الفهرس 
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Abstract
Sixty eight bacilli (53 meso- & 15 thermo-philic) were isolated locally from different kinds of samples (soils, straw, bagasse or dung) collected from different districts in Dakahlyah & Damietta Governorates. Only 10 (mesophilic ones) were found to produce biodegradable biopolymer poly-3-hydroxybutyrate (PHB). They were belonging to genus Bacillus & six species; lentus, megaterium, mycoides, cereus, pumilus, and circulans. B. mycoides & megaterium were the best PHB producers in cultures. They synthesized PHB maximally in cells (~12 & 25 %, resp.) and also in whole culture at 24h. Byproducts molasses and starch were good carbon sources for PHB production by both cultures and could be used as cheap carbon & energy sources for production of PHB from bacilli. Sodium nitrate was the best inorganic nitrogen for PHB production by both, while peptone was the best organic nitrogen source for PHB cellular content & accumulation yield in culture of B. megaterium. Also, Corn steep liquor gave moderate yields. Best concentrations of carbon source (Molasses) & phosphate source (KH2PO4) were high (9%) & low (0.1%) levels; resp. Best aeration level was 250 rpm. Generally, basal/minimal medium was favorable for PHB production. Best environmental/physical conditions for PHB production by both were pH 6-7 & 7 and 34 & 37ºC, resp.