Abstract
Microbial production of fuels and commodity chemicals has been performed primarily using natural or slightly modified enzymes, which inherently limits the types of molecules that can be produced. Type I modular polyketide synthases (PKSs) are multi-domain enzymes that can produce unique and diverse molecular structures by combining particular types of catalytic domains in a specific order. This catalytic mechanism offers a wealth of engineering opportunities. Here we report engineered microbes that produce various short-chain (C5–C7) ketones using hybrid PKSs. Introduction of the genes into the chromosome of Streptomyces albus enables it to produce >1 g · l−1 of C6 and C7 ethyl ketones and several hundred mg · l−1 of C5 and C6 methyl ketones from plant biomass hydrolysates. Engine tests indicate these short-chain ketones can be added to gasoline as oxygenates to increase the octane of gasoline. Together, it demonstrates the efficient and renewable microbial production of biogasolines by hybrid enzymes.
Highlights
Microbial production of fuels and commodity chemicals has been performed primarily using natural or slightly modified enzymes, which inherently limits the types of molecules that can be produced
We found that the employment of an alternative translational start site (TSS) in LipPks[1] dramatically increased the protein level of LipPks1 + TE and the corresponding product levels, 3-hydroxy acids, in a heterologous Streptomyces host, Streptomyces venezuelae ATCC 10712, compared to the originally annotated start codon[20]
Using the newly identified TSS, which truncates a part of the N-terminal tail of LipPks[1], we redesigned the ketone polyketide synthases (PKSs) genes (Fig. 1)
Summary
Microbial production of fuels and commodity chemicals has been performed primarily using natural or slightly modified enzymes, which inherently limits the types of molecules that can be produced. The resulting ethyl and methyl ketone PKS genes (Fig. 1 and Supplementary Data 1) were introduced into the chromosome of four Streptomycetes, and short-chain ketone-production levels were determined as discussed below.
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