Recent advances in the microbial production of C4 alcohols by metabolically engineered microorganisms.

BACKGROUND: The heavy global dependence on petroleum-based industries has led to serious environmental problems, including climate change and global warming. As a result, there have been calls for a paradigm shift towards the use of biorefineries, which employ natural and engineered microorganisms that can utilize various carbon sources from renewable resources as host strains for the carbon-neutral production of target products. PURPOSE AND SCOPE: C4 alcohols are versatile chemicals that can be used directly as biofuels and bulk chemicals and in the production of value-added materials such as plastics, cosmetics, and pharmaceuticals. C4 alcohols can be effectively produced by microorganisms using DCEO biotechnology (tools to design, construct, evaluate, and optimize) and metabolic engineering strategies. SUMMARY OF NEW SYNTHESIS AND CONCLUSIONS: In this review, we summarize the production strategies and various synthetic tools available for the production of C4 alcohols and discuss the potential development of microbial cell factories, including the optimization of fermentation processes, that offer cost competitiveness and potential industrial commercialization.

Recent Advances in Sustainable Plastic Upcycling and Biopolymers.

Advances in scientific technology in the early twentieth century have facilitated the development of synthetic plastics that are lightweight, rigid, and can be easily molded into a desirable shape without changing their material properties. Thus, plastics become ubiquitous and indispensable materials that are used in various manufacturing sectors, including clothing, automotive, medical, and electronic industries. However, strong physical durability and chemical stability of synthetic plastics, most of which are produced from fossil fuels, hinder their complete degradation when they are improperly discarded after use. In addition, accumulated plastic wastes without degradation have caused severe environmental problems, such as microplastics pollution and plastic islands. Thus, the usage and production of plastics is not free from environmental pollution or resource depletion. In order to lessen the impact of climate change and reduce plastic pollution, it is necessary to understand and address the current plastic life cycles. In this review, "sustainable biopolymers" are suggested as a promising solution to the current plastic crisis. The desired properties of sustainable biopolymers and bio-based and bio/chemical hybrid technologies for the development of sustainable biopolymers are mainly discussed.

Metabolic engineering for the synthesis of polyesters: A 100-year journey from polyhydroxyalkanoates to non-natural microbial polyesters.

As concerns increase regarding sustainable industries and environmental pollutions caused by the accumulation of non-degradable plastic wastes, bio-based polymers, particularly biodegradable plastics, have attracted considerable attention as potential candidates for solving these problems by substituting petroleum-based plastics. Among these candidates, polyhydroxyalkanoates (PHAs), natural polyesters that are synthesized and accumulated in a range of microorganisms, are considered as promising biopolymers since they have biocompatibility, biodegradability, and material properties similar to those of commodity plastics. Accordingly, substantial efforts have been made to gain a better understanding of mechanisms related to the biosynthesis and properties of PHAs and to develop natural and recombinant microorganisms that can efficiently produce PHAs comprising desired monomers with high titer and productivity for industrial applications. Recent advances in biotechnology, including those related to evolutionary engineering, synthetic biology, and systems biology, can provide efficient and effective tools and strategies that reduce time, labor, and costs to develop microbial platform strains that produce desired chemicals and materials. Adopting these technologies in a systematic manner has enabled microbial fermentative production of non-natural polyesters such as poly(lactate) [PLA], poly(lactate-co-glycolate) [PLGA], and even polyesters consisting of aromatic monomers from renewable biomass-derived carbohydrates, which can be widely used in current chemical industries. In this review, we present an overview of strain development for the production of various important natural PHAs, which will give the reader an insight into the recent advances and provide indicators for the future direction of engineering microorganisms as plastic cell factories. On the basis of our current understanding of PHA biosynthesis systems, we discuss recent advances in the approaches adopted for strain development in the production of non-natural polyesters, notably 2-hydroxycarboxylic acid-containing polymers, with particular reference to systems metabolic engineering strategies.