Efficient 3‐Hydroxybutyrate Production by Quiescent Escherichia coli Microbial Cell Factories is Facilitated by Indole‐Induced Proteomic and Metabolomic Changes

11 Jun 2018

The authors show that quiescent (Q‐Cell) Escherichia coli cultures can maintain metabolic activity in the absence of growth for up to 24 h, leading to four times greater specific productivity of a model metabolite, 3‐hydroxybutyrate (3HB), than a control. Q‐cells can be created by using the proton ionophore indole to halt cell division of an hns mutant strain. This uncouples metabolism from cell growth and allows for more efficient use of carbon feedstocks because less metabolic effort is diverted to surplus biomass production. However, the reason for the increased productivity of cells in the quiescent state was previously unknown. In this study, proteome expression patterns between wild‐type and Q‐cell cultures show that Q‐cells overexpress stress response proteins, which prime them to tolerate the metabolic imbalances incurred through indole addition. Metabolomic data reveal the accumulation of acetyl‐coenzyme A and phosphoenolpyruvate: excellent starting points for high‐value chemical production. We demonstrate the exploitation of these accumulated metabolites by engineering a simple pathway for 3HB production from acetyl‐coenzyme A. Quiescent cultures produced half the cell biomass of control cultures lacking indole, but were still able to produce 39.4 g L−1 of 3HB compared to 18.6 g L−1 in the control. Q‐cells therefore have great potential as a platform technology for the efficient production of a wide range of commodity and high value chemicals.