Abstract
M.Tech. (Biotechnology)
With the rapid rise in untreatable diseases, researchers are compelled to search for new drugs that can combat these diseases. Plants are recognized as unlimited sources of bioactive compounds that can be used to treat different ailments and also be applied in various sectors including agriculture, pharmaceutical and food. In addition, plants are also known to be associated with endophytes such as bacteria and fungi, which are also regarded as fertile sources of bioactive constituents. Celtis africana is an ornamental and medicinal plant that is used to treat different ailments. In the study reported herein, the aims were to identify and characterize secondary metabolites produced by both the plant and its endophytes and to further investigate the antibacterial activity of C. africana extracts against fourteen pathogenic bacteria.
To achieve these aims, endophytes were isolated from fresh and apparently healthy aerial parts (leaves, stems and fruit) of C. africana. The isolated endophytes were then cultivated and secondary metabolites extracted sequentially with hexane, dichloromethane and ethyl acetate. Dried plant aerial parts were screened for the presence of phytochemicals, extracted successively with hexane, ethyl acetate and dichloromethane: methanol (1:1 v/v) and the crude extracts tested for antibacterial activity. The crude extracts of both the plant parts and endophytes were analyzed using two dimensional gas chromatography coupled with time of flight mass spectrometry(GC×GC-TOF/MS ) to determine their volatile secondary metabolites constituents.
From the results obtained, it is evident that C. africana has endophytic bacteria and fungi in the stem and fruit, but not in the leaves. Seven bacteria (Kocuria sp., Micrococcus luteus, Staphylococcus hominis, Bacillus sp., Staphylococcus saprophyticus, Brachybacterium conglomeratum and Arthrobacter sp) were isolated and identified. Four fungal endophytes, all belonging to the same genus (Aspergillus) were also isolated and identified, of which two were identified to genus level and two were found to be A. niger and A. flavus. The plant crude extracts showed antibacterial activity against seven of the test microorganisms, viz., Escherichia coli, Proteus mirabilis, Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae and Enterobacter aerogenes. These microorganisms are causal agents of various ailments ranging from food-borne illnesses to skin infections, urinary tract infections and pneumonia....