Production and optimization of polyglutamic acid from Bacillus licheniformis: effect of low levels of gamma radiation

Polyglutamic acid (PGA), has several beneficial characteristics and advantageous uses. The microbial biopolymer is released from a variety of organisms, particularly Bacillus species. Soil samples from various sectors of Egypt were gathered and evaluated for the production of PGA. According to the current study results, isolate (L) was the most powerful producer and was identified by 16S rRNA as Bacillus licheniformis. A multi-factorial Plackett-Burman layout was used to optimize PGA bacterial synthesis. Mass spectrometry, thin-layer chromatography, Fourier transform infrared spectroscopy (FTIR), and amino acid analysis were employed to characterize the product. It was also investigated how the produced polymer was affected by low gamma irradiation doses. In comparison to Bacillus subtilis (ATCC6633), Bacillus licheniformis showed an over 33% inclination in PGA yield under optimal conditions. FTIR spectra demonstrated that PGA functional groups were successfully unchanged after exposure to low levels of gamma radiation similar to the doses given to cancer patients under radiotherapy. Thermal Gravimetric Analysis (TGA) showed 2 phase weight loss for gamma irradiated PGA, emphasizing that the polymer showed thermal stability after exposure to gamma radiation. These results were confirmed by Dynamic light scattering (DLS) and liquid chromatography mass spectrometry. Finally, the isolated Bacillus licheniformis strain can be considered as a prospective source of PGA for future industrial and medicinal uses. Additionally, this could be a promising result for the use of PGA as a drug carrier for cancer patients undergoing radiation therapy.