Isolation of Bacillus amyloliquefaciens M13-RW0 from Soil and Evaluation of its Antifungal Activity.

Background: The frequency of observed invasive Aspergillosis has increased in recent years. Infection with other molds happens but does not lead to a large proportion of invasive infections. The present study aims to isolate Bacillus amyloliquefaciens M13-RW0 from soil and evaluate its antifungal effects against some saprophytic fungi, such as Aspergillus niger, Aspergillus flavus, and Mucor hiemalis.

Materials and methods: In this research, a total of 150 samples (from the soil, air, and surfaces) were prepared from different parts of Isfahan, Iran. Isolation and purification of growing bacteria were conducted using the nutrient agar medium. The inhibitory effects of 100 isolated bacteria were evaluated against the growth of A. niger, A. flavus, and M. hiemalis, 4 bacteria were isolated with inhibitory effects against the selected fungi, and consequently, one of the bacteria isolated from the soil samples was found to show the highest inhibition of fungal growth. Quantitative evaluation of the growth inhibitory effect was performed using linear culturing of fungal suspension (10⁴ spore/ml) at distances of 5, 10, 15, 20, 25, and 30mm from bacterial isolate (0.5 McFarland) on Sabouraud Dextrose Agar (SDA) medium. Results were checked 24, 48, 72, and 96 hours later. The bacterial isolate with the most inhibitory effect was identified by phenotypic and molecular tests.

Results: According to the results, among the 4 inhibitory bacterial isolates, Bacillus amyloliquefaciens strain M13-RW01, isolated from the soil samples, was identified as the bacterium with the most significant potential antifungal activity. The strong inhibitory effect was revealed after 48 hours for all distances of 15mm and more between the fungi and the bacterium.

Conclusion: The identified bacterium could not only be considered an inhibitor bacterium against saprophytic fungi but could also be put forward to help produce new antifungal drugs for controlling fungal diseases.