الفهرس 
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Abstract
Microbial endophytes are group of microorganisms that colonize the inter- and/or intracellular locations of plants. In this study, Acacia nilotica and citrullus colocynthis were the chosen medicinal plants (based on their history of use in ethnopharmacology) as candidates for the isolation of bacterial endophytes. Bacterial endophytes were isolated from their seeds after proper surface sterilization and identified by 16SrDNA sequence analysis. Erwinia rhapontici is the bacterial endophyte of Acacia nilotica, while Acinetobacter calcoaceticus is the bacterial endophyte of Citrullus colocynthis. secondary metabolites were isolated from the culture filtrates of fermentation broth (tryptone soy broth) and extracted by three solvents (n-hexane, ethyl acetate, and n-butanol) for each of isolated endophyte. Additionally, two pure compounds, m- and p-anisaldehydes, were also isolated from the culture filtrate of Erwinia rhapontici, and their structures were established using NMR spectroscopy. Using GC-MS, the chemical composition of secreted secondary metabolites in their culture filtrates was determined. Using the SRB (Sulforhodamine B) assay, the cytotoxic effect of crude extracts and purified compounds was evaluated against human cancer cell lines DU-145, HepG2, and MCF-7.
The most effective crude extracts were the acetyl acetate fractions from the culture filtrate of both endophytic bacteria. The inhibitory concentration (IC50) for acetyl acetate fractions of tested cell lines were 52.36μg/mL, 84.45μg/mL and 62.27μg/mL and 58.18 μg/mL, 77.51 μg/mL, and 59.39 μg/mL for E. rhapontici& A. calcoaceticus respectively. m-anisaldehyde that was isolated from Erwinia rhapontici culture filtrate recorded a good inhibitory effect on tested cell lines specially for MCF-7 cancer cells with IC50 value of 89.04 μg/mL for DU-145, HepG2, and MCF-7, respectively. P-anisaldehyde exhibited mild cytotoxic effect specially MCF-7 cells. n-Hexan crude extract of A. calcoaceticus also exhibited cytotoxic effect against tested cancer cell lines specially that of prostate cancer with IC50 value of 89.04 μg/mL. Non effective fractions with IC50>300 μg/mL were n-Hexan and n-butanol crude extracts for Erwinia rhapontici and so the butanol crude extract of A. calcoaceticus. It is evident that both E. rhapontici and A. calcoaceticus could be utilised as renewable bioresources for the manufacture of anticancer drugs.