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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.

Bacterial cellulose (BC) is widely used in the food industry for products such as nata de coco. The mechanical properties of BC hydrogels, including stiffness and viscoelasticity, are determined by the hydrated fibril network. Generally, Komagataeibacter bacteria produce gluconic acids in a glucose medium, which may affect the pH, structure and mechanical properties of BC. In this work, the effect of pH buffer on the yields of Komagataeibacter hansenii strain ATCC 53582 was studied. The bacterium in a phosphate and phthalate buffer with low ionic strength produced a good BC yield (5.16 and 4.63 g/l respectively), but there was a substantial reduction in pH due to the accumulation of gluconic acid. However, the addition of gluconic acid enhanced the polymer density and mechanical properties of BC hydrogels. The effect was similar to that of the bacteria using glycerol in another carbon metabolism circuit, which provided good pH stability and a higher conversion rate of carbon. This study may broaden the understanding of how carbon sources affect BC biosynthesis.

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