Unveiling Actinobacteria Potency from The Sungai Wain Protected Forest, East Kalimantan, Indonesia: A Promising Source of Antibacterial, Anti-Biofilm, and Antioxidant Compounds
Abstract
Actinobacteria are Gram-positive bacteria widely distributed in soil environments and are well known for producing diverse bioactive compounds. Almost 80 % of the antibiotics in the world are derived from actinobacteria. However, inappropriate use of antibiotics has accelerated antibiotic resistance in many pathogenic bacteria. This study aimed to screen and analyse actinobacteria from the soil of the Sungai Wain protected forest to determine their antimicrobial, antibiofilm, and antioxidant potential. The research involved several stages, including preliminary screening; secondary metabolite production; determination of Minimum Inhibition Concentration (MIC), Minimum Bactericidal Concentration (MBC), anti-biofilm assay, and antioxidant assay; 16S rRNA gene identification; biosynthetic genes detection (PKS and NRPS); and compound profiling using GC-MS. Three isolates, K22S-22, 31, and 36 exhibited the highest inhibition zones, with K22S-22 showing the strongest activity against Staphylococcus aureus and Bacillus subtilis (IC50 = 1.033±0.033 μg mL-1 and 4.155±0.028 μg mL-1, respectively). Strain K22S-22 also displayed antioxidant activity (DPPH IC₅₀ = 67.59 ± 0.020 μg mL⁻¹) and significant antibiofilm effects (inhibition IC₅₀ = 4.541 ± 0.124 μg mL⁻¹; eradication EC₅₀ = 50.71 ± 0.029 μg mL⁻¹). Molecular identification revealed K22S-22 as Streptomyces rapamycinicus NRRL B-5491 (T) with a similarity value of 99.08 %, harbouring PKS-I, PKS-II, and NRPS genes. The Gas Chromatography-Mass Spectroscopy analysis (GC-MS) shows that Hexadecanoic acid is the dominant compound based on its area percentage. These findings highlight Streptomyces K22S-22 is a promising source of metabolites that exhibit potent antimicrobial, antioxidant, and antibiofilm characteristics, presenting opportunities for new therapeutic uses against multidrug-resistant (MDR) pathogens.
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