Table 1 Summary of main challenges and solutions for fermentative butanol production
| Challenge | Suggested solution |
|---|---|
| High substrate cost |
Lignocellulosic substrates [3, 12,13,14,15, 18, 23, 29, 31,32,33,34,35] Starch based waste [12, 29, 33] Syngas [12, 23, 24, 33, 35] Macroalgae [12, 16, 23] Crude glycerol [12, 23, 24, 31] Protein waste [23] Whey permeate [14, 29, 34] Economical feedstock processing methods [3, 18, 29] Medium optimization [18, 28] Inulin [31] |
| Low butanol selectivity |
Metabolic engineering for disruption of the pathway for acetone [3, 13,14,15, 23, 25, 27, 32, 34] Homo-butanol fermentation via chemical mutagenesis and metabolic engineering [23, 24, 33, 35] Conversion of acetone into isopropanol [13, 15, 23] Decoupling sporulation from solventogenesis [3, 13, 14, 23, 25, 27, 28, 34, 35] |
| Low butanol titer |
Metabolic engineering and mutagenesis for higher butanol tolerance [13,14,15, 21, 23,24,25, 27, 28, 32,33,34,35] In situ product removal [3, 12,13,14,15, 18, 22, 23, 27, 28, 32, 34, 35] Introducing butanol pathways in other hosts [3, 13, 15, 21, 23,24,25, 27, 33,34,35] Re-enforcing hot channel for butanol formation [14] |
| Low butanol yield |
Simultaneous utilization of mixed sugars in the hydrolysate without Carbon Catabolite Repression [14, 23, 31] Extending the substrate utilization range [15, 34, 35] |
| Low butanol productivity |
Simultaneous utilization of mixed sugars without Carbon Catabolite Repression [3, 23, 28, 29] Fed-batch fermentation [3, 12, 14, 18, 34] Chemostat/continuous culturing [3, 12,13,14,15, 18, 32, 34] Immobilized cell chemostat [3, 12,13,14,15, 18, 34] Cell recycle chemostat [3, 12,13,14,15, 18, 34] Multi stage chemostat [3, 13, 14, 18] |
| Low O2 tolerance |
Co-culturing to maintain anaerobic conditions [32] Random mutagenesis and selection [13, 35] Metabolic engineering [27, 36] |
| Culture degeneration | Prevention of excessive acidification of the culture [35] |
| Phage contamination | Good factory hygiene, strains immune to specific phages [27, 35] |