Butanol and isobutanol production

Trinh, C.T. (2012) Elucidating and reprogramming Escherichia coli metabolisms for obligate anaerobic n-butanol and isobutanol production. Appl Microbiol Biotechnol, 95, 1083-1094. 

Trinh C (2012) Elucidating and optimizing E. coli metaboUsms for obUgate anaerobic butanol and isobutanol production. Appl Microbiol Biotechnol 95(4) 1083-1094 Trinh CT, Srienc F (2009) Metabolic engineering of Escherichia coli for efficient conversion of glycerol to ethanol. Appl Environ Microbiol 75 6696-6705 Trinh CT, Carlson R, Wlaschin A, Srienc F (2006) Design, construction and performance of the most efficient biomass producing E. coli bacterium. Metab Eng 8 628-638 Trinh CT, Unrean P, Srienc F (2008) Minimal Escherichia coli ceU for the most efficient production of ethanol from hexoses and pentoses. Appl Environ Microbiol 74 3634-3643... 

Fatehi, P. (2013) Recent advancements in various steps of ethanol, butanol, and isobutanol productions from woody materials. Biotechnol Progr., 29, 297-310. 

There are different tactics in the metabolic engineering of heterotrophic microbes for butanol and isobutanol production. Even though new methods are being examined intensively, engineered metabolic pathways for production of butanol can be classified in three groups ... 

Production. Although the patent literature cites many other amino and amide compounds, only urea, melamine, benzoguanamine, acrylamide, and glycoluril have found a market position as starting materials for the production of amino resins. Formaldehyde is the only aldehyde used on a commercial scale. Methanol, butanol, and isobutanol are mainly employed as alkylating alcohols. 

Fermentative production of butanol and isobutanol is not yet competitive to the petrochemical production route. Yet, intensive research in the last years is slowly but constantly closing the gap between the two processes. 

Subsequently, a whole host of both lower (C3, C4, C5) and higher (C5, Cy, C9, C q, C, etc.) oxo alcohols have been commercialized. Of all these alcohols, the most important by far have turned out to be n-butanol and 2-ethylhexanol - both of which are derived from n-butyraldehyde based on hydroformylation of propylene. In addition to n-butyraldehyde, the lower valued isobutyraldehyde is produced as a by-product. Some of this is converted to isobutanol. 

In substrate selectivity, access to the catalytically active site is restricted to one or more substrates present in a mixture, e.g. dehydration of a mixture of n-buta-nol and isobutanol over the small pore zeolite, CaA, results in dehydration of only the n-butanol [38] while the bulkier isobutanol remains unreacted. Product... 

Table 9.9 lists the commercial specifications of butanols. Tables 9.10 and 9.11 give the uses and production of n-butanoi and isobutanol for Western Europe, the United States and Japan in 1984. 

Figure 5.2 Isobutanol production via vaiine pathway and 1-butanol production via CoA-dependent pathway implemented. Common enzyme abbreviations or gene symbols ilvIH, acetolactate synthase ( . coli) aIsS, aceto-lactate synthase (Bacillus subtilis) ilvC, ace-tohydroxy acid isomeroreductase ( . coli) ilvD, dihydroxy acid dehydratase ( . coli) kivd, ketoisovalerate decarboxylase (Lactoccus...

Methyl-butanol (2MB) is synthesized via the isoleucine pathway (Figure 15.4), which is similar to the valine biosynthesis pathway. One of the challenges for 2MB production is that it passes over the same cassette of genes as in isobutanol production. A recent study [106] indicated that enhancing the citramalate pathway to direct the carbon flux from pyruvate to a-ketobutyrate led 2MB production to about 200 mg 1" with minimum side products such as 1-propanol and isobutanol. 

Synthesis gas, a mixture of mainly CO, CO2, and H2, has been used in chemical industry as feedstock and can be generated by gasification of coal and oil but also from biomass, municipal waste, or by recycling of used plastics (Kopke et al., 2010). Isobutanol production from synthesis gas has so far not been reported. However, Kopke et al. (2010) engineered Clostridium ljungdahlii, which is naturally able to use synthesis gas as carbon and energy source, for the production of 1-butanol by implementation of the CoA-dependent 1-butanol synthesis pathway from Clostridium acetobutylicum. The final titer of about 0.5 mM 1-butanol was rather low however, this approach demonstrated the feasibility to produce fuels and chemicals from synthesis gas. 

Butanol has been synthesized in various organisms through different pathways. The CoA-dependent pathway from Clostridium and its variations (Figure 19.1) are the best studied [65]. This pathway is chemically similar to the reversal of P-oxidization [66, 67]. The intrinsic iteration nature of reverse p-oxidization also enables the biosynthesis of longer chain alcohols, for example, -hexanol and n-octonol [66]. The citramalate and threonine pathways fall into the same broad group as the keto-acid pathway (Figure 19.2), which is more commonly utihzed for isobutanol production. 

The relatively high-level isobutanol production using the amino acid pathway shows the potential of this strategy and small stepwise optimisation. This versatile approach was used for production of 1-butanol (Atsumi et al. 2008a) over the norvaline biosynthesis pathway, which is a minor side reaction of leucine biosynthesis (Connor and Liao 2009). 

Butanol Production via Norvaline Pathway Besides isobutanol it is possible to use the amino acid pathways to produce 1-butanol and 1-propanol that share a conmiOTi precursor— threonine. 

Within the reactor, however, 6 per cent of the n-butyraldehyde product is reduced to n-butanol, 4 per cent of the isobutyraldehyde product is reduced to isobutanol, and other reactions occur to a small extent yielding high molecular weight compounds (heavy ends) to the extent of 1 per cent by weight of the butyraldehyde/butanol mixture at the reactor exit. 

In hydrocarbons a variety of by-products was formed. Propylene oxide gave some j8-hydroxyisobutyraldehyde as well as the normal product, also acetone, isobutyraldehyde, methacrolein, n-butyraldehyde, isobutanol, crotonaldehyde, and n-butanol. Presumably these by-products were formed by dehydration and hydrogenation of the hydroxyaldehydes, except for acetone which was formed by isomerization. The side reactions can be kept to a minimum by operating below 95° C (160). Fewer by-products appear to be formed using alcohols as solvents. Using methanol, Eisenmann (24) noted that carbon monoxide had an inhibitory effect at high pressures. 

Fusel alcohols (1-propanol, 2-methyl-1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-phenyl-ethanol) were actually among the first aroma constituents studied, as early gas chromatographic research had indicated, erroneously, that these compounds represented the predominant volatile fraction in wines (28). Yeast-specific fusel alcohol production has been studied by a number of researchers (31,33,37-39), all of whom found production differences among yeast strains. Unfortunately yeast strains have not usually been replicated among studies an exception is the work of Delteil and Jarry (57) and Kunkee and Vilas (39). Their results for the fiisel alcohol isobutanol (2-methyl-1-propanol) are shown in Table I. Soufleros and Bertrand (55) studied fifty different yeast strains unfortunately their data do not allow for statistical analysis. Mateo and coworkers (38) examined ten... 

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