Biotechnological use of glycerol under different O2 availability conditions

M. JULIA PETTINARI; PABLO I. NIKEL; MANUEL S. GODOY; MARIELA MEZZINA; BEATRIZ S. MÉNDEZ

Glycerol: Production, Structure and Applications

Nova Science publishers

Lugar: Hauppage, NY; Año: 2012; p. 139 - 156

In recent years, a significant increase in the production of biodiesel has caused a sharp fall in the cost of glycerol, the main by-product of biodiesel synthesis. As a result, glycerol has become a very attractive substrate for biotechnological processes. Many bacterial metabolites of industrial interest are products of aerobic metabolism, such as antibiotics, amino acids, and other compounds; but others, including molecules used as biofuels (e.g., ethanol, butanol, and hydrogen), and other relevant biochemicals, such as 1,3-propanediol and succinate, are products of fermentative metabolism. Since carbon atoms in glycerol are more reduced than in glucose or other substrates commonly used in bioprocesses, the catabolism of this substrate normally consumes high amounts of oxygen, and only a handful of bacteria, including some members of the genus Enterobacter, Clostridium, and Klebsiella, were thought to be able to ferment this substrate in anaerobiosis. Recent research has shown that the facultative aerobe Escherichia coli can ferment glycerol, producing a number of different biotechnologically relevant molecules, like succinate and ethanol, and the heterologous product poly(3-hydroxybutyrate), both in microaerobiosis and in anaerobiosis. Several strategies have been used to increase the number of applications for glycerol as a substrate for bacterial processes, mostly based on modified bacterial strains that can efficiently produce different chemicals from this substrate. Manipulations to enhance the synthesis of various metabolic products from glycerol include several approaches to increase its availability inside the cells, or to decrease the synthesis of other metabolites. Mutations in the glp genes, involved in glycerol metabolism, or in genes involved in competing pathways, like ldhA, that encodes a D-lactate dehydrogenase, have been tested to increase the synthesis of several products from glycerol in different bacterial species. On the other hand, mutations in global regulator genes, especially in the redox-control pair arcAB, have been introduced in E. coli resulting in enhanced biosynthesis of reduced products from glycerol, mainly under microaerobic growth conditions. All these manipulations increase the number of possible uses of glycerol as a substrate for the obtention of a wide diversity of different biotechnological products using bacteria.