Metabolic engineering of 1,3-propanediol synthesis in Citrobacter freundii CF-5

Abstract:

[Objective] The metabolism of 1,3-propanediol in Citrobacter freundii was studied. [Methods] Transcriptional fusion reporter genes of GSR-lacZ, PDO-lacZ, and GL-lacZ were constructed. Based on this, the mariner transposon libraries were constructed. [Results] Six mutants were isolated. The expression level of the corresponding key enzymes was increased from 1 to 11 folds in the mutants, and the corresponding 1,3-propanediol production was increased from 3% to 50%. Transposon insertion sites were analyzed and the results show that the β-lactamase gene was inactivated in 5 mutants and the dihydrolipoamide acyltransferase gene was inactivated in 1 mutant. Furthermore, the expression levels of glycerol dehydrogenase and glycerol dehydratase were increased significantly in the β-lactamase mutant, whereas no increase of the 1,3-propanediol oxidoreductase expression was observed. In the diydrolipoamide acyltransferase mutant, 1,3-propanediol oxidoreductase expression level was significantly improved, whereas the other two enzymes expression level remained unchanged. [Conclusion] The results provide insight into constructing engineering strains producing a high level of 1,3-propanediol.