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).