Abstract
When some bacteria grown in increasing concentrations of carbon, a polymer called Poly beta-hydroxyl butrate (PHB) was produced and accumulated inside the bacterial cell up to 70% of the cell dry weight. This material can be used safely in different modern application to replace plastic which has negative effects on man, animals and environments. This study aimed to isolate some actinomycetes for PHB degradation and optimization the growth conditions for maximum degradation. Contaminated soil samples were collected from industrial area of Jeddah and used for actinomycete isolations. The isolated bacteria were screened on medium containing PHB as a carbon source and presence of cleat zone on solid agar medium around the bacterial colonies mean PHB degradation. Out of thirty isolates, eight isolates were the most active in PHB degradation. After growth in liquid medium, these isolates were identified and characterized using morphological, physiological and chemical methods. Using molecular methods, they were belonging to different genera of actinobacteria. The most active isolate was Streptomyces sp. MM21.The effects of some growth factors on growth and PHB degradation was determined. Growth was measured by dry weight (g/l) while PHB degradation was detected by depolmerase assay (U/ml). It was clear that addition of 2.5 g/l of yeast extract and 1 g/l glucose enhanced both growth and PHB degradation. Similarly, adjusting medium at pH 7.0 and incubation temperature at 25 degrees C for 7 days lead to maximum PHB degradation. The maximum growth was in medium containing 0.5 g/l of PHB. In conclusion, PHB degradation was detected by actinobacteria and was affected by some physical and biochemical factors. It was noticed that optimization of growth conditions enhanced both growth and degradation process by the selected Streptomyces isolate.