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

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 (<b>BA07Δ</b>) 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 <b>PA16</b>, 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 <b>BA07Δ</b> through the introduction of a 1,3-propanediol dehydrogenase from <i>Klebsiella pneumoniae</i> (KpDhaT), an aldehyde dehydrogenase from <i>E. coli</i> (EcPuuC) and a 3-hydroxypropionate dehydrogenase from <i>Halomonas bluephagenesis</i> (HbDddA). Comparing the transcriptome of <b>PA16</b> and its ancestor in the ALE (<b>PA1</b>) 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 <b>PA1</b> resulted in a 5-fold increase in the 72-h cell density. This finding helped simplify the growth medium of <b>PA16</b>: the supplement mixture containing more than 10 amino acids/nucleobases was reduced to just having 0.1 g/L threonine. <b>PA16</b>'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. <i>E. coli</i> <b>PA16</b> should be a useful strain to the subsequent research on upcycling 1,3-PDO derived from plastic wastes.