Developing Novel Pathways for Butanol Production in E. coli
In the biofuels market, n-butanol has been gaining attention due to its superior fuel properties when compared with ethanol. Although n-butanol is naturally produced by solventogenic bacteria through ABE fermentation, the low productivities obtained with this bioprocess discouraged its use. Thus, most n-butanol produced nowadays is chemically synthesized via petrochemical routes. One possible alternative is to express non-native pathways in microbial factories.
Our work focuses on the production of butanol through heterologous pathways, previously generated within our group  using a (hyper)graph-based algorithm, in Escherichia coli. First, we evaluated these pathways according to diverse criteria including the number of biochemical steps required, maximum yield, conservation of carbon atoms and novelty. A novel pathway generated by the algorithm, which is significantly different from the available in solventogenic bacteria, was then introduced in a genome-scale model of E. coli (iJO1366) and the production of butanol was optimized in silico using Optflux (http://www.optflux.org), a software platform for metabolic engineering. Several different environmental conditions and sets of gene knock-outs were evaluated with the aim of redirecting the cell metabolism to solvent production. The biological significance of the predicted phenotypes was analyzed to rationally design a strain that couples growth and butanol production.
Using biomolecular techniques, a novel strain of E. coli – able to produce butanol through the selected pathway in the same conditions simulated in silico– is currently being constructed.
 F. Liu, P. Vilaça, I. Rocha, and M. Rocha, “Development and application of efficient pathway enumeration algorithms for metabolic engineering applications,” Comput. Methods Programs Biomed., Dec. 2014.