Microbial biopolymer production by Microbacterium WA81 in batch fermentation

• Microbial Biopolymer produced by a potential novel strain was optimized.
• Optimization was performed by applying Statistical Design of Experiment Methodology.
• The most potential Carbon and Nitrogen sources were exposed to a Central Composite Design to determine the optimum combination.
• The generated medium was applied to Bioreactor batch run which led to a 78 fold increase in the amount of Biopolymer.
• Dissolved oxygen was found to inhibit the biopolymer synthesis in the Bioreactor Environment.

Microbial Poly-β-hydroxybutyrate (PHB) was the first and the most widespread polymer to be used in the biodegradable polymer industry. The optimization of the Egyptian local bacterial strain Microbacterium sp. WA81 productivity was performed using statistical design of experiment tools. A Plackett–Burman design was carried out to screen the effect of different carbon and different nitrogen sources, each in a separate experiment. Moreover, a subsequent Response Surface Methodology was applied to achieve the maximum PHB productivity at shake flask level. Upon scaling up to a bench top bioreactor run scale (5 L), using the generated medium, the amount of the polymer significantly increased (1.42 g/L), which represented a 78-fold increase of that prior optimization. During the bioreactor run, the preliminary effect of Dissolved Oxygen (DO) was explored, and the levels of carbon and nitrogen uptakes were monitored. In conclusion, the statistical design of experiment tools enabled us to optimize and engineer a growth medium and conditions to enhance PHB productivity by the Egyptian isolate Microbacterium sp. WA81.