Indole-3-acetic acid (IAA) is a critical plant hormone that regulates cell division, development, and metabolism. IAA synthesis in plants and plant-associated microorganisms cannot fulfill the requirement for large-scale agricultural production. Here, two novel IAA biosynthesis pathways, tryptamine (TAM) and indole-3-acetamide (IAM), were developed for IAA production by whole-cell catalysis and de novo biosynthesis in an engineered Escherichia coli MG1655. When 10 g/L L-tryptophan was used as a substrate, an MIA-6 strain containing a heterologous IAM pathway had the highest IAA titer of 7.10 g/L (1.34 × 10 3 mg/g DCW), which was 98.4 times more than MTAI-5 containing the TAM pathway by whole-cell catalysis. De novo IAA biosynthesis was optimized by improving NAD(P)H availability, resulting in an increased IAA titer of 906 mg/L obtained by the MGΔadhE::icd strain, which is 29.7% higher than the control. These strategies exhibit the potential for IAA production in engineered E. coli and possible industrial applications.

Coenzyme Q10 (CoQ10)—an essential cofactor in the respiratory electron transport chain—has important pharmaceutical and healthcare applications. Farnesol (FOH)—an acyclic sesquiterpene alcohol—has garnered interest owing to its valuable clinical and medical benefits. Here, the coproduction of CoQ10 and FOH in Rhodobacter sphaeroides GY-2 was greatly improved through the enhancement of intracellular NADPH availability. Transcription of pgi, gdhA, and nuocd was, respectively, inhibited using RNA interference to reduce intracellular NAD(P)H consumption. Moreover, zwf, gnd, and zwf + gnd were overexpressed to enhance the pentose phosphate pathway, resulting in improved NADPH availability in most metabolically engineered R. sphaeroides strains. RSg-pgi with RNAi of pgi combined with overexpression of gnd produced 55.05 mg/L FOH that is twofold higher than the parental strain GY-2, and 185.5 mg/L CoQ10 can be coproduced at the same time. In conclusion, improved carbon flux can be redirected toward NADPH-dependent biosynthesis through the enhancement of NADPH availability.

Serotonin is a neurotransmitter that plays an essential regulatory role in numerous cognitive and behavioral functions. Recent advances in synthetic biology have enabled engineering of non-natural biosynthetic pathways for serotonin production in E. coli. Here, an optimized heterologous serotonin biosynthetic pathway was engineered in E. coli and coupled with the biosynthetic and regeneration modules of the endogenous vital cofactor tetrahydrobiopterin (BH4) for efficient serotonin production using whole-cell catalysis. Further metabolic engineering efforts were performed to ensure an adequate endogenous BH4 supply, including enhancements of GTP biosynthesis and intracellular reducing power availability. Using the optimized fed-batch fermentation, an overall maximum serotonin yield of 40.3% (mol/mol) and a peak titer of 1.68 g/L (production rate of 0.016 g/L/h) were achieved. The strategies employed in this study show the promise of using E. coli for pterin self-sufficiency and high-level serotonin production, and the engineered strains hold the potential for use in industrial applications.