Antioxidant and antimicrobial activities of crude extracts of actinomycetes from soils

Abstract

A total of 17 actinomycetes isolated from soil collected from Nong Khai, Nakhon Ratchasima, Khon Kaen, Phichit, Chachoengsao and Udonthani Province, were evaluated on antimicrobial and antioxidant activities. They were identified as Streptomyces (16 strains) and Micromonospora (1 strain) based on their phenotypic and chemotaxonomic characteristics including 16S rRNA gene sequences analysis. Strain JA03 showed 98.95% similarity of 16S rRNA gene sequence to S. puniciscabiei DSM 41929T. Strain JA03 was found to be the novel species of genus Streptomyces based on whole genome average nucleotide identity (ANI). All these strains were evaluated on antimicrobial and antioxidant activities. Based on agar disk diffusion method, strain NE2-6 closely related to Streptomyces alboniger NRRL B 1832T, has the most potent antimicrobial activity against K.rhizophila ATCC 9341 and mild activity against S.aureus ATCC 25923. ET1-12 was effective on C. albicans ATCC 10231 and on K. rhizophila ATCC 934 and on B.subtilis ATCC 6633. ET2-2 closely related to Streptomyces diastaticus subsp. ardesiacus NRRL B 1773T exhibited moderate activity against B.subtilis ATCC 6633 and K. rhizophila ATCC 9341. CT2-4 closely related to Streptomyces capoamus JCM 4734T showed moderate effect on S.aureus ATCC 25923. Strain JA03 closely related to Streptomyces puniciscabiei DSM 41929T showed the highest phenolic content (33.4 µg GAE/ mg of extract) based on TPC assay and MKP33 closely related to Micromonospora yasonensis DS 3186T showed the highest FRAP value (135 µg AAE/ mg of extract) based on FRAP assay. Strain CT1-17 closely related to Streptomyces olivaceus NRRB L 3009T, showed potent scavenging activity (80.21±0.04%) at 1,000 µg/ml with IC50 value of 218.6±27.4 µg/ml based on DPPH assay. Strain MKP33 showed more potent in nitric oxide scavenging (49.3±1.96%) at 100 µg/ml than NE2-6 (49.6±1.34%) at 500 µg/ml. Cytotoxic effects of strains NE1-12, ET3-23, CT1-17, NE2-6, CT2-4, CT2-10, JA03 and MKP33 on RAW264.7 macrophage cells were evaluated by % cell viability. Strains NE1-12, CT1-17, JA03 and MKP33 showed no cytotoxic effect at 200µg/mL and strains CT2-4, CT2-10, ET3-23 and NE2-6 at 10 µg/ml on RAW 264.7 macrophage cells. Strain ET3-23 inhibited intracellular ROS generation (33±6.56%) in H2O2 (100µM) induced RAW 264.7 cells. CT2-10 at 10 µg/mL significantly inhibited NO production induced by LPS (100ng/ml) in RAW264.7 macrophage cells when compared with MKP33 at 200 µg/ml (13.87± 1.78µM and 2.9±1.02µM, respectively). In conclusion, these findings confirmed that Strain JA03 is the novel species of genus Streptomyces and possesses antioxidant activity. The actinomycetes isolated from soil provided the activity information in the development of good candidates for antibiotics and antioxidants.