588 International Journal of Botany Studies ISSN: 2455-541X; Impact Factor: RJIF 5.12 Received: 18-01-2021; Accepted: 17-02-2021: Published: 23-02-2021 www.botanyjournals.com Volume 6; Issue 1; 2021; Page No. 588-597 Evaluation of antimicrobial, antioxidant and plant growth potential of endophytic bacteria isolated from leucas aspera and characterization of its bioactive metabolites Dayamrita K K 1 , Nivya Mariam Paul 2 Department of Microbiology, Mar Athanasius College, Kothamangalam, Kerala, India Abstract Exploration of bioactive compounds from plant endophytes increases the chance of finding novel compounds. Three endophytic bacteria having antimicrobial activity was isolated from the medicinal plant Leucas aspera. Due to superior antimicrobial activity, the strain isolated from roots of the plant was selected for further studies. It was characterized by morphological, cultural and biochemical studies. Scanning electron microscopic study supported the morphology of the cells. It has plant growth promoting attributes such as zinc solubilization, ammonia and organic acid production. Based on molecular and phylogenetic analyses, the strain presented 100% similarity to Enterobacter ludwigii strain Gol9. Bioactive compound was extracted from the isolate using a three solvent system and it showed zones of inhibition against both Gram negative and Gram positive bacteria. Thin layer chromatographic separation followed by FTIR and GC-MS analysis indicated a number of compounds. GC-MS analysis revealed six peaks of which the highest peak was shown by 1, 2-benzenedicarboxylic acid with a retention time of 40.761. The bioactive compound was found to possess anti-oxidant activities as well. These findings revealed that the endophytic bacterium isolated from Leucas aspera has the ability to produce potential bioactive compounds. Keywords: endophytes, bioactive compounds, Enterobacter ludwigii, gc-ms, ftir, antioxidant activity Introduction The medicinal plant Leucas aspera is commonly known as “thumba” or “thumbai”, belonging to the family Lamiaceae. It is an annual, branched, herb or undershrub erecting to a height of 15-60 cm with stout and hispid acutely quadrangular stem and branches. It possess various pharmacological activities like antifungal, antioxidant, antimicrobial, antinociceptive and cytotoxic activity. It is known to produce numerous phytochemicals such as triterpenoids, oleanolic acid, ursolic acid, b-sitosterol, nicotine, sterols, glucoside, diterpenes and phenolic compounds [1] . The use of medicinal plants is growing rapidly as demand for herbal drugs, natural health products and secondary metabolites are increasing. However, medicinal plants are threatened with extinction due to overharvesting and habitat destruction [2] . Medicinal plants produce bioactive compounds at very low levels and there is difficulty in extraction and purification of such compounds [3] . Endophytes are known to produce the same or similar bioactive compounds as their host [4] . De Bary introduced the term endophyte and defined it as any organism that grows within plant tissues. One or more endophytes can be present in a single plant and they can colonize various structures of a plant such as the stem, roots, leaves, petioles, seeds and buds. The population of endophytes in a plant is variable. It depends on various factors such as host species, host developmental stage, climatic conditions and inoculum density. Endophytes can be ‘obligate’ or ‘facultative’. Obligate endophytes are those that depend on the metabolism of plants for their survival, being spread by different types of vectors or by vertical transmission. Facultative endophytes are those that can survive outside the body of the host during a certain stage of their lifecycle. Endophytes can be bacteria (actinomycetes or mycoplasma) or fungi [5] . Endophytic bacteria are a class of specialized rhizobacteria that have the ability to invade plant roots after the establishment of a rhizospheric population [6] . Epiphytic bacteria from the phyllosphere can also enter the host plants via natural openings such as stomata and hydathodes or wounds and cracks created by wind, insects, and pathogen Attacks [7] . Endophytes are known to produce a wide array of bioactive metabolites which can be used as drugs for the treatment of various diseases [5] . Bioactive compounds produced by endophytes are much more advantageous than those that are produced by plants alone. Some of the bioactive compounds include antibiotics, alkaloids, phenols, terpenoids, nanoparticles, phytohormones, various enzymes, anticancerous compounds, antioxidants and antiviral compounds. The antimicrobial agents are effective against multi-drug resistant pathogenic microbes. Amines and amides can be used as insecticidal agents. They also confer disease resistance to the host plants. Endophytes also enhance plant growth via production of phytohormones such as IAA, ADCC, siderophore production and phosphate solubilization enhances water and nutrient uptake [8] . In continuing the search for new endophytes from medicinal plants as a source of bioactive compounds, we isolated for the first time an endophytic bacteria belonging to Enterobacter sp. from the root of Leucas aspera. The bioactive compounds produced by the endophyte were purified and identified by GC-MS analysis. Materials and Methods Collection of host plant and surface sterilization Healthy leaves, flowers and roots of Leucas aspera, were randomly collected from natural populations of Kothamangalam (10°03'27.2"N 76°36'57.4"E), Kerala, India and kept in sterilized polythene bags and brought to the