Recent technological and strategical developments in the biomanufacturing of 1,3-propanediol from glycerol

In the pursuit of sustainable development, there is a rapid increase in the generation of biodiesel, which eventually results in the synthesis of glycerol as a major by-product. The surplus amount of glycerol from biodiesel industries is one of the rising environmental concerns. Alternatively, glycerol can serve as an attractive raw material for synthesizing value-added products that offer simultaneous management and valorization of this waste. 1,3-propanediol is a vital value-added material having extensive applications in the industrial domain. Microbial biosynthesis of 1,3-propanediol from glycerol has proven to be an economic and eco-friendly approach. However, biosynthesis of this bio-product is often affected by some environmental stresses, such as glycerol and 1,3-propanediol concentrations, accumulation of 3-hydroxypropionaldehyde, and by-product synthesis. To overcome the influences of these factors as well as to improve 1,3-propanediol yield, efforts have been devoted over the past years, which mostly included the application of metabolic engineering strategies to transform microbial strains into robust cell factories. This review focuses on the environmental stresses restricting 1,3-propanediol biosynthesis, and how these restrictions could be overcome using the metabolic engineering strategies. In this context, some technological and strategical aspects, including rechanneling metabolic flux in co-producing strains, rebalancing of co-factors and gene expression, co-culture and co-substrate fermentation, and application of untranslated region engineering. It also discusses the role of key enzymes involved in 1,3-propanediol biosynthesis and the influence of polyhydroxyalkanoate granule-associated protein on the tolerance to high concentration of this bio-product.