1 | INTRODUCTION
Microorganisms can produce a diverse set of oleochemicals from renewable
feedstocks and are centrally important to the emerging green bioeconomy
(Akinsemolu, 2018; Kumar and Kumar, 2017). Microbially produced
alcohols, esters, olefines, alkanes, ketones, and polyesters are
promising transportation fuels (Bao et al., 2016; Choi and Lee, 2013;
Teo et al., 2015), herbicides (Kim et al., 2015), lubricants (Rui et
al., 2015), flavors (Lian and Zhao, 2015), fragrances (Goh et al., 2012;
Sherkhanov et al., 2016), and polymer additives (Bowen et al., 2016;
Clomburg et al., 2015). In engineered microbes, oleochemical
biosynthesis typically begins with a fatty acid synthase (FAS), which
builds acyl-ACPs of varying lengths, and concludes with the enzymatic
conversion of acyl-ACPs to target products ((Sarria et al., 2017; White
et al., 2005); Fig. 1). Despite the versatility of FAS-based systems,
their activities are challenging to tune—a reflection of their
sensitivity to the concentrations, kinetics, and substrate specificities
of multiple enzymes (Mains et al., 2022; Ruppe and Fox, 2018; Tan et
al., 2018; Xu et al., 2013). This challenge is illustrated by ongoing
efforts to engineer oleochemical pathways with well-defined product
profiles (Blitzblau et al., 2021; Haushalter et al., 2014; Hernández
Lozada et al., 2018; Hernández Lozada et al., 2020); pathway
optimization typically requires iteration, and off-target products are
common (Grisewood et al., 2017; Sarria et al., 2018).
Mathematical models can facilitate the systematic analysis of cellular
metabolism and have guided the design of oleochemical-producing strains.
Genome-scale models use the stoichiometries of metabolic networks to
predict flux under different growth conditions (Machado and Herrgård,
2015; Zhang and Hua, 2016); when paired with flux balance analysis
(FBA), they can reveal genetic adjustments (e.g., gene deletion) likely
to re-route flux toward specific products (Agren et al., 2013; Ravi and
Gunawan, 2021; Yoshikawa et al., 2017).