# Metabolic engineering enables Escherichia coli to grow on 1,3-propanediol

## TL;DR

Scientists engineered E. coli to grow on 1,3-propanediol, a chemical from plastics, which could help recycle plastic waste.

## Contribution

A new E. coli strain (PA16) was developed to efficiently consume 1,3-propanediol using metabolic pathway extensions and gene overexpression.

## Key findings

- PA16 reached an OD600 of 7 by consuming 6.5 g/L of 1,3-PDO in 72 hours.
- Overexpression of EcTdh and EcKbl genes improved cell density by 5-fold.
- The growth medium was simplified to include only 0.1 g/L threonine and 10 g/L 1,3-PDO.

## Abstract

1,3-propanediol (1,3-PDO) is used to synthesize plastics used in many consumer products. As the demand and production of such plastics increase, a technology will be needed to utilize 1,3-PDO released from the plastics after their disposal. In our previous study, we developed the strain (BA07Δ) that could use malonate semialdehyde (MSA, an important intermediate in the 1,3-PDO assimilation pathway) as the major carbon source. Here, we present construction of PA16, a strain which could grow to an OD600 of 7 by consuming 6.5 g/L of 1,3-PDO within 72 h in M9-based medium supplemented with 1 g/L of complete supplement mixture (CSM). This was achieved by adaptive laboratory evolution (ALE) after extending the pathway in BA07Δ through the introduction of a 1,3-propanediol dehydrogenase from Klebsiella pneumoniae (KpDhaT), an aldehyde dehydrogenase from E. coli (EcPuuC) and a 3-hydroxypropionate dehydrogenase from Halomonas bluephagenesis (HbDddA). Comparing the transcriptome of PA16 and its ancestor in the ALE (PA1) revealed the upregulation of two genes, threonine dehydrogenase (EcTdh) and 2-amino-3-ketobutyrate CoA ligase (EcKbl) responsible for threonine degradation. The overexpression of these genes in PA1 resulted in a 5-fold increase in the 72-h cell density. This finding helped simplify the growth medium of PA16: the supplement mixture containing more than 10 amino acids/nucleobases was reduced to just having 0.1 g/L threonine. PA16's OD600 reached 3 when it grew in a defined medium containing 10 g/L 1,3-PDO and 0.1 g/L threonine as carbon sources. E. coliPA16 should be a useful strain to the subsequent research on upcycling 1,3-PDO derived from plastic wastes.

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