Production increasing of poly-γ-glutamic acid by batch and fed-batch cultures of Bacillus licheniformis ATCC 9945a and study of its physical and chemical structure

Poly-γ-glutamic acid (γ-PGA) is a beneficial, biocompatible, and biodegradable biopolymer. </font>These properties have been led to the development of the use of this compound in various industries such as bio-medicine, biopharmaceutical, biotechnology, and tissue engineering. The limitation of the industrial development of γ-PGA is the high cost of its production. To reduce γ-PGA production costs, various strategies are used, such as culture medium optimization using inexpensive compounds, the development of efficient cultivation processes of batch and fed-batch. In this research, first, an efficient batch culture medium was developed to produce γ-PGA of Bacillus licheniformis</em> ATCC 9945a</sup>. Then, the γ-PGA production increased by the pulsed feeding method and its optimization. By optimal culture medium development, the production of this product in batch culture was increased from 11 g/L to 47 g/L. Then, using the optimized pulsed feeding strategy of citrate (γ-PGA precursor), γ-PGA production was increased to 59.5 g/L, which is one of the highest production values reported with this strain. To optimize two-pulse feeding, the effect of feeding times, stock citrate solution concentration, and time of calcium and manganese solutions addition on γ-PGA production were investigated and optimized. Finally, FTIR confirmed the chemical structure of poly gamma glutamic acid, and the study of γ-PGA morphological properties with SEM showed a nanostructure ideal for biological applications.