Cyclic operation of the pentose phosphate, Entner-Doudoroff and glycolytic pathways in Pseudomonas putida

Abstract

The soil bacterium Pseudomonas putida KT2440 lacks a functional Embden-Meyerhof-Parnas (EMP) pathway, and glycolysis is known to proceed almost exclusively through the Entner-Doudoroff (ED) route. To investigate the raison d'etre of this metabolic arrangement, the distribution of periplasmic and cytoplasmic carbon fluxes were studied in glucose cultures of this bacterium by using 13C-labelled substrates, combined with quantitative physiology experiments, metabolite quantification, and in vitro enzymatic assays under both saturating and non-saturating, quasi in vivo conditions. Metabolic flux analysis demonstrated that 90% of the consumed sugar was converted into gluconate, entering central carbon metabolism as 6-phosphogluconate and further channeled into the ED pathway. Remarkably, about 10% of the triose phosphates were found to be recycled back to form hexose phosphates. This set of reactions merges activities belonging to the ED, the EMP (operating in a gluconeogenic fashion), and the pentose phosphate pathways to form an unforeseen metabolic architecture (EDEMP cycle). Determination of the NADPH balance revealed that the default metabolic state of P. putida KT2440 is characterized by a slight catabolic overproduction of reducing power. Cells growing on glucose thus run a biochemical cycle which favours NADPH formation. Since NADPH is required not only for anabolic functions but also for counteracting different types of environmental stress, such a cyclic operation may contribute to the physiological heftiness of this bacterium in its natural habitats.

Reference

Pablo Ivan Nikel, Max Chavarria, Tobias Fuhrer, Uwe Sauer and Victor de Lorenzo, external pagePseudomonas putida KT2440 Metabolizes Glucose Through a Cycle Formed by Enzymes of the Entner-Doudoroff, Embden-Meyerhof-Parnas, and Pentose Phosphate Pathwayscall_made, The Journal of Chemical Biology, in press