It is also used as antifreeze for de-icing aircrafts at airports as it lowers the freezing point of water. Recent applications include use as a humectant and a preservative. It is used in cosmetics, pharmaceutical preparations and also in electronic cigars2.
1,2-Propanediol as well as 1,3-Propanediol can be manufactured though bioengineered microorganisms. By turning on and off some genes, it is possible to make the microorganism overproduce a specific metabolic product. As shown in figure 2, the intermediate metabolism of Escherichia coli can be shifted to produce 1,2 and 1,3-propanediol using enzymes such as aldose reductase from rat lens, E. coli glycerol dehydrogenase and Klebsiella pneumoniae glycerol dehydrogenase and 1,3-propanedioloxidoreductase4. There are various biochemical pathways through which 1,2-propanediol can be produced.
The production of 1,2-propanediol through sugar fermentation has long been reported in bacteria5. Many subsequent studies have reported the production of this glycol in other bacteria and yeasts. Production of 1,2-propanediol by wild-type E. coli from common sugars is not known. As back as 1981, 1,2-propanediol was found to be produced through a direct route from deoxy sugars by E.coli6. It was shown that E. coli can grow on the L-fucose and L-rhamnose deoxy sugars as sole carbon and energy sources resulting in the production of propanediol. The first instance of metabolic engineering to produce 1,2-propanediol was when Altaras and Cameron metabolically bioengineered the 1,2-propanediol pathway in E. coli7. In 1999, they reported that E. coli that overexpressed methylglyoxal synthase gene produced 1,2-propanediol. Expression of methylglyoxal synthase or glycerol dehydrogenase led to anaerobic production of around 0.25 g of 1,2-propanediol per liter. The yield was found to be higher both the enzymes were coexpressed7.
After their first report of