Chapter 2. Literature Review 9
2.2 Acetone-Butanol-Ethanol (ABE) fermentation
2.2.4 Factors affecting growth and solvent production
Marine macroalgae (seaweeds)
Marine macroalgae usage as a substrate for biofuel production has many key advantages such as high carbohydrate composition, low lignin content, and no need for arable land for cultivation (Ohgren et al., 2007; Wargacki et al., 2012).
The key hindrance in efficient utilization of marine macroalgae is the presence of sugars such as L-rhamnose, 3, 6-anhydro-L-galactose (AHG), and 4-deoxy-L-erythro- 5-hexoseulose (DEH). These sugars are non-fermentable by clostridia (van der Wal et al., 2013; Yun et al., 2015) and thus wild type strains have to be genetically engineered to render them capable for bioprocess development utilizing macroalgae.
Syngas
Mixture of CO, CO2, and H2 gases is designated as syngas. Syngas is mainly produced from carbon based materials such as natural gas, coal, biomass, and waste by a process known as gasification (Basu, 2018). Utilization of syngas as a carbon source for biofuel production (Weissermel and Arpe, 2008) is not only a cost-effective alternative but also makes way for environmental benefits. Clostridial spp. such asC.
glycolicum,C. ljungdahli,C. autoethanogenum, andC. carboxidivorans( Köpke et al., 2010; Bruant et al., 2010; Guo et al., 2010; Fernández-Naveira et al., 2017; Küsel et al., 2001) are able to ferment syngas. However, onlyC. carboxidivoranshas been reported to produce butanol (Fernández-Naveira et al., 2017) since others lack the butanol synthesis genes required to produce butanol using syngas (Guo et al., 2010;
Köpke et al., 2010). The Wood-Ljungdahl (WL) pathway is functional in species utilizing syngas with the first step in WL pathway involving the conversion of CO or CO2 plus H2 to produce acetyl-CoA. Acetyl-CoA serves as the common branching point for both the acid and alcohol synthesis pathways (Drake et al., 2008).
Table 2.3. Different environmental cues affecting growth and solvent production inClostridiumsp.
Factors Organism Mode of cultivation Remarks Reference
pH control Clostridium beijerinckiiIB4 Batch Improved butanol titer Jiang et al., 2014
pH control C. acetobutylicumATCC 824 Batch Improved butanol titer Monot et al., 1984
pH control C. acetobutylicumXY16 Batch improved solvent production Guo et al., 2012
pH control C. acetobutylicumATCC 824 Batch Improved butanol titer Yang et al., 2013
Sodium butyrate
supplementation Clostridium beijerinckiiNCIMB 8052 Batch Improved butanol titer and butanol selectivity Wang et al., 2013
Sodium butyrate Clostridium beijerinckiiNCIMB 8052 Batch Improved butanol yield Lee et al., 2008b
Butyric acid addition C. saccharoperbutylacetonicumN1-4 Fed-batch Improved yield and butanol titer Tashiro et al., 2004 Butyric acid addition C. acetobutylicumATCC 824 Batch Improved butanol selectivity and 2% increase in
butanol titer Martin et al., 1983
Butyric acid addition C. acetobutylicumATCC 39236 Batch Improved butanol titer Datta and Zeikus, 1985
Glucose
concentration C. acetobutylicumATCC 824 Batch Improved butanol titer Monot et al., 1982
Phosphate limitation C. acetobutylicum Chemostat Solventogenesis at low pH Bahl and Gottschalk, 1985
Sulphate limitation C. acetobutylicum Chemostat Solventogenesis at low pH Bahl and Gottschalk, 1985
Magnesium
limitation C. acetobutylicum Chemostat Not appropriate for continuous Bahl and Gottschalk, 1985
Iron limitation C. beijerinckiiNCIB 8052 Batch Decrease in butanol titer but improved butanol
selectivity Junelles et al., 1988
Iron limitation C. pasteurianumDSM 525 Phosphate limited
chemostat Improved butanol titer Dabrock et al., 1992
Iron limitation C. acetobutylicum Chemostat B:A=8 (at low pH) Bahl et al., 1986
CO pressure C. acetobutylicumATCC 39236 Batch Improved butanol titer Datta and Zeikus, 1985
CO pressure C. pasteurianumDSM 525 Phosphate limited
chemostat Improved butanol titer Dabrock et al., 1992
Methyl Viologen
supplementation C. acetobutylicum Batch Improved butanol selectivity and butanol titer at
controlled pH of 5 Peguin et al., 1994
1 mM methyl
viologen C. acetobutylicumATCC 824 Batch Improved butanol selectivity and butanol titer Honicke et al., 2012 MV+Fe limitation C. acetobutylicum Batch Improved butanol titer at controlled pH of 5.5 Peguin and Soucaille, 1995 Whey fermentation C. acetobutylicum Continuous culture Decrease in butanol titer but improved butanol
selectivity Bahl et al., 1986
Redox control
(—290 mV, air) C. acetobutylicum Batch Improved solvent production Wang et al., 2012
Glycerol
supplementation C. beijerinckii Batch Improved furfural detoxification Ujor et al., 2014
Tiron
supplementation C. acetobutylicumYM1 Batch Improved solvent production Al-Shorgani et al., 2015
Furfural or HMF
supplementation C. beijerinckiiBA101 Batch Improved growth (13%) and solvent production
(19%) Ezeji et al., 2007
Furfural+HMF
supplementation C. beijerinckiiP260 Batch Improved ABE productivity Qureshi et al., 2012
ZnSO4
supplementation C. acetobutylicumL7 Batch Improved growth and butanol titer Wu et al., 2013
CaCO3
supplementation C. acetobutylicum Batch Improved growth, sugar uptake, solvents Li et al., 2013b
CaCO3
supplementation C. beijerinckiiNCIMB 8052 Batch Ameliorated LDMIC inhibition Zhang and Ezeji, 2014
CaCO3
supplementation C. acetobutylicum Batch Relieves carbon catabolite repression El Kanouni et al., 1998
CaCO3
supplementation C. sporogenesBE01 Batch Improved hydrogen, volatile fatty acids and
solvents Gottumukkala et al., 2015
Page|26 Department of Biosciences & Bioengineering|
TH-2103_126106021
shown improvement in the butanol titer and yield. Variations in growth media are also known to alter the dynamic solvent production profile. Long et al. (1984) observed that excess glucose was required for initiation of butanol production and limitations of phosphate improved the yield (Bahl and Gottschalk, 1985). Limitation of other media nutrients such as iron, magnesium, sulphate, and nitrogen have been shown to affect growth and solvent production inClostridiumsp. (Bahl et al., 1986;
Junelles et al., 1988; Peguin and Soucaille, 1995). In some cases ofC. beijerinckii cultivation, addition of furfural and/or 5-hydroxymethyl furfural was reported to improve growth and solvent production (Ezeji et al., 2007; Qureshi et al., 2012), whileC. acetobutylicumreportedly exhibited no change in fermentation profile (Zhang et al., 2012). Wu et al. (2013) reported that zinc supplementation to fermentation media improved clostridial growth and butanol production. Changes in incubation temperature, increased hydrogen partial pressure, and intermittent oxidative stress are also shown to affect butanol production (Jones and Woods, 1986).
Supplementation of electron carriers such as methyl/benzyl viologen or carbon monooxide gassing is shown to improve butanol selectivity (Kim and Kim, 1988;
Dabrock et al., 1992; Peguin et al., 1994; Honicke et al., 2012). Even though required in small amounts, electron carriers such as methyl/benzyl viologen are costly and would affect the process economics on large scale operation. On the other hand, carbon monooxide being a toxic gas poses environmental threat and would require additional precautionary measures when used in industry. Another important aspect is related to the maximum achievable butanol concentration which is restricted by butanol toxicity (Dunlop, 2011). Therefore, factors providing tolerance to the strain can also be targeted for improvement in the production capacity. On such inducer is calcium carbonate, which has been reported to improve butanol tolerance along with buffering capacity, increased substrate utilization, and efficient acid re-assimilation (Richmond et al., 2011; Han et al., 2013; Gottumukkala et al., 2015).