Isolation of Actinomycetes from Soil Rhizosphere of Peperomia pellucida L. from Karst Maros Ecosystem as Antimicrobial Compound Producer

Infectious diseases pose a significant global challenge, and one approach to treatment is through antibiotic production. Various methods exist for obtaining antibiotics, one of which involves isolating Actinomycetes, known for their potential as producers of antimicrobial compounds. This research investigated antimicrobial agents produced by Actinomycetes isolated from the rhizosphere soil of Peperomia pellucida L. in the Karst ecosystem of Maros, South Sulawesi. Actinomycetes were isolated from the soil surrounding P. pellucida plants, resulting in 22 pure isolates, which were then screened for antimicrobial activity against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Candida albicans ATCC 10231 using antagonistic assays. Screening results revealed two Actinomycetes isolates, coded as RKS-0.3- 13 and RKS-0.4-04, exhibiting the greatest antimicrobial activity. These isolates underwent further processing through fermentation for secondary metabolite production using M1 media under agitation conditions for 16 days at 150 rpm. The fermentation products were then sonicated and separated into supernatant and biomass. The supernatant was extracted using ethyl acetate (1:1 v/v), and the resulting ethyl acetate extract was tested for antimicrobial activity using paper disks. Test results indicated that the ethyl acetate extract inhibited the growth of E. coli ATCC 25922, S. aureus ATCC 25923, and C. albicans ATCC 10231 at a concentration of 0.5 mg/20 μL. Chemical compound profiles of ethyl acetate extracts from P. pellucida plants in karst and non-karst ecosystems, as well as secondary metabolite extracts from both Actinomycetes isolates, exhibit differences in RF values in chromatographic spots on Thin Layer Chromatography plates. Molecular identification of the Actinomycetes isolates based on the 16S rRNA gene sequence reveals that RKS-0.3- 13 is closely related to Streptomyces chartreusis CP108840.1 with a similarity value of 99.86%, and RKS-0.4-04 is closely related to Streptomyces neopeptinius KU324439.1 with a similarity value of 99.93%.