Identification and Antibacterial Activity of Actinomycetes Isolated From Medicinal Plant Andrographis paniculata Rhizosphere Soil

Research related to the characterization of the secondary metabolites of actinomycetes rhizosphere medicinal plants, as well as the molecular identification of actinomycetes as an antibacterial compound producer was carried out on actinomycete isolates obtained from the rhizosphere soil of medicinal plants in South Sulawesi. The purpose of this study was to isolate actinomycetes from Andrographis paniculata rhizosphere and to determine their antibacterial activity against Escherichia coli and Staphylococcus aureus. Finally, actinomycetes that produce antibacterial compounds were identified as well.

Two isolates of actinomycetes were obtained from A. paniculata named SM-4 and SM-6, which were fermented in the starch nitrate broth (SNB) medium for 14 days. The supernatant and biomass of the fermentation yield were separated, and then the supernatant was extracted using ethyl acetate. Next, the antibacterial activity test was conducted by the diffusion method using a paperdisk. Eventually, the identification of actinomycetes SM-4 and SM-6 was based on the sequence analysis of the 16S rRNA gene using universal primers 27f and 1492r.

The antibacterial activity of ethyl acetate extracts could inhibit the bacteria test to 2 mg concentration. Based on phylogenetic trees, actinomycetes SM-4 and actinomycetes SM-6 had the highest similarity with Streptomyces griseorubiginosus and Streptomyces phaeopurpureus, as well as Streptomyces purfeofuscus and Kitasatospora azatica, respectively.

In general, actinomycetes SM-4 isolated from rhizosphere A. paniculata had the highest similarity with Streptomyces griseorubiginosus and Streptomyces phaeopurpureus with a similarity level of 97%. In addition, SM 6 isolated from the rhizosphere of A.s paniculata demonstrated the highest similarity with Streptomyces purfeofuscus and K. azatica with similarity levels of 97%. Finally, the thin layer chromatography-bioautography test revealed that the ethyl acetate extract from actinomycetes SM-4 had antibacterial activity at Rf 0.14 and 0.4 and was assumed to be a class of terpenoid compounds