(63d) Polyketide Synthases As a Platform for Biofuel Production

With the rise of greenhouse gases and the severity of its effects on climate change, there is an increasing demand to generate biofuels to replace petroleum-based gasoline. While most investigations have centered on fatty acid synthases, the versatility of polyketide synthases (PKSs) could establish a new biosynthetic platform for biofuel production. As b-carbonyl reduction is a fundamental component of PKS flexibility, we seek to further explore the design principles in reductive loop exchanges to produce fully reduced carboxylic acids. We accomplished this by introducing heterologous fully reductive domains from various PKS clusters into the first extension module of lipomycin, which programmatically should produce a fully reduced carboxylic acid when fused with a heterologous thioesterase. We generated a library of plasmids with chimeric modules containing a fully reducing domain from PKSs with varying acyltransferase selectivity and substrate size. Production of carboxylic acids was tested in vivo through the heterologous expression of the plasmid library in Streptomyces albus. As successful production was reliant on matching the module’s native AT selectivity and substrate size, we hypothesized that these two factors are critical design principles. To further test this hypothesis, we identified two more fully reductive loops through the software ClusterCad that match these parameters. Collectively, our work strengthens the scientific literature regarding reductive loop swaps and moves the field closer to the production of “designer” biofuels.