A.-P. Zeng, H. Biebl, and W.-D. Deckwer

Biochemical Engineering Division, Gesellschaft fur Biotechnologische
Forschung mbH, Mascheroder Weg 1, D—38124 Braunschweig, Germany

The microbial conversion of glycerol to 1,3-propanediol has recently re­ceived much attention because of the appealing properties of 1,3-propa­nediol and the anticipated surplus of glycerol on the market. Our knowledge of the metabolic pathway, the intrinsic metabolic potential and kinetic limitation of this bioconversion process has been substantially augmented. Progress has also been made in improving the process perfor­mance and strains both on process engineering and molecular biology levels. These recent advances are summarized in this communication. Further research and development needs are also discussed.

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The fatty acid is used by the oleo-chemical industry as a feedstock for the production of detergents and other chemical intermediates. Glycerol has been traditionally used in the production of pharmaceuticals, cosmetics, resins, food, beverages, tabacco as well as cellophan and explosives. The oleo-chemical industry has considerably grown in the last decade due to the relatively low price increase of natural fats compared to petro­chemicals. However, no major new application has been found for glycerol during this period, leading to a surplus of glycerol on the market. This surplus of glycerol is expec­ted to expand further with the envisaged application of rape-seed oil as a diesel substitu — © 1997 American Chemical Society

te. The conversion of rape-seed oil to an appropriate diesel fuel yields about 10% glyce­rol by weight (13,15). The use of glycerol as a stock compound for chemical processing is therefore of industrial interest.

One potential use of surplus glycerol is its conversion to 1,3-propanediol (1,3- PD). Recently, this bioconversion has received world-wide attention. It is mainly driven by two factors. First, 1,3-PD is an appealing product and finds applications in the syn­thesis of heterocycles and polyesters. Polyesters based on 1,3-PD have special proper­ties such as biodegradability, improved light stability, anti-sliding and re-stretching qualities when used as material for the manufacture of carpet ware in combination with terephthalic acid. Recently, two large chemical companies Shell and Degussa anounced the commercialization of 1,3-PD production based on petrochemical feedstocks. Se­cond, 1,3-PD from biological route represents a rare case for a primary chemical the biological production of which is competitive or even more economical compared to the chemical route (12). This fermentation process has been successfully scaled up on a pilot plant scale with batch culture of Clostridium butyricum (17). The recovery and purification of 1,3-PD has also been intensively studied. Recently, Deckwer (12) revie­wed the microbial conversion of glycerol to 1,3-PD, covering major work up to about 1993 and including economical aspects. In this communication advances achieved in the last few years are briefly summarized, focusing mainly on pathway, stoichiometric and kinetic analysis, strain improvement and process optimization.