Syed Shams Yazdani, Anu Jose Mattam, and Ramon Gonzalez

Abstract

Glycerol (or glycerin) is a byproduct of biodiesel, oleo-chemical, and bioethanol production processes. Due to the tremendous growth of the biofuel industry, glycerol is now regarded as a waste product, often with a disposal cost associated with it. Glycerol is abundant and inexpensive, and it is also a highly reduced molecule, which offers the opportunity to produce fuels and reduced chemicals at yields higher than those obtained using common sugars. Few microorganisms are able to utilize glycerol in the absence of external electron acceptors to produce high-value chemicals such as 1,3-propanediol, succinic acid, propionic acid, and biosurfactants. However, microorganisms that are amenable to industrial applications, such as Escherichia coli and Saccharomyces cerevisiae, were thought to metabolize glycerol only via respiration. We showed recently that E. coli can fermentatively metabolize glycerol, and we established pathways, mechanisms, and conditions of this metabolic process. Our findings have opened up a new platform for engineering E. coli for the production of several fuels and chemicals. This chapter will focus on the production of ethanol with coproducts hydrogen and formate from glycerol and highlight ways of improving yields and productivities of these products.