S74: Systems analysis of the fermentative metabolism of glycerol and sugars in Escherichia coli

We have used a system-level approach (in silico and in vivo metabolic flux analysis) to obtain a better understanding of the fermentative metabolism of glucuronate, glucose, and glycerol in E. coli. The utilization of glucuronate and glucose was investigated with emphasis on the dissimilation of pyruvate via pyruvate formate-lyase (PFL) and pyruvate dehydrogenase (PDH). We found that the growth of a PDH-deficient strain on either glucose or glucuronate was significantly impaired. Metabolite balancing, biosynthetic ¹³C labeling of proteinogenic amino acids, and isotopomer balancing all indicated a large increase in the flux of the oxidative branch of the pentose phosphate pathway (ox-PPP) in response to the PDH deficiency. Since both the ox-PPP and PDH generate CO₂ and reducing equivalents, the aforementioned findings led the hypothesis that the role of PDH is to provide CO₂ (metabolism of glucose) and biosynthetic power (metabolism of glucuronate). Biochemical and molecular genetic approaches confirmed the proposed roles of PDH.

In vivo and in vitro flux analyses were used to investigate the fermentative metabolism of glycerol. This analysis confirmed a previously reported model in which the synthesis of both ethanol and 1,2-propanediol are required for this metabolic process. The analysis predicted an important role for pathways not previously reported to be involved in the fermentative utilization of glycerol.