Enhanced poly(γ-glutamic acid) fermentation by Bacillus subtilis NX-2 immobilized in an aerobic plant fibrous-bed bioreactor

• Aerobic fibrous-bed bioreactor using bagasse as immobilized carrier was designed.
• The time of immobilization fermentation is 48 h while free-cell 72 h.
• PGA yield of 71.21 g/L was achieved by repeated fed-batch fermentation in APFB.
• We evaluated the stability of the APFB system.
• The changes in the cells of free and immobilized cell fermentation were compared.

To enhance poly(γ-glutamic acid) (PGA) production, a novel aerobic plant fibrous-bed bioreactor (APFB) was constructed for immobilized fermentation. Based on the analysis of the kinetics of immobilized-cell fermentation using the APFB and conventional free-cell fermentation, immobilized-cell fermentation exhibited more efficient PGA production. Furthermore, repeated fed-batch cultures for PGA production were conducted to evaluate the stability of the APFB system. Average final PGA concentration and productivity of 71.21 ± 0.83 g/L and 1.246 ± 0.008 g/L/h were respectively achieved by cells immobilized in bagasse during APFB, which was reused eight times over a period of 457 ± 18 h. Analysis of the membrane phospholipids and the key enzyme activities indicated that APFB-adapted cells had better productivity than original cells. Thus, this study demonstrated the significant potential of the APFB culture system in future industrial applications.