Antimicrobial and Antioxidant Compounds in Endophyte Isolate L-003 Obtained from the Aquatic Plant Nelumbo nucifera

Background: Microorganisms from understudied habitats have been shown to be an important source of novel bioactive compounds. Endophytes constitute an underexplored group of microorganisms, of which those from aquatic plants have been even less studied. Nelumbo nucifera (lotus) is an aquatic plant with medicinal properties. A screening program for endophytes from N. nucifera by our research group resulted in many microbial isolates, of which isolate L-003 was a promising candidate, exhibiting antimicrobial and antioxidant activities. Objectives: The major objectives were to characterize the endophyte L-003 for its antimicrobial and antioxidant properties, identify the constituent bioactive compounds by GC-MS and characterize their activities further using in silico software. Methods: L-003 was identified by PIBWin software. Antimicrobial activity of the aqueous and organic extracts of culture supernatant of L-003 was checked against a panel of bacteria and fungi. Since the ethyl acetate extract showed the best antimicrobial activity, it was further characterized by thin layer chromatography, an activity confirmed by bioautography and purified by column chromatography. Total antioxidant capacity was assayed by standard techniques. Partially purified metabolite fingerprints were identified by GC-MS analysis. Results: Based on morphological and biochemical analyses, isolate L-003 was identified as belonging to Streptococcus sp. All the organic solvent extracts showed antimicrobial activity. Ethyl acetate extract showed maximum antimicrobial activity against all selected targets and exhibited antioxidant activity too, though butanol and aqueous extracts showed higher antioxidant activity. Two compounds, Acetic acid,-hydroxy, methyl ester and Disulfide, dipropyl, were identified by GC-MS in the metabolite fingerprint. These compounds showed differences in observed and calculated retention indices and could, therefore, be novel. In silico activity, characterization confirmed the antimicrobial and antioxidant properties attributed to these compounds. Conclusion: This is the first study reporting metabolite fingerprinting, identification and characterization of bioactive compounds from an endophytic isolate of Nelumbo nucifera. We conclude that endophytes from aquatic plants could be prospective sources of bioactive compounds, in this case with antimicrobial and antioxidant activities.