Abstract
Medicinal plants are important source of compounds which are useful in the treatment of various diseases. The rich and diverse compounds in medicinal plants play a significant which can contribute in the commercial production of drugs. The demand on medicinal plants is increasing in both developing and developed countries for contribution in the discovery of pharmaceutically active substances; and these plant species are threatened with extinction from overharvesting, habitat destruction. The bacterial endophytes residing in plant tissues of medicinal plants are regarded as an alternative approach to produce plant-related biologically active compounds since they have a symbiotic relationship with the host plant and possess the same medicinal properties as their plant host. Present study was aimed to investigate the antimicrobial activity of secondary metabolites produced by bacterial endophytes from Dicoma anomala. Dicoma anomala is considered a valuable medicinal plant known for antimicrobial, anti-inflammatory, antioxidant, antiplasmodial, and anticancer properties. Eleven bacterial endophytes were isolated from the plant tissues (leaves and roots) of D. anomala and identified using 16S rDNA, which were classified into five genera specifically Bacillus, Staphylococcus, Stenotrophomonas, Enterobacter and Pantoea, with Bacillus as a dominant genus with five isolates; Staphylococcus with two isolates and Stenotrophomonas with two isolates and Pantoea with one isolate. Selected bacterial endophytes were evaluated for their plant growth promoting activities and were found to produce ammonia, nitrogen, Aminocyclopropane-1- carboxylase (ACC) deaminase. The crude extracts of the plant (leaves and roots) as well as selected bacterial endophyte’s crude extracts were evaluated for antimicrobial activity against five pathogenic strains Escherichia coli (ATCC 25922), Bacillus cereus (ATCC 10876), Staphylococcus aureus (NCTC 6571), Pseudomonas aeruginosa (ATCC 27853) and Klebsiella Oxytoca (ATCC 13182); and displayed inhibition concentrations ranging from 0.312 mg/ml to 10 mg/ml. Conclusively the plant and its bacterial endophytes were able to produce numerous phytochemicals such as steroids, saponins, flavonoids, tannins and terpenoids. Furthermore, using gas chromatography-high resolution time-of-flight mass spectrometer (GC-HRT) to identify volatile bioactive secondary metabolites; results from this study revealed that D. anomala plant extracts and its bacterial endophytes have volatile bioactive secondary metabolites with reported biological activities such as antimicrobial, anti-inflammatory, antioxidant, anti-neoplastic, antiseptic, anti-cancerous, and antifungal properties. In addition, ii whole genome of one novel bacterial endophyte named Bacillus sp. strain MHSD28, was sequenced ,assembled, annotated and phylogenomically classified as a potential new species; the data obtained assisted in identifying genes important for bacterial endophyte lifestyle and will also improve data analysis in genomics for studies associated with Bacillus species adopting an endophytic lifestyle. Based on literature review and results obtained from this study, it is concluded that bacterial endophytes isolated from D. anomala as can be a new source for compounds in production of drugs; to the best of our knowledge this is the first report on bacterial endophytes associated with D. anomala.
M.Sc. (Biotechnology)