shake flask experiment results showed that high concentration KCl had obvious effects on γ -PGA production. To evaluate
this in scale-up fermentation, the time courses of γ -PGA yield,
cell growth, broth viscosity, glucose and glutamate consumption
in 3.6-L fermentor without (Fig. 4A) or with (Fig. 4B) KCl were
investigated. Results showed that γ -PGA production in fermentor
was consistent with in shake flask. The maximum yield of γ -PGA
was obtained at 22 h regardless of A or B, but the yield in B was
25.62 ± 0.95 g/L with productivity 1.16 g/L · h, which was 1.4-fold
higher than that in A. Although the viable count decreased after
adding KCl, the maximum growth in B had been brought forward
to 16 h and had a marked effect in prolonging cell viability. However, it’s interesting that the glucose in A was consuming much
faster than in B, but the residual glutamate all remained about
6 g/L at the end of fermentation. The viscosity of broth decreased
sharply from 4289.5 ± 198.0 mPa · s in A to 748.0 ± 32.0 mPa · s
in B by 82.6%. These results indicated that KCl concentration was
one key influencing factor for γ -PGA production in B. subtilis. Thus,
adding KCl can be used as an effective strategy to control γ -PGA
fermentation.