An update on the review of microbial synthesis of glucosamine and N-acetylglucosamine.

Glucosamine (GlcN) is a natural amino monosaccharide in which a hydroxyl group of glucose is substituted by an amino group. It belongs to functional amino sugar compounds. In the traditional preparation process, GlcN and GlcNAc are obtained by hydrolyzing the cell wall of shrimp and crab. There are many potential problems with this method, such as geographical and seasonal restrictions on the supply of raw materials, serious environmental pollution and potential allergic reactions. Microbial fermentation has the advantages of mild conditions, low environmental pollution, high production intensity, and product safety. It can effectively solve the problem of shrimp and crab hydrolysis process, attracting many researchers to participate in the research of microbial fermentation production of GlcN. This paper mainly summarizes the research on strain construction method, metabolic pathway design and fermentation condition optimization in microbial fermentation, which has certain guiding significance for the further production, research and production of glucosamine.

A review on microbial synthesis of lactate-containing polyesters.

Degradable polylactic acids (PLA) have been widely used in agriculture, textile, medicine and degradable plastics industry, and can completely replace petroleum-based plastics in the future. At present, polylactic acid was chemically synthesized by ring-opening polymerisation or the direct polycondensation of lactic acid, which inevitably leads to chemical and heavy metal catalyst pollution. The current research focus has gradually shifted to the development of recombinant industrial strains for the efficiently production of lactate-containing polyesters from renewable resources. This review summarizes various explorations of metabolic pathway optimization and production cost control in the industrialization of lactate-containing polyesters bio-production. In particular, the effects of key enzymes, including CoA transferase, polyhydroxyalkanoate synthase, and their mutants, culture conditions, low-cost carbon sources, and recombinant strains on the yield and composition of lactate-containing polyesters are summarized and discussed. Future prospects and challenges for the industrialization of lactate-containing polyesters are also pointed out.

An acetate-independent pathway for isopropanol production via HMG-CoA in Escherichia coli.

Isopropanol has a good potential as a new fuel substitution. In the model biosynthesis pathway of isopropanol synthesis, acetoacetyl-CoA is converted to acetoacetate by acetoacetyl-CoA transferases, which requires an acetate molecule as a substrate. Herein, a novel isopropanol synthesis pathway based on mammalian ketone metabolic pathway was developed. In this pathway, acetoacetyl-CoA is condensed with acetyl-CoA to generate 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) by HMG-CoA synthase, and then catalyzed by HMG-CoA lyase to generate acetoacetate. This process is acetate-independent. Under the same experimental system using glycerol as carbon source, the E. coli strain MG::ISOP1 containing the novel pathway produced 11.7 times more isopropanol than the strain MG::ISOP0 containing the model pathway. The pta-ackA knockout mutant strain MG∆pta-ackA::ISOP1, which reduced the conversion of acetyl-CoA to acetate, further increased the production from 76 mg/L to 360 mg/L. In another strategy, knocking out atoDA to block the acetoacetate degradation pathway in strain MG∆atoDA::ISOP1 increased the production to 680 mg/L. By knocking out both of pta-ackA and atoDA, strain MGΔpta-ackAΔatoDA::ISOP1 produced 964 mg/L of isopropanol, which was 12.7 times that of MG::ISOP1. This study indicated that the novel pathway is competent for isopropanol synthesis, and provides a new perspective for biosynthesis of isopropanol.