Biotechnological conversion of glycerol from biofuels to 1,3-propanediol using Escherichia coli

In the face of shortage of fossil fuel supplies and climate warming triggered by excessive carbon dioxide emission, alternative resources for chemical industry have gained considerable attention. Renewable resources and their derivatives are of particular interest. Glycerol, which constitutes one of the by-products during biodiesel production, is such a substrate. Thus, generated excess glycerol may become an environmental problem, since it cannot be disposed of in the environment. The most promising products obtained from glycerol are polyols, including 1,3-propanediol, an important substrate in the production of synthetic materials, e.g. polyurethanes, unsaturated polyesters, and epoxy resins. Glycerol can be used as a carbon and energy source for microbial growth in industrial microbiology to produce 1,3-propanediol. This paper is a review of metabolic pathways of native producers and E. coli with the acquired ability to produce the diol via genetic manipulations. Culture conditions during 1,3-PDO production and genetic modifications of E. coli used in order to increase efficiency of glycerol bioconversion are also described in this paper

1,3-Propanediol production by Escherichia coli using genes from Citrobacter freundii atcc 8090

Compared with chemical synthesis, fermentation has the advantage of mass production at low cost, and has been used in the production of various industrial chemicals. As a valuable organic compound, 1,3-propanediol (1,3-PDO) has numerous applications in the production of polymers, lubricants, cosmetics and medicines. Here, conversion of glycerol (a renewable substrate and waste from biodiesel production) to 1,3-PDO by E. coli bacterial strain carrying altered glycerol metabolic pathway was investigated. Two gene constructs containing the 1,3-PDO operon from Citrobacter freundii (pCF1 and pCF2) were used to transform the bacteria. The pCF1 gene expression construct contained dhaBCE genes encoding the three subunits of glycerol dehydratase, dhaF encoding the large subunit of the glycerol dehydratase reactivation factor and dhaG encoding the small subunit of the glycerol dehydratase reactivating factor. The pCF2 gene expression construct contained the dhaT gene encoding the 1,3-propanediol dehydrogenase. Expression of the genes cloned in the above constructs was under regulation of the T7lac promoter. RT-PCR, SDS-PAGE analyses and functional tests confirmed that 1,3-PDO synthesis pathway genes were expressed at the RNA and protein levels, and worked flawlessly in the heterologous host. In a batch flask culture, in a short time applied just to identify the 1,3-PDO in a preliminary study, the recombinant E. coli bacteria produced 1.53 g/L of 1,3-PDO, using 21.2 g/L of glycerol in 72 h. In the Sartorius Biostat B Plus reactor, they produced 11.7 g/L of 1,3-PDO using 24.2 g/L of glycerol, attaining an efficiency of 0.58 [mol1,3-PDO/molglycerol]