Metabolic engineering of a newly isolated Citrobacter braakii strain to produce 1,3-propanediol from glycerol

Abstract

In this study, a promising bacterial strain for the bio-production of 1,3-propandeiol was isolated as a contaminant from a pilot-scale ethanol-producing bioreactor that used glycerol as a substrate. The isolated strain was identified as Citrobacter braakii and named TB-96. As TB-96 showed a fast growth rate, had strong antibiotic resistance, and could assimilate glycerol to produce high concentrations of 1,3-propanediol, it was used for further investigation to promote the biorefining of waste glycerol generated from biodiesel fuel production. First, to increase the 1,3-propanediol productivity of TB-96, the whole genome was sequenced, and the metabolic pathways were investigated. Next, the synthesis pathways of the main by-products—lactate and formate—were disrupted to construct the strain TB-96-dLF. In fed-batch experiments, TB-96-dLF produced up to 60 g/L 1,3-propanediol using only corn steep liquor as a low-cost nitrogen source.