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6-Aminocaproic acid (6ACA) and 1,6-hexamethylenediamine (HMDA) are key precursors for nylon synthesis, and both are produced using petroleum-based chemical processes. However, the utilization of bio-based raw materials for biological production of monomers is crucial for nylon industry. In this study, we demonstrated that metabolic engineering of Escherichia coli and selected mutations of α-keto acid decarboxylase successfully synthesized 6ACA and HMDA. An artificial iterative cycle from l-lysine to chain-extended α-ketoacids was introduced into Escherichia coli BL21 (DE3). Then, the extended α-ketoacids were decarboxylated and oxidized for 6ACA production. Overexpression of catalase (KatE) combined with the site-directed mutations of α-isopropylmalate synthase (LeuA) contributed synergistic enhancement effect on synthesis of 6ACA, resulting in a 1.3-fold increase in 6ACA titer. Selected mutations in α-keto acid decarboxylase (KivD) improved its specificity and 170.00 ± 5.57 mg/L of 6ACA with a yield of 0.13 mol/mol (6ACA/l-lysine hydrochloride) was achieved by shake flask cultivation of the engineered strain with the KivD# (F381Y/V461I). Meanwhile, the engineered E. coli could accumulate 84.67 ± 4.04 mg/L of HMDA with a yield of 0.08 mol/mol (HMDA/l-lysine hydrochloride) by replacing aldehyde dehydrogenase with bi-aminotransferases. This achievement marks a significant advancement in the biological synthesis of 6-carbon compounds, since the biosynthetic pathways of HMDA are rarely identified., (© 2024 Wiley Periodicals LLC.)

As an important five-carbon platform chemical to synthesize polyesters and polyamides, glutaric acid is widely used in numerous biochemical fields such as consumer goods, textile, and footwear industries. However, the application of glutaric acid is limited by the low yield of its bio-production. In this study, a metabolically engineered Escherichia coli LQ-1 based on 5-aminovalerate (AMV) pathway was used for glutaric acid fed-batch fermentation. Given the significance of nitrogen source in the bio-production of glutaric acid by AMV pathway, a novel nitrogen source feeding strategy feedbacked by real-time physiological parameters was proposed after evaluating the effects of nitrogen source feeding (such as ammonia and ammonium sulfate) on glutaric acid bio-production. Under the proposed nitrogen source feeding strategy, a significantly improved glutaric acid production of 53.7 g L -1 was achieved in a 30 L fed-batch fermentation by the metabolically engineered E. coli LQ-1, which was an improvement of 52.1% over pre-optimization. Additionally, a higher conversion rate of 0.64 mol mol -1 (glutaric acid/glucose) was obtained compared with the previously reported bio-production of glutaric acid with E. coli. These results indicated that the nitrogen source feeding strategy proposed in this study will be useful for achieving the efficient and sustainable bio-based production of glutaric acid., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

There is increasing industrial demand for five-carbon platform chemicals, particularly 5-hydroxyvaleric acid (5-HV), a widely used building block for the synthesis of polyesters and polyurethanes. Here, we developed an efficient 5-HV microbial producer by systems metabolic engineering of Escherichia coli W3110. To derive 5-HV, Pseudomonas putida l -lysine monooxygenase (davB) and 5-aminovaleramide amidohydrolase (davA), E. coli 4-aminobutyrate aminotransferase (gabT), and different aldehyde reductase genes were introduced to E. coli W3110 to convert l -lysine hydrochloride to the target product. Three aldehyde reductases, including YajO from P. putida and YahK and YqhD from E. coli, were examined, revealing that the overexpression of aldehyde reductases was critical for 5-HV production and YajO was first reported for efficient production of 5-HV. The E. coli 5-aminovalerate exporter encoded by gabP and E. coli lysine-specific permease encoded by lysP were expressed to further enhance 5-HV production. In addition, a hok/sok toxin/antitoxin system based on the E. coli XL1-Blue genome was inserted to the dual-vector system to decrease plasmid loss. Finally, 5.59 g/L of 5-HV with a yield of 0.96 mol/mol (5-HV/ l -lysine hydrochloride) by shake flask cultivation of the engineered E. coli W3110 and 35.6 g/L of 5-HV with a yield of 0.92 mol/mol (5-HV/ l -lysine hydrochloride) by fed fermentation were achieved respectively. The developed metabolic engineering strategies provide a basis for the efficient and sustainable bio-based production of 5-HV. [Display omitted] • YajO is a novel and effective aldehyde reductase for 5-hydroxyvaleric acid production. • GabP and LysP improved 5-hydroxyvaleric acid production to 2.73 g/L. • The hok/sok system improved 5-hydroxyvaleric acid production to 5.59 g/L. • 35.6 g/L of 5-hydroxyvaleric acid was achieved by batch fermentation. [ABSTRACT FROM AUTHOR]

With the increasing attention to environmental issues and sustainable development, bio-production of diamines from renewable raw materials is very important for the establishment of a sustainable nylon industry. A three carbon linear chain diamine, 1,3-diaminopropane (1,3-DAP), is an important platform chemical and has the potential for novel types of polyamides preparation. In this study, the C 4 biosynthetic pathway for 1,3-DAP reported before was introduced into Escherichia coli W3110 and homolog mining of 2-ketoglutarate 4-aminotransferase genes was conducted to increase 1,3-DAP production. We demonstrated that aminotransferase RocD from Bacillus subtilis 168 was the most effective one among the candidates. Meanwhile, l -aspartate transporters such as GltP from E. coli, GltP and GltT from B. subtilis 168 were examined to further improve the 1,3-DAP production. Subsequently, the dual-vector systems were introduced to the host to co-express aminotransferases from different sources and the engineered E. coli W3110 could accumulate 302 mg/L of 1,3-DAP with a yield of 0.31 mol/mol (1,3-DAP/ l -aspartate) on the shake flask cultivation. The strategies reported here will be useful for the efficient and sustainable bio-based production of 1,3-DAP. • Aminotransferase RocD was first used for efficient production of 1,3-diaminopropane. • l -aspartate transporter GltTbsu improved 1, 3-diaminopropane production by 23.03 %. • Two-aminotransferase system increased 1, 3-diaminopropane titer to 302 mg/L. [ABSTRACT FROM AUTHOR]