Optimisation of Poly(γ-Glutamic Acid) Production by Bacillus velezensis NRRL B – 23189 in Liquid Fermentation with Molasses as the Carbon Source without Addition of Glutamic Acid

Abstract

Poly (γ-glutamic acid), also known as γ-PGA, is an extracellular polymer produced by microbial fermentation. It is water-soluble, edible, biodegradable, non-toxic towards humans and the environment, and it has many available sites for drug conjugation and a powerful ability to solubilise hydrophobic molecules. This work reports the application of molasses, citric acid and ammonium sulphate in the fermentation by Bacillus velezensis NRRL-23189 to produce γ-PGA and the detection of molasses consumption without the use of glutamic acid as a nutrient. Different concentrations of molasses, citric acid and ammonium sulphate were studied. The fermentation was agitated at 200 rpm at 27oC for 72 h, with an initial pH of 6.5 (NaOH 2N and HCl 2N). Spectrophotometric analyses were used to measure concentrations of γ-PGA and the residual sugar from molasses degradation. The maximum production of γ-PGA was 4.82 g/l, in a medium with molasses (200g/l), citric acid (12.5g/l) and ammonium sulphate (8g/l) in a fermentation that also resulted in the maximum sugar consumption.