concentration of
fungi including Cladosporium during summer was
recorded by Shelton et al.2 as well. Occurrence of
only two species in our samples points to low
genotypic diversity of Cladosporium in the area
of collection; in the other study29, cladosporioides
was the only species of Cladosporium recovered
from the air samples.
Since all the cultures were incubated
under identical water activity conditions and for
equal length of time, fungal genotype and
temperature were the only functional variables for
mycotoxin production. Considering absorbance to
be a function of mycotoxin concentration, it was
noted that C. cladosporioides cultures incubated
at lower temperatures of 10 and 15°C produced
more toxins (absorbance: 0.703 and 0.739
respectively) as compared to cultures grown at
higher temperatures of 20, 25, and 30°C
(absorbance: 0.049, 0.065, and 0.053 respectively).
Similarly, C. sphaerospermum cultures also
produced higher levels of mycotoxins at 10, 15,
and 20°C (absorbance: 0.659, 0.702, and 0.710
respectively) as compared to cultures grown at 25
and 30°C (absorbance: 0.061 and 0.090
respectively).
Production of mycotoxins in culture is
known to be influenced by water activity (aw) and
temperature 31, 32, 33. However, few studies have
investigated this aspect in Cladosporium. In the
case of Alternaria, level of alternuene (AE),
alternariol (AOH), and alternariol monomethyl ether
(AME) produced was markedly different at variable
incubation temperatures, the optimal being 25°C.
Gqaleni et al.34 studied the effect of temperature,
water activity and incubation period on production
of aflatoxin (AF) and cyclopiazonic acid (CPA) by
Aspergillus flavus and found that 30°C and 25°C
were the optimal temperatures for AF and CPA
respectively. Optimal temperature for production
of Fusarium mycotoxins was also recorded to be
25-30°C 35. It is interesting to note that optimal
temperature for production of mycotoxins in
Cladosporium is lower than reported for other
fungal genotypes. Association of temperature with
mycotoxin production acquires enhanced

J PURE APPL MICROBIO, 8(5), OCTOBER 2014.
4067ALWATBAN et al.: MYCOTOXIN PRODUCTION IN Cladosporium SP
relevance in the context of growing concerns of
climate change 36, 37.
HPLC procedures carried out without
standards have shown the presence of five
compounds in the extracts. Effect of incubation
temperature on production of mycotoxins is
apparent in HPLC analysis. Disappearance of the
fourth peak at lower temperature of 10 and 15°C in
C. cladosporioides and absence of the fifth peak
at higher temperature of 25 and 30°C in C.
sphaerospermum suggest that effect of
temperature on mycotoxin production may be
coupled with that of the genotype. Some previous
studies also reported such interaction31, 32, 33.
HPLC assays corroborate with the results
of spectrophotometry, indicating higher level of
mycotoxins at lower temperatures. Arranz et al.38
have emphasized suitability and authenticity of
HPLC procedures for identification of Fusarium
mycotoxins, which supports our choice of this
method for analyzing mycotoxins produced by
Cladosporium. However, Jing et al.39 have
cautioned that mycotoxins detected by HPLC need
to be verified by mass spectroscopy procedures.
They detected ochratoxinA supposedly produced
by contaminating fungi in longan fruit pulp with
HPLC procedures; but failed to verify it by electron
spray ionization-mass spectrometry (ESI-MS).
Sforza et al. 40 have convincingly
elaborated the advantages of using LC-MS and
GC-MS techniques for detecting mycotoxins at
very low concentrations. Plattner41 has used this
technique successfully for estimating production
of fumonisins and deoxynivalenol by Fusarium
graminearum, cultures. Analysis of our samples
by LC-MS has revealed much higher number of
molecules as compared to only three detected by
HPLC. This shows very high level of sensitivity of
this technique. Using LC-MS,Richard et al. 42 have
also reported precise detection of a large number
of mycotoxigenic molecules in mature corn silage.
However, unlike in our study, they have used
standards for several known mycotoxins of other
fungi and could link the production to their sources.
Several mycotoxins have been detected in food
items also with the help of this technique43.
GC-MS analysis in the present study has
revealed several molecules in the fungal extracts
of the two species of Cladosporium. Some of these
compounds seem to be at a very low concentration;
but were detected due to high sensitivity of the
GC-MS system. These findings point out that fungi
release a large number of molecules with diverse
activities, which may help them not only in growth
and survival but in protecting themselves and
modifying the biological activities of the host to
perpetuate their own life cycle. Using GC-MS,
Bloom et al.44 detected presence of several
mycotoxins in air with in fungus-infested buildings.
They have shown that GC-MS is a highly sensitive
technique and can detect molecules even at very
low concentrations. Edwards45 reported the
analysis of 300 samples of wheat grains and
detected a large number of known mycotoxins in
the samples. Similar to our study he has also
noticed presence of several molecules at very low
concentration. Abdel Hameed et al. 29 found
Cladosporium cladosporioides in air samples
collected from the industrial surroundings at a
frequency next only to Aspergillus species.
The present study provides an idea about
mycotoxigenic potential of airborne fungi and the
level of health risk they pose to the residents of a
given area. This study shows that prevalence as
well as genotypic diversity of Cladosporium is
low in the atmosphere of Riyadh city. Major
mycotoxins of Cladosporium (cladosporin,
isocladosporin, and emodin) were produced by
both species at all the incubation temperatures.
Our results also indicate that the level of total
toxins as well as the number of molecules produced
was higher at temperatures of 10-20°C as compared
to incubation at higher temperatures.
ACKNOWLEDGEMENTS
This study was supported by King Saud
University, Deanship of Scientific Research,
College of Science Research Center and King
Abdulaziz City for Science and Technology.
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