Isolation of Actinomycetes from rhizosphere soil of Nephrolepis cordifolia as a producer of antifungal compounds in the karst of Bantimurung

Actinomycetes are anaerobic bacteria, either rod-shaped or filamentous, Gram-positi0ve, that produce antibiotic and antifungal compounds. This study aims to isolate and explore the potential of actinomycetes as producers of antifungal compounds from the rhizosphere of Nephrolepis cordifolia in the karst ecosystem of Bantimurung, South Sulawesi, Indonesia. Primary and secondary screenings were conducted against Candida albicans and Aspergillus niger using 17 Actinomycetes isolates from the rhizosphere of Nephrolepis cordifolia. All isolates were tested antagonistically, and two isolates that exhibited the highest antifungal activity were designated RKP-A.1-2 and RKP-B.1-1. These active isolates were then fermented for 16 days at a speed of 150 rpm. The fermentation products were then sonicated to separate the supernatant and biomass. The supernatant was extracted using ethyl acetate (1:1 v/v) and tested using the diffusion method. The test results indicated that the ethyl acetate extract from the fermentation of both isolates was able to inhibit the growth of Candida albicans up to a concentration of 0.5 mg/μ of extract from RKP-A.1-2 and RKP-B.1-1. The compound profiles of the secondary metabolites produced by Actinomycetes and extracts from karst and non-karst Nephrolepis cordifolia showed different compound profiles, as evidenced by distinct Rf values. Phylogenetic analysis of the 16S rRNA gene sequences revealed that RKP-A.1-2 and RKP-B.1-1 are closely related to Streptomyces sp . with a similarity value of 100.00%. From the results of this study, it can be concluded that Actinomycetes from the rhizosphere of Nephrolepis cordifolia in the karst ecosystem of Bantimurung have potential as producers of antifungal compounds that warrant further investigation. This research provides a significant contribution to the understanding and utilization of these microorganisms as potential sources of bioactive compounds.