S34: Understanding fermentative glycerol metabolism and its application for the production of fuels and reduced chemicals

Due to its availability, low-price, and higher degree of reduction than lignocellulosic sugars, glycerol has become an attractive carbon source for the production of fuels and reduced chemicals.  However, the highly reduced nature of carbon atoms in glycerol also results in significant challenges for its utilization under fermentative conditions, requiring a detailed understanding of the anaerobic fermentation of glycerol in order to unlock the full potential of microorganisms for the fermentative conversion of glycerol into fuels and chemicals.  The work presented here highlights a comprehensive experimental investigation into fermentative glycerol metabolism in Escherichia coli, which has elucidated several key pathways and mechanisms.  The activity of both the fermentative and respiratory glycerol dissimilation pathways was found to be important for maximum glycerol utilization, a consequence of the metabolic cycle and downstream effects created by the essential involvement of PEP-dependent dihydroxyacetone kinase (DHAK) in the fermentative glycerol dissimilation pathway.  The central role of this enzyme is also tied not only to the importance of several additional enzymes, such as fumarate reductase and pyruvate kinase, but is also of critical significance for the design of metabolic engineering strategies for the production of fuels and chemicals from glycerol.  Using this improved understanding of fermentative glycerol metabolism as a platform, E. coli has been engineered to produce high yields and titers of ethanol (19.8 g/L, 0.46 g/g), co-produced along with hydrogen, and 1,2-propanediol (5.6 g/L, 0.21 g/g) from glycerol, demonstrating its potential as a carbon source for the production of fuels and reduced chemicals.