Effect of Some Ecological Factors on Thegrowth of Aspergillus niger and Cladosporium sphaerospermum

Indoor airborne fungi have been implicated in human health problems, damage to building materials, books, clothes and stored foods, which effected by different ecological factors. Aspergillus niger and Cladosporium sphaerospermum are the most dominant indoor airborne fungi were obtained from our previous study. The effect of normal indoor conditions (Temperature and Relative Humidity) on their growth was studied. Including their nutrients growth requirements. The PDA medium was the appropriate growth medium for Cl. sphaerospermum, with a significant difference at (p<0.05); where as GYA medium was the appropriate growth medium for A. niger, with no significant difference. The temperatures 25 and 30°C favored colony diameter growth for Cl. sphaerospermum and A. niger, respectively with a significant difference at (p<0.05). The growth of Cl. sphaerospermum increased to reach its maximum at 100% RH. Whereas, A. niger prefers to grow at lower RH comparing to Cl. sphaerospermum to reach its maximum at 75% RH with a significant difference at (p<0.05). Controlling the normal indoor conditions can play a significant role in reducing the growth of indoor airborne fungi. Cl. sphaerospermum can be used as indicator fungi for the high humidity level in residences. The result has proved that keeping the humidity low enough can prevent fungi growth.

Most people in developed countries spend more than 90% of their time indoors, in locations such as homes, offices and factories (Brasche and Bischof, 2005;Li and Kendrick, 1995). Concern regarding the health effects of indoor air quality has grown. In Saudi Arabia that has along, hot summer, the significance of indoor air quality is obvious.
Environmental factors such as humidity and temperature plays an important role in dispersing fungi spores in air for short and long distances and when spores deposited a solid or liquid surface and if conditions of moisture and food are appropriate, they germinate (Bennett, 2010;Goncalves et al., 2010). Normal indoor conditions such as humidity and temperature provide a suitable environment for the growth of a wide of fungal spores (Ababutain, 2011;Li and Kendrick, 1995).
Few researchers on airborne fungi reported that an increase in fungi spore concentration was seen at air temperatures between 15 and 25°C and relative humidity at 60-70% (Segvic and Pepeljnjak, 2006). Relative humidity and temperature extremities may result in decreased airborne fungi spore concentration (Levetin and Horowitz, 1978). Aspergillus, Penicillium and Cladosporium were Science Publications AJAS considered to be closely related to local microenvironments and urbanization (Awad, 2005).
In order to understand the significance of indoor airborne fungi and to be able to predict the occurrence of indoor airborne fungi, it is critical to indicate the relationships of indoor airborne fungi concentration to normal indoor conditions. Thus, the influence of three culture media, temperature and relative humidity on the growth of most dominant indoor airborne fungi A. niger and Cl. sphaerospermum were studied.

Environmental Studies
The effect of some cultural conditions such as nutrient media, incubation temperature and Relative Humidity (RH) on the linear growth of two dominant indoor fungi (Aspergillus niger and Cladosporium sphaerospermum), was carried out. The inoculums were in the form of disks, prepared using a sterile cork poorer (5 mm). The disks were obtained from homogenous growth of 5 days old cultures grown in Potato Dextrose Agar (PDA) medium at 28°C. All experiments were performed in triplicate.

Effect of Different Culture Media
The tested fungi were cultivated on three different media of: (PDA), Glucose Yeast extract Agar (GYA) and Czapek's agar (Cz). Petri Plates were prepared with the different media and inoculated with the tests fungi. Petri Plates were incubated in darkness at 28°C for one week. After the end of incubation period, the linear growth (cm) was determined.

Effect of Temperature
The tested fungi Cl. sphaerospermum and A. niger were incubated in PDA and GYA media respectively and incubated in darkness at 5, 10, 15, 20, 25, 30, 35, 40 and 45°C for one week. After the end of incubation period, the linear growth (cm) was determined.

Effect of Relative Humidity
Seven levels of RH were maintained by mixtures of appropriate combinations of concentrated sulphoric acid and distilled water (Table 1) as described by Ayyasamy and Baskaran (2005). Mixtures were taken in the desiccators for each level of RH.

Statistical Analysis
Data were analyzed using SPSS Version 15.0 (SPSS. Inc., Standard Version).

Effect of Different Culture Media
The PDA medium was the appropriate growth medium for Cl. sphaerospermum with a significant difference at (p<0.05); where as GYA medium was the appropriate growth medium for A. niger, with no significant difference ( Fig. 1 and Table 2). The colony diameter was 5.33±0.3 cm and 2.7±0.15 cm for A. niger and Cl. sphaerospermum respectively.

Effect of Temperature
The growth of A. niger and Cl. sphaerospermum on different temperatures is shown in Fig. 2 and Table 3. The temperatures 25 and 30°C favored colony diameter growth for Cl. sphaerospermum and A. niger, respectively so they considered as the optimum growth temperature. The temperatures range for Cl. sphaerospermum was narrow from 15-30°C whereas the temperature range for A. niger was wide from 10-40°C. At the temperature of 10°C, A. niger was unable to form spores and only the mycelium growth has appeared.

Effect of Relative Humidity
The growth of A. niger and Cl. sphaerospermum on different RH is shown in Fig. 3 and Table 4.

DISCUSSION
The present study revealed that the PDA medium is a general medium for growth due to its nutritional value, which is in agreement with (Trindade, 1994). A similar result was obtained by (Palacios-Cabrera et al., 2005) they found that the A. niger was able to grow in all culture media, Czapeck Yeast extract Agar (GYA), Dichloran 18% Glycerol Agar and Malt Yeast extract 40% Glucose Agar (MY40G).
The result showed that temperature was clearly the most important growth factor. Upon the present results, Cl. sphaerospermum considered as Mesophiles whereas A. niger considered as Thermophiles. Many researchers support our results; Subbarao et al. (1993); Alwakeel (2008) and Nawar (2008) found that the optimum growth temperature for the A. niger was 30°C. Present result do not support the statement of Palacios-Cabrera et al. (2005) who showed that A. niger prefers to grow at temperatures higher than 30°C. In addition, Al-Garni et al. (2007) found that 25°C was the optimum linear growth for A. niger. Pitt and Hocking (1997) found the temperature of 8°C was inhibitory for A. niger. In addition, Al-Garni et al. (2007) were found that A. niger failed to grow at 10°C and 55°C. Whereas, Nawar (2008) found that A. niger was unable to grow at temperature of 15°C which differs from the result obtained in the present study.
Results of the present study partly agree with the report of Tasic and Miladinovic-Tasic (2007) they noticed that great number of Cladosporium spp., does not grow at the temperature above 35°C and does not multiply at the temperature 25°C.
The present study clarified that the two fungi were able to grow at a wide rang of RH. In general, the growth of Cl. sphaerospermum increased to reach its maximum at 100% RH, thus Cl. sphaerospermum can be used as indicator fungi for the high humidity level in residences. On the other hand, A. niger prefers to grow at lower RH to reach its maximum at 75% RH compared to Cl. sphaerospermum. Growth of A. niger and Cl. sphaerospermum decreased by low RH up to 65 and 75%, respectively. In addition, Al-Garni et al. (2007) and Nawar (2008) found that the growth of A. niger increased regularly with increasing RH up to 100%. The result has proved that keeping the humidity low enough can prevent fungi growth. The present results support the findings of the Ryan (2002) and Ren et al. (2001) who both found that there is a significant association between dampness and airborne fungi concentration, confirming that houses experiencing dampness have a greater concentration of airborne fungi than dry houses.
Overall, the differences in the optimum growth temperature and RH level may be attributed to the difference in strains isolated from different regions around the world. My previous study (Ababutain, 2011) revealed that the temperature and RH level were more effective factors than most weather condition. The results of the present study confirmed this finding.

CONCLUSION
The importance of studying ecological factors appears through their direct impact on the airborne fungi concentration. Therefore, by controlling these factors airborne fungi concentration will decrease.