Metabolic Engineering for the Production of Diols

During recent years, the reduced use of chemical processes to produce commodity chemicals, and their substitution with microbiological alternatives, has been frequently observed. However, because of the low efficiency of these biotechnological synthetic materials, investigations are constantly being performed to increase their productivity by controlling the metabolism of bacterial cells. One solution to this problem would be to modify the environmental conditions of the culture of microorganisms or, alternatively, to control the composition of the culture medium by using additional and important enzymes that serve as cofactors in metabolite production. Such production by microorganisms can be also improved by employing genetic engineering tools, whereby modified bacteria are able to synthesize several-fold more desirable metabolites than can wild-type strains. The biotechnological synthesis of diols such as 1,2-propanediol (1,2-PD), 1,3-propanediol (1,3-PD) and 2,3-butanediol (2,3-BD) by the direct microbial bioconversion of renewable feedstocks, and even from waste materials of biofuel production, has been well described. These diols are widely used in many branches of industry, including the production of chemicals, food products, cosmetics and pharmaceuticals. As the methods used to increase the efficiency of their production are still being investigated, recent developments in the production of 1,2-PD, 1,3-PD and 2,3-BD, with regards to the metabolic engineering of production strains and the optimization of fermentation processes, are reviewed and discussed in this chapter. Keywords: 1,2-Propanediol (1,2-PD); 1,3-Propanediol (1,3-PD); 1,4-Butanediol (1,4-PD); 2,3-Butanediol (2,3-PD); culture conditions; medium composition; metabolic engineering