Physiology, Biochemistry and Molecular Genetics of Entner-Doudoroff Metabolism in Escherichia coli

The Entner-Doudoroffpathway (ED) forms the core of central metabolism in a large number of important microorganisms and is widely distributed, including the most deeply rooted Archae. In E. coli, the ED pathway is induced for gluconate catabolism, together with two systems for gluconate transport and phosphorylation. While it is generally appreciated that E. coil has evolved to grow in the intestinal habitat, little is known about which nutrients are used. Recent evidence suggests that metabolism of gluconate via the ED pathway is essential for E. coli to colonize the large intestine. The long term goal of this laboratory is to understand the roles of the ED pathway in nature and during the course of evolution of glycolytic pathways. We have begun to employ genomic information to study the four gluconate transporters, two gluconate kinases, and two regulatory proteins involved in gluconate metabolism. The GntI system for gluconate transport and phosphorylation contains two transporter genes, gntT and gntU. The work addresses how differential expression of these transporters impacts the physiology of growth on gluconate. Glucuronate, not gluconate, signals induction of gntP, another recently discovered gluconate transporter gene. Since the large intestine contains more glucuronate than gluconate, and since glucuronate induces the catabolic pathway for yet another sugar acid, it appears that glucuronate provides a general signal of sugar acid availability in nature. The importance of glucuronate-induction and GntP function for growth on gluconate is being investigated. The GntII subsidiary system for gluconate transport and phosphorylation (which normally functions only in the absence of the GntI system) also encodes two newly identified "dehydrogenase-like" enzymes which allow growth on L-idonic acid, with gluconate as a key intermediate. The biochemistry and physiology of the GntII pathway is being studied. Since gluconate appears to be an intermediate of the GntII pathway, and since gluconate is an inducer of other regulons, it seems important in terms of cellular economy to have crosstalk between these pathways. A protein that is both a positive regulator of GntII and a negative regulator of GntI is being characterized. The ultimate goal of this project is to elucidate the physiology, biochemistry and, regulation of sugar acid metabolism by E. coli in order to more fully understand its ecology. While it is generally appreciated that E.coli has evolved to grow in the intestinal habitat, little is known about which nutrients are used to support growth. Recent evidence suggests that metabolism of gluconate, an acidic form of the sugar glucose, is essential for E. coil to colonize the large intestine. In E. coil, the Entner-Doudoroff pathway is used for metabolism of gluconate and other sugar acids that are found in the large intestine. The Entner-Doudoroff pathway, as it operates in E. coli, is very complex; there are at least ten genes and three levels of genetic regulation involved in sugar acid metabolism. The goal of this project is to characterize the physiology, biochemistry and, regulation of sugar acid metabolism by E. coli in order to more fully understand the role of the Entner-Doudoroff pathway in colonization of the large intestine.