Production of poly-β-hydroxybutyrate (PHB) by Azospirillum and Rhizobium sp

Abstract

T HIRTY five bacterial isolates of Azotobacter were isolated from different sources, nine samples from clay soil and six samples from irrigation water which collected from different localities in El-Gharebia Governorate (Basyion) and Kafr El-Sheikh Governorate (Sakha) to study their ability for accumulation of biodegradable biopolymer poly-β-hydroxybutyrate (PHB) by screening for presence / absence of PHB using a Nile-red staining approach. Also, to achieve enough biomass from the efficient isolates for the production of PHB various incubation times, different fermentation media, pH, temperature, carbon and nitrogen sources were used. Among all isolates, the amount of PHB in the three efficient isolates were Az14 (2.37 g l-1), Az20 (1.25 g l-1) from clay soil, Az6 (1.66 g l-1) from irrigation water. Also, it can be concluded that the optimal conditions for production of PHB from the most efficient Azotobacter sp. (Az14) were at 30 o C, pH 7, incubation time for 48 h, the best carbon source was starch at (1%) and ammonium sulphate at (0.2%) as nitrogen source. These optimal conditions lead to increase in the amount of PHB from 3.9 g l-1 to 5.31 g l-1 when using the inexpensive sources. So, these results lead to minimize the cost of production and increase the amount of PHB contribute to solving the environmental pollution problem.