초록
<P><B>Background</B></P><P>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. <I>Methylobacterium extorquens</I> 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 <I>M. extorquens</I> AM1 involve unusual coenzyme A (CoA)-derivative metabolites, such as crotonyl-CoA, which is a precursor for the production of 1-butanol.</P><P><B>Results</B></P><P>In this work, we engineered a modified CoA-dependent pathway in <I>Methylobacterium extorquens</I> AM1 to produce 1-butanol. Engineered strains displayed different 1-butanol titers using ethylamine as a substrate. A strain overexpressing <I>Treponema denticola</I> trans-enoyl-CoA reductase, <I>Clostridium acetobutylicum</I> alcohol dehydrogenase, and native crotonase was able to generate the highest 1-butanol titer (15.2 mg l<SUP>−1</SUP>). <I>In vitro</I> isotopic tracing of metabolic flux and <I>in vivo</I> metabolite analysis showed the accumulation of butyryl-CoA, demonstrating the functionality of the synthetic pathway and identifying targets for future improvement.</P><P><B>Conclusions</B></P><P>We demonstrated the feasibility of using metabolic intermediates of the ethylmalonyl-CoA pathway in <I>M. extorquens</I> 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 <I>M. extorquens</I> AM1 as a potential platform to produce value-added chemicals.</P>