Researchers at Beijing University of Chemical Technology have engineered Klebsiella pneumoniae—a pathogen—to produce 1-butanol. A paper on their work appears in the ACS journal Energy & Fuels.
Although K. pneumoniae is a pathogenic microorganism, it has been studied widely because of its ability to metabolize glycerol and its similar genetic background to E. coli. Glycerol is being abundantly and increasingly produced as a byproduct of biodiesel production and in thus an abundant bioresource feedstock to produce valuable chemicals; K. pneumoniae is thus a potentially attractive host to produce 1-butanol, the researchers said.
There are two distinct pathways to synthesize 1-butanol in bacteria: CoA-dependent and Ehrlich. The Ehrlich pathway has several advantages over the CoA- dependent pathway, the researchers said, and more importantly, it circumvents the production of some toxic metabolites, especially CoA-dependent intermediates.
The 1-butanol producer, recombinant Klebsiella pneumoniae (KLA), was constructed by overexpressing the genes kivd, leuABCD, and adhE1 under the control of tac promoter in this study, and several NADH regeneration strategies were adopted to solve the problem of NADH imbalance, including the introduction of NAD+-dependent enzymes (formate dehydrogenase, pyridine nucleotide transhydrogenase, and glucose dehydrogenase) or elimination of the NADH competition pathway (1,3-propanediol synthesis).
The resultant NADH/NAD+ ratio, 1-butanol production, and transcription levels have been significantly affected. In comparison to the wild-type strain, the NADH/NAD+ ratio in the reengineered strains was increased by 78–135%, and the transcript levels of target genes have been obviously interfered. Moreover, the resultant 1-butanol titer was increased by 83–114% in comparison to KLA. [The final 1-butanol titer for KLA, pre NADH strategies, was 58 mg/L, Ed.]—Wang et al.
Miaomiao Wang, Lijuan Hu, Lihai Fan, and Tianwei Tan (2015) “Enhanced 1-Butanol Production in Engineered Klebsiella pneumoniae by NADH Regeneration” Energy Fuels doi: 10.1021/acs.energyfuels.5b00009