Fig 1.
ABE fermentation performance with different operation strategies.
(A) ABE fermentation by C. acetobutylicum (control, case #a). (B) ABE fermentation by C. acetobutylicum with exogenous butyrate addition (case #b). (C) ABE fermentation by co-culturing C. acetobutylicum/S. cerevisiae (case #c). (D) ABE fermentation by co-culturing C. acetobutylicum/S. cerevisiae in coupling with exogenous butyrate addition (case #d). ●: butanol; ■: acetone; ▲: ethanol; ▽: butyrate; ○: glucose. (E)-(F) Change patterns of pH and gas production with different operation strategies. Thin line: case #a (control); dash dot line: case #b; broken line: case #c; bold line: case #d. Dashed arrow: the instant of initiating the consecutive butyrate additions (case #b); solid arrow: the instant of adding S. cerevisiae culture broth (case #c) and S. cerevisiae culture broth/concentrated butyrate solution (case #d).
Table 1.
Comprehensive performance comparison of ABE fermentation using different operation strategies.
Fig 2.
Amino acids secretion patterns with different operation strategies.
(A) ABE fermentation by C. acetobutylicum (control, case #a). (B) ABE fermentation by C. acetobutylicum with exogenous butyrate addition (case #b). (C) ABE fermentation by co-culturing C. acetobutylicum/S. cerevisiae (case #c). (D) ABE fermentation by co-culturing C. acetobutylicum/S. cerevisiae in coupling with exogenous butyrate addition (case #d). Black: lysine; white: methionine; horizontal shadow: phenylalanine; slashed shadow: tyrosine.
Fig 3.
Theoretical analysis results of the major secondary parameters associated with ABE fermentation performance when using different operation strategies.
(A) Contribution ratio of ethanol production by C. acetobutylicum. Thin line: ABE fermentation by C. acetobutylicum (control, case #a) and ABE fermentation by C. acetobutylicum with exogenous butyrate addition (case #b); broken line: ABE fermentation by co-culturing C. acetobutylicum/S. cerevisiae (case #c); bold solid line: ABE fermentation by co-culturing C. acetobutylicum/S. cerevisiae with butyrate addition (case #d). (B) Ethanol synthesis by C. acetobutylicum (EtOHCA). ■: case #a (control); ○: case #b; broken line: case #c; bold solid line: case #d. (C)-(D) Change patterns of rGLCCA and rNADHBtOH. ■: case #a (control); ○: case #b; ▲: case #c; ●: case #d.
Fig 4.
Investigation of interactions and dynamic behaviors of S. cerevisiae and C. acetobutylicum under each stress environments.
(A) Cells growth and ethanol synthesis in S. cerevisiae cultivation. Horizontal shadow: Initial cells concentration (OD600); slashed shadow: increased cells concentrations (OD600); white: ethanol concentration. (B) The concentrations of the four amino acids favorable for C. acetobutylicum survival and butanol synthesis in S. cerevisiae cultivation. Black: lysine; white: methionine; horizontal shadow: phenylalanine; slashed shadow: tyrosine. None and B&B referred to the cases of no any ingredients additions and simultaneously adding butanol and butyrate, respectively. (C) Impacts of exogenous ethanol addition on ABE fermentation by C. acetobutylicum. Black: butanol; white: acetone; slashed shadow: ethanol produced by C. acetobutylicum; horizontal shadow: added ethanol; ●: gas production amount. EtOH5 and EtOH10: 5 g-ethanol/L and 10 g-ethanol/L were added. (A)-(B) S. cerevisiae seeds were incubated in a rotating shaker at 200 r/min and 30°C for 24 h and then transferred into the anaerobic bottles. The cultivation continued for 36 h. (C) The fermentations ended at 60 h, ethanol was added at 24 h.
Fig 5.
Simplified metabolic network map indicating C. acetobutylicum and S. cerevisiae metabolisms.
Bold solid lines: enhanced metabolic fluxes; broken lines: weakened metabolic fluxes; dotted red lines: accumulation/secretion and assimilation/utilization directions of the amino acids favorable for butanol synthesis by C. acetobutylicum and C. acetobutylicum survival.
Fig 6.
S. cerevisiae cells viability and theoretical glucose amount consumed by S. cerevisiae in the proposed co-culturing system.
○ & ●: cell viability of S. cerevisiae in the co-culturing system without/with butyrate addition; □ & ■: theoretical glucose amounts consumed by S. cerevisiae in the co-culturing system without/with butyrate addition.
Fig 7.
Morphological shapes of C. acetobutylicum and S. cerevisiae in pure cultivations and the proposed co-culturing system with/without exogenous butyrate addition.
(A)-(B) The morphological shapes of C. acetobutylicum in pure C. acetobutylicum cultivation. (C)-(D) The morphological shapes of S. cerevisiae in pure S. cerevisiae cultivation (37°C). (E)-(F) The morphological shapes of C. acetobutylicum and S. cerevisiae in the co-culturing system without exogenous butyrate addition. (G)-(H) The morphological shapes of C. acetobutylicum and S. cerevisiae in the co-culturing system with exogenous butyrate addition.
Table 2.
Performance comparisons of ABE fermentations by butyrate supplementing or/and various co-culturing systems.
Table 3.
Economical evaluation of the proposed fermentation strategy using synthetic butyrate and butyrate fermentative supernatant.