Terpenes are an important class of natural secondary metabolites with a wide range of applications in food, pharmaceuticals, and biofuels. Currently, the traditional production methods of terpenes almost depend on plant extraction and chemical conversion. The plant extraction method consumes a lot of natural resources and makes it difficult to separate the target compound from the extractives, while the chemical conversion method has a complex synthesis route and leads to severe environmental pollution. Compared to plant extraction and chemical conversion methods, the microbial synthesis method has the advantages of preferable sustainability, low production cost and environmental friendliness, and is a potential way to achieve efficient terpenes production in the future. Yeast is a conventional platform for bio-chemical production and is also engineered to synthesize terpenes due to their abundant intracellular acetyl-CoA, high metabolic flux of the MVA pathway, high local concentrations of substrates and enzymes, and fewer by-products. At present, a variety of terpenes including α-farnesene, squalene, limonene, β-carotene have been successfully synthesized by the engineered yeast via the application of multiple strategies. This work summarized the progress of research on these strategies conducted in the synthesis of terpenes from several aspects, including the adaptive screening and expression of terpene synthases, the regulation of synthesis pathways, and the application of intracellular compartmentalized expression strategy. The perspectives and challenges were also discussed, from which it was hoped that some useful views for future research on the synthesis of terpenes in yeast would be provided.

Itaconic acid (ITA) is one of the top 12 platform chemicals. The global ITA market is expanding due to the rising demand for bio-based unsaturated polyester resin and its non-toxic qualities. Although bioconversion using microbes is the main approach in the current industrial production of ITA, ecological production of bio-based ITA faces several issues due to: low production efficiency, the difficulty to employ inexpensive raw materials, and high manufacturing costs. As metabolic engineering advances, the engineering of microorganisms offers a novel strategy for the promotion of ITA bio-production. In this review, the most recent developments in the production of ITA through fermentation and metabolic engineering are compiled from a variety of perspectives, including the identification of the ITA synthesis pathway, the metabolic engineering of natural ITA producers, the design and construction of the ITA synthesis pathway in model chassis, and the creation, as well as application, of new metabolic engineering strategies in ITA production. The challenges encountered in the bio-production of ITA in microbial cell factories are discussed, and some suggestions for future study are also proposed, which it is hoped offers insightful views to promote the cost-efficient and sustainable industrial production of ITA.

Adipic acid is an important bulk chemical used in the nylon industry, as well as in food, plasticizers and pharmaceutical fields. It is thus considered one of the most important 12 platform chemicals. The current production of adipic acid relies on non-renewable petrochemical resources and emits large amounts of greenhouse gases. The bio-production of adipic acid from renewable resources via engineered microorganisms is regarded as a green and potential method to replace chemical conversion, and has attracted attention all over the world. Herein we review the current status of research on several artificial pathways for the biosynthesis of adipic acid, especially the reverse degradation pathway, which is a full biosynthetic method and has achieved the highest titer of adipic acid so far. Other artificial pathways including the fatty acid degradation pathway, the muconic acid conversion pathway, the polyketide pathway, the α-ketopimelate pathway and the lysine degradation pathway are also discussed. In addition, the challenges in the bio-production of adipic acid via these artificial pathways are analyzed and the prospects are presented with the intention of providing some significant points for the promotion of adipic acid biosynthesis.