High Production of Nattokinase via Fed-Batch Fermentation of the γ-PGA-Deficient Strain of Bacillus licheniformis

Abstract

During the production of nattokinase (NK) by Bacillus species, certain by-products such as poly-γ-glutamic acid (γ-PGA) are simultaneously synthesized. The impact of γ-PGA synthesis on NK production remains unclear. In this study, we knocked out the pgsC gene, a component of the γ-PGA synthetase cluster (pgsBCA), and constructed a novel recombinant strain, Bacillus licheniformis BL11. Next, we compared the fed-batch fermentation profiles of BL11 and its parental strain BL10, conducted transcriptional analysis, and measured intracellular ATP content. We also optimized glucose-feeding strategies under varying oxygen supply conditions. Our results indicated that the utilization rates of glucose and soybean meal were both improved in the pgsC-deficient strain BL11, and NK activity was enhanced. Furthermore, the transcriptional levels of genes involved in glycolysis and the TCA cycle were relatively upregulated in BL11. The maximal NK activity reached 2522.2 FU/mL at 54 h of fermentation using a constant glucose-feeding rate of 5.0 g/(L·h) under high oxygen supply conditions. The newly developed recombinant strain B. licheniformis BL11, along with the optimized feeding strategy, shows promise for large-scale NK production.