A Kinetic Framework for Modeling Oleochemical Biosynthesis in E. coli
Abstract
Microorganisms build fatty acids with biocatalytic assembly lines, or
fatty acid synthases (FASs), that can be repurposed to produce a broad
set of fuels and chemicals. Despite their versatility, the product
profiles of FAS-based pathways are challenging to adjust without
experimental iteration, and off-target products are common. This study
uses a detailed kinetic model of the E. coli FAS as a foundation
to model nine oleochemical pathways. These models provide good fits to
experimental data and help explain unexpected results from in
vivo studies. An analysis of pathways for alkanes and fatty acid ethyl
esters, for example, suggests that reductions in titer caused by enzyme
overexpression can result from shifts in pools of metabolic
intermediates that are incompatible with the substrate specificities of
downstream enzymes. In general, different engineering objectives (i.e.,
production, unsaturated fraction, and average chain length) show
experimentally consistent sensitivities to pathway enzymes, and
model-based compositional analyses indicate simple shifts in enzyme
concentrations can alter the product profiles of pathways with
promiscuous components. The study concludes by integrating all models
into a graphical user interface. The models supplied by this work
provide a versatile kinetic framework for studying oleochemical pathways
in different biochemical contexts.