Enhanced protein-glutaminase production from Chryseobacterium proteolyticum by the addition of leucine

Abstract

Protein-glutaminase (EC 3.5.1.44, PG) derived from Chryseobacterium proteolyticum can significantly improve the solubility, emulsification and foaming properties of food proteins and is a promising deaminase. PG has broad application prospects in the food industry. However, the low yield of the enzyme is not sufficient for industrial applications. Mutagenesis and molecular breeding can improve PG yield, which consumes considerable time and has high costs. In contrast, it is a feasible way to achieve high PG yields to optimize the fermentation conditions of the strains. In this work, amino acids were screened to improve PG production. The addition of 0.80 g/L leucine (Leu) could increase PG production by 27.80%. Then, through the response surface method, it was found that under the combination of 1.60 g/L Leu, 5.65 g/L MgSO4.7 H2O and 5.13 g/L KH2PO4, PG production reached 2.93 U/mL, which was 1.87 times that of the original medium. The growth and metabolism curves of Chryseobacterium proteolyticum were measured under this formula. The effect of Leu on PG production was further investigated by measuring the transcription of the PG gene, the conductivity of fermentation fluid and the morphological characteristics of cells. This work lays a foundation for the industrial production of PG.