Bioactivities of secondary metabolites of two actinomycetes Streptomyces parvulus GloL3, and Streptomyces lienomycini SK5, endophytes of two Indian medicinal herbs- Globba marantina L. and Selaginella kraussiana (Kunze) A. Braun.

Abstract

Endophytic actinomycetes are potential sources of novel pharmaceutically active metabolites, significantly advancing natural product research. In the present investigation, secondary metabolites from two endophytic actinomycetes, Streptomyces parvulus GloL3, and Streptomyces lienomycini SK5, isolated from medicinal plant taxa, Globba marantina, and Selaginella kraussiana, exhibited broad-spectrum bioactivity. Ethyl Acetate (EA) extract of SK5 showed antimicrobial activity against nine human pathogens, including Methicillin-resistant Staphylococcus aureus (MRSA), Candida tropicalis, and C. albicans, with a minimum microbicidal concentration (MMC) of 50-300 µg mL^-1. It healed the MRSA-mediated wounds in Swiss albino mice in vivo. EA extracts dissociate the pathogenic cell membranes and cause leakage of biomacromolecules-nucleic acid, protein, and potassium ions. Also, critical housekeeping enzymes involved in the cellular respiratory mechanisms of the pathogens were blocked. GloL3 has antioxidative potentialities against DPPH, ABTS, FRAP, and H₂O₂ free radical generators with an IC₅₀ value of 21.18 ± 0.33, 43.58 ± 0.91, 88.24 ± 1.24, and 111.03 ± 6.42 µg mL^-1. It improves the enzymatic antioxidant parameters in treated peritoneal macrophage cells of Swiss albino mice. Constituents of the EA extracts of GloL3 and SK5 are bactobolin, actinobolin, 5-(2-aminoethyl)-1 H imidazole-2-carbaldehyde, isovaleric acid, fulvic acid, phenol, 4-[2-(methylamino) ethyl]-, eicosanoic acid, heptadecanoic acid, etc. The present findings suggest that metabolites from the endophytes of medicinal plants hold potent pharmaceutical utilities.