Reconstruction of metabolic pathways for cadaverine production from galactose in Escherichia coli

Abstract

Biological production of cadaverine has recently come into the spotlight as an alternative to replace synthetic polymers generated from the petroleum-based process due to increasing environmental problems and the sustainability of resources. To establish an ideal bioprocess, cadaverine should be produced with high yield and productivity from various sugars abundant in biomass. However, most microorganisms are not able to efficiently metabolize other biomass-derived sugars as fast as glucose. This results in reduced growth rate and low carbon flux toward the production of desired bio-chemicals. Thus, reconstructing genetic networks is necessary for utilizing those carbon sources with enhanced carbon flux and product formation. In this study, the novel Escherichia coli was developed to produce cadaverine with rapid assimilation of galactose, a promising future feedstock. To achieve this, metabolic pathways were redesigned to amplify the carbon flux toward cadaverine production with maximum level using the redesigned expression cassettes consisting of predictive and quantitative genetic parts (promoters, 5′-untranslated regions, and terminators). Furthermore, the feedback inhibition of metabolic enzymes and degradation/re-uptake pathways were inactivated to robustly produce cadaverine. Finally, the resultant strain, DHK4 showed high titer (8.80 g/L), yield (0.170 g/g), and productivity (0.293 g/L/h) during fed-batch fermentation, which was similar or better than the glucose-based fermentation. As a results, it was revealed that the genetic engineering of a microorganism was a prerequisite to be the ideal fermentation process converting the promising sugar into desired a platform chemical. This is the first report to make cadaverine from galactose. Moreover, the yield (0.170 g/g) was the highest ever reported, including that from glucose in E. coli.