Abstract
BackgroundPropane, a major component of liquid petroleum gas (LPG) derived from fossil fuels, has widespread applications in vehicles, cooking, and ambient heating. Given the concerns about fossil fuel depletion and carbon emission, exploiting alternative and renewable source of propane have become attractive. In this study, we report the construction of a novel propane biosynthetic pathway in Escherichia coli.ResultsWe constructed an aldehyde reductases (ALR)-deprived E. coli strain BW25113(DE3) Δ13 via genetic engineering, which produced sufficient isobutyraldehyde precursors and finally achieved de novo synthesis of propane (91 μg/L) by assembling the engineered valine pathway and cyanobacterial aldehyde-deformylating oxygenase (ADO). Additionally, after extensive screening of ADO mutants generated by engineering the active center to accommodate branched-chain isobutyraldehyde, we identified two ADO mutants (I127G, I127G/A48G) which exhibited higher catalytic activity for isobutyraldehyde and improved propane productivity by three times (267 μg/L).ConclusionsThe propane biosynthetic pathway constructed here through the engineered valine pathway can produce abundant isobutyraldehyde for ADO and overcome the low availability of precursors in propane production. Furthermore, the rational design aiming at the ADO active center illustrates the plasticity and catalytic potential of ADO. These results together highlight the potential for developing a microbial biomanufacturing platform for propane.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0496-z) contains supplementary material, which is available to authorized users.
Highlights
Propane, a major component of liquid petroleum gas (LPG) derived from fossil fuels, has widespread applications in vehicles, cooking, and ambient heating
Biosynthesis of isobutyraldehyde, the precursor for propane production First, an isobutyraldehyde synthetic pathway was constructed based on the valine pathway of E. coli [15, 16]
In the last two steps, Kivd from Lactococcus lactis transformed 2-ketoisovalerate into isobutyraldehyde, which could be converted into propane further by the aldehyde-deformylating oxygenase (ADO) from Prochlorococcus marinus MIT 9313
Summary
A major component of liquid petroleum gas (LPG) derived from fossil fuels, has widespread applications in vehicles, cooking, and ambient heating. Propane has become a promising fuel due to its remarkable properties such as higher energy density and liquefaction point than hydrogen, cleaner combustion and less greenhouse gas emission than gasoline, and compatibility with existing engine systems and transportation infrastructures [1] It has been widely used in vehicle engines, cooking, and ambient heating [2]. The pathway with best performance contains acetyl-CoA acetyltransferase (AtoB) from E. coli, 3-hydroxybutyryl-CoA dehydrogenase (Hbd) and 3-hydroxybutyryl-CoA dehydratase (Crt) from Clostridium sp., NADH-dependent transenoyl-CoA reductase (Ter) from Treponema denticola, thioesterase (YciA) from Haemophilus influenza, and CAR from M. marinum These enzymes catalyze a series of reactions similar to those of the first propane pathway and convert acetyl-CoA into propane through CoAdependent pathway instead of ACP-dependent FASII pathway (blue part of Fig. 1)
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