One of our research interests in our group is the designing artificial biocatalytic cascade, as an alternative to traditional chemical process, for the synthesis of functional chemicals. Some elegant examples have been achieved in our previous study, such as converting cyclohexane into all three enantiomers of cyclohexane-1,2-diols as building blocks for pharmaceutical synthesis,¹ as well as cascade biotransformation of benzene into arbutin possessing anti-oxidant, anti-inflammatory and antibacterial activities.²

    In current study, biosynthesis of aliphatic α,ω-Dicarboxylic acids (DCAs) was targeted since DCAs have very important industrial application in the preparation of perfumes, polymers, adhesives, etc. In addition, we realized that the majority of industrial DCAs are currently produced by energy-intensive, multistage chemical oxidations that are hazardous to the environment. One of the most industrially important DCAs ——adipic acid, for instance, this process generates almost 10% of global anthropogenic nitrous oxide N₂O emissions due to the use of a large amount of nitric acid, which contributes to global warming and ozone depletion. Therefore, the development of environmentally friendly, safe, neutral routes to DCAs is an urgent issue.

Figure 1

    To achieve the goal, we designed an in vivo artificially biocatalytic cascade for oxidation of cycloalkanes to DCAs in the form of microbial consortium, composed of three cell modules (Figure 1).³ The developed biocatalytic system has the following advantages: (i) protein expression burden and redox constraints can be reduced by distributing the biocatalytic pathway among different cell modules; (ii) each expression system or cell module can be constructed and optimized in parallel, substantially reducing development time; and (iii) the catalyst loading of each cell module can be adjusted, allowing beneficial interactions among cell modules to enhance productivity. Consequently, the designed consortia of E. coli containing the modules efficiently converted cycloalkanes to DCAs with only oxygen and water under mild conditions.

    In summary, the biocatalytic process we developed is an ideal solution to the problems encountered in the industrial chemical processes for synthesis of DCAs from cycloalkanes. The easier product isolation and substrate recovery procedure of our approach shows great advantages over chemical and fermentation methods. The concept of microbial-consortia-mediated biocatalytic pathway reconstruction and redox self-sufficiency-based modularization provides solutions and guidance for further development of in vivo artificial biocatalytic cascades for challenging transformations.

1. Aitao Li, Adriana Ilie, Zhoutong Sun, Richard Lonsdale, Jian-He Xu, Manfred T. Reetz*. Whole-Cell-Catalyzed Multiple Regio- and Stereoselective Functionalizations in Cascade Reactions Enabled by Directed Evolution. Angew. Chem. Int. Ed. 2016, 128,12205-12208.
2. Hangyu Zhou^#, Binju Wang^#, Fei Wang, Xiaojuan Yu, Lixin Ma, Aitao Li*, Manfred T. Reetz*. Chemo- and Regioselective Dihydroxylation of Benzene to Hydroquinone Enabled by Engineered Cytochrome P450 Monooxygenase. Angew. Chem. Int. Ed. 2019, 58, 764–768.
3. Fei Wang^#, Jing Zhao^#, Qian Li^#, Jun Yang, Renjie Li, Jian Min, Xiaojuan Yu, Gao-Wei Zheng, Hui-Lei Yu, Chao Zhai, Carlos G. Acevedo-Rocha, Lixin Ma, Aitao Li*. One-pot biocatalytic route from cycloalkanes to α, ω‐dicarboxylic acids by designed Escherichia coli consortia. Nature communications, 2020, 11, 5035.