Objectives: It was intended to isolate endophytic bacteria from Plectranthus amboinicus leaves to elucidate the plant growth promotion potential.
Methodology: Phytochemical constituents of Plectranthus amboinicus leaves were analyzed following standard procedures. Endophytic bacteria were isolated in nitrogen limited medium after surface sterilization process as described by Coombs & Franco (2003) and identified by biochemical, molecular analyses. Plant growth promotion and quorum quenching potential of the isolate was determined as described by Patel et al. (2011). Probiotic potential of the isolates was elucidated following a series of assays (Ahire et al. 2011).
Results: Phytochemical investigation of the leaves revealed the presence of alkaloids, flavonoids and terpenoids. An endophytic bacterium with probiotic properties was isolated and identified as Rhodococcus globerulus. Plant growth promotion (PGP) traits such as phosphate solubilization, IAA production and ACC deaminase activity of R. globerulus was estimated to be 37.3 μg ml-1, 36.7 μg ml-1 and 35.00 ± 1.2 nmol α-ketobutyrate mg-1 h-1 respectively at 60 h of incubation. The isolate was found to produce trihydroxamate siderophores with hexadentate ligands. Presence of the bacterium within the leaf tissues was confirmed by SEM imaging. R. globerulus was found to produce quorum sensing inhibitor (QSI) molecules. Endophytic isolate was also found to possess probiotic potential.
Conclusion: The results illustrate that the plant-associated microbiome serve as a repertoire of metabolic products that facilitate nutritional and defense pathway of the host plant. Probiotic properties of the endophyte confer an added advantage to the therapeutic potential of the plant P. amboinicus.
Plant growth promotion;Plectranthus amboinicus;probiotic;quorum sensing;Rhodococcus globerulus;siderophores