In Vitro Antimicrobial Activity Screening of Bacteria Endophytic to Ethnomedicinal Plant Rauvolfia serpentina (L.) Benth. ex. Kurz

Abstract

Introduction: Microbial endophytes colonizing internal tissues of living plants provide benefits to their host by promoting plant growth and protection against microbial infectious through the production of wide ranges of metabolites. Members of such endophytic community harbouring medicinally important plants are known to synthesize several antimicrobial compounds. The present study aims to explore bacterial endophytes of ethnomedicinal plant Rauvolfia serpentina (Apocynaceae) for producing novel antimicrobial metabolites of pharmaceutical and biotechnological importance. Materials and Methods: The culturable bacterial endophytic diversity of R. serpentina (L.) Benth. ex. Kurz. has been screened for producing antimicrobial compounds following cross-streak and agar well diffusion assay methods against several test microbial strains. The bioactive compound was isolated and partially purified from the cell-free culture filtrate following chromatographic methods. Results: The endophytes revealed low colonization frequency and isolation rates in the root and stem respectively. In vitro antimicrobial screening of 12 phenotypically distinguishable endophytes resulted in the selection of a potent antimicrobial isolate RAU 305 identified as Pseudomonas aeruginosa RAU 305 (Genbank accession number KR816098). Cell-free culture filtrate of RAU 305 showed broad spectrum of antimicrobial activity by inhibiting Paenibacillus, Micrococcus, Arthrobacter, Rhodobacter, Mycobacterium, Bacillus, Escherichia, Staphylococcus, Klebsiella, Aspergillus, Colletotrichum and Pythium. The antimicrobially active component extracted in butanol and chloroform was partially purified by column chromatography followed by a preparative thin layer chromatography and the homogeneity of the compound was confirmed using different solvent systems. Conclusions: More detailed characterization and identification of the active component is essential to explore the metabolic potential of this endophytic bacterium in future.