title: Metabolic engineering of Methylobacterium extorquens AM1 for 1-butanol production.
abstract: BACKGROUND
  Butanol is a promising next generation fuel and a bulk chemical precursor. Although clostridia are the primary industrial microbes for the fermentative production of 1-butanol, alternative engineered hosts have the potential to generate 1-butanol from alternative carbon feedstocks via synthetic metabolic pathways. Methylobacterium extorquens AM1, a facultative methylotrophic α-proteobacterium, is a model system for assessing the possibility of generating products such as 1-butanol from one-carbon and two-carbon feedstocks. Moreover, the core methylotrophic pathways in M. extorquens AM1 involve unusual coenzyme A (CoA)-derivative metabolites, such as crotonyl-CoA, which is a precursor for the production of 1-butanol.
  
  
  RESULTS
  In this work, we engineered a modified CoA-dependent pathway in Methylobacterium extorquens AM1 to produce 1-butanol. Engineered strains displayed different 1-butanol titers using ethylamine as a substrate. A strain overexpressing Treponema denticola trans-enoyl-CoA reductase, Clostridium acetobutylicum alcohol dehydrogenase, and native crotonase was able to generate the highest 1-butanol titer (15.2 mg l(-1)). In vitro isotopic tracing of metabolic flux and in vivo metabolite analysis showed the accumulation of butyryl-CoA, demonstrating the functionality of the synthetic pathway and identifying targets for future improvement.
  
  
  CONCLUSIONS
  We demonstrated the feasibility of using metabolic intermediates of the ethylmalonyl-CoA pathway in M. extorquens AM1 to generate value-added chemicals, with 1-butanol as the test case. This will not only establish the biotechnological potential of the ethylmalonyl-CoA pathway, but will also introduce M. extorquens AM1 as a potential platform to produce value-added chemicals.
authors.affiliation: Department of Chemical Engineering, University of Washington, Seattle, WA USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Hu
authors.affiliation: Department of Chemical Engineering, University of Washington, Seattle, WA USA ; Department of Microbiology, University of Washington, Seattle, WA 98195-1750 USA.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Lidstrom
keywords: 1-butanol; Ethylmalonyl-CoA pathway; Methylobacterium extorquens AM1