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Poly β- hydroxyl butrate (PHB) is a polymer produced by bacteria and can be used safely in different modern application to replace biobased plastic which has adverse effects on the environments. This study is aimed to isolate some fungi for PHB degradation and optimise the growth conditions for maximum degradation. Contaminated soil samples were collected from the industrial area of Jeddah and used for fungal isolations. All fungal isolates were screened for PHB biodegradation on solid agar medium. Out of 20 isolates, 2 isolates were the most active in PHB degradation. They were identified as Trichoderma asperellum NM 6, and Aspergillus fumigates NM10 using morphological and molecular methods. The effects of some growth factors on growth and PHB degradation by the two isolated fungi were determined. Growth was measured by either CPV (ml) or dry weight (g/l) while PHB degradation was detected by depolymerase assay (U/ml). Presence of yeast extract (2.5 g/l) and glucose (1 g/l) enhanced both growth and PHB degradation by the two isolates. Similarly, adjusting medium pH at 7-7.5 and incubation at 25°C after for five days led to maximum growth and PHB degradation. The presence of PHB in growth medium enhanced both growth and PHB degradation and the maximum growth (CPV ml or dry weight (g/l) were in medium containing 0.5 g/l of PHB for both tested fungi. The maximum growth, measured by either CPV (ml) or dry weight (g/l), was in the medium that was inoculated with 10x106 spore/ml for the two tested fungi. In conclusion, PHB degradation by the two tested fungi was similar. It was affected by the same physical and biochemical factors and optimisation of these conditions enhanced both growth and degradation process by the two tested fungi.
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