Antibacterial Activity of Endophytic Bacillus safensis Isolated from Ophioglossum reticulatum L.

Aims: This study is aimed to explore the potential of endophytic bacterial population of Ophioglossum reticulatum L., a pharmacologically important perennial fern, for production of antimicrobial compounds.

Place and Duration of Study: The study was conducted in the Microbiology Laboratory, Department of Botany, University of Calcutta, Kolkata, India, between March 2016 and August 2016.

Methodology: Phenotypically distinct bacterial endophytes were isolated from surface sterilized segments of O. reticulatum L. and screened for the production of antimicrobial metabolites following cross-streak and agar-cup assay methods. The most potent antibacterial isolate was characterized in terms of morphological, physio-biochemical features, and 16S rDNA sequence analysis. The antibacterial antibiotic produced in tryptic soy broth was isolated from the fermented medium in ethyl acetate and partially purified by preparative TLC. The nature and antimicrobial spectrum of the antibiotic was determined following standard biochemical and microbiological methods.

Results: The potent endophytic bacterial isolate OPL 19 was identified as Bacillus safensis (GenBank accession number KY029081) following a polyphasic approach. The antibacterial compound produced by Bacillus OPL 19 was found to be relatively thermostable, non-polar, and lipoidal in nature showing distinct absorption peaks at 220 and 235 nm. In addition it showed broad spectrum of activity inhibiting wide variety of Gram-positive and Gram-negative bacteria including Acinetobacter baumannii, Bacillus subtilis, Cellulosimicrobium cellulans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus etc.

Conclusion: This study not only indicated the endomicrobiota as a potential resource for novel antimicrobials but also highlighted the fact that the therapeutic properties of O. reticulatum L. could be correlated with its endophytic association.