الفهرس 
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Abstract
Cyanobacteria (Blue-green algae) are an ancient and diverse group of photosynthetic microogranisms which have evolved to inhabit many different and extreme environments. The incredible variety of niches inhabited by cyanobacteria indicates a high degree of biological adaptation which has enabled these organisms to thrive and compete effectively in nature. The bioactivity associated with cyanobacteria is indicative of chemical diversity which is an essential prerequisite in the modern drug discovery process. The recent work indicated that cynacobacteria are an exciting source of novel bioactive compounds, with a high number of the purified metabolites demonstrating activity.
In this study, Three species of blue green algae were isolated from fresh water in Beni-Suef city (Nostoc Commune, Oscillatoria granulate and Lyngbya purpurea. ) and they have exhibited antagonistic activity against Gram Positive, Gram negative bacteria and filamentous fungi.
Three experimental organisms have their own specific conditions for the production of the active anatibiotics.
The data indicated that:
(1) N. commune producd the antagonistic material maximally at 10days of incubation, where, O. granulate and L. purpurea produced its antagonistic material maximally at 14 and 16 days respectively during incubation
(2) Both the growth and antimicrobial activity were higher in shaken than in static cultures for N.c Commune, O. granulate and L. purpurea
(3) M18 medium was recorded to be the best medium for growth and antibiotic production by three species
(4) PH 8 was the best pH for growth and antibiotic production by three species
(5) Methanol was the best solvent for extraction of the antagonistic produced by N. commune.
The antimicrobial activities produced by the experimental organism (N. commune) were subjected to series of experiments aiming to identify its chemical composition. The antimicrobial activity was purified by using preparative TLC and silica gel column chromatography. The chromatographic studies of one gram total alcoholic extract of N. commune resulted in the isolation and purification of four compounds. The four compounds were long chain alc, sterol, triterpen and long chain fatty acid. The four compounds were tested for their biological activities against Bacillus subtillis, and showed that compound C was active with Bacillus subtillis while compounds A,B, D were not active against its.
In the present work we used UV spectra, NMR, IR and Mass spectra data to elucidete the chemical composition of the antimicrobial activities produced by N. commune but we need more chemical analyses to elucidate the complete structure of the obtained and purified compound from our isolates due to the very small amount obtained from these fractions in N. commune.