Analysis of gluconate metabolism for pyruvate production in engineered Escherichia coli based on genome-wide transcriptomes.

For pyruvate-producing strains, intracellular reduced nicotinamide adenine dinucleotide (NADH) accumulation is the main reason for the glycolysis inhibition. Comparing with glucose, using sodium gluconate as carbon source brought a decrease in NADH production and an increase in pyruvate production in engineered strain YP211. In order to explore the metabolic advantages of gluconate, genome-wide transcriptome analysis was employed to compare the metabolic differences between the two carbon sources. The results showed that the transcription of the genes gntU, gntK, and gntT responsible for transport and phosphorylation of gluconate, and genes edd and eda belonging to the Entner-Doudoroff (ED) pathway, was significantly enhanced. This suggested that the shortest route for the synthesis of pyruvate from gluconate was activated, and the synthesis of NADH was halved. Besides, the transcription of genes glpABCDTKF related to the glycerol metabolism was significantly enhanced, which might be because glycerol metabolism pathways were activated in the absence of glucose. These results provided valuable information for the further design of metabolic pathways in the construction of pyruvate-producing strains. SIGNIFICANCE AND IMPACT OF THE STUDY: Comparing with glucose, using sodium gluconate as carbon source brought a decrease in nicotinamide adenine dinucleotide and an increase in pyruvate production in engineered strain YP211. From the genome-wide transcriptome analysis, the Entner-Doudoroff pathway was activated strongly in gluconate metabolism, which innovatively provided a shorter and more effective pathway for pyruvate production.

Gluconate as suitable potential reduction supplier in Corynebacterium glutamicum: Cloning and expression of gntP and gntK in Escherichia coli

Corynebacterium glutamicum is widely used in the industrial production of amino acids. We have found that this bacterium grows exponentially on a mineral médium supplemented with gluconate. Gluconate permease and Gluconokinase are expressed in an inducible form and, 6-phosphogluconate dehydrogenase, although constituvely expressed, shows a 3-fold higher specific level in gluconate grown cells than those grown in fructose under similar conditions. Interestingly, these activities are lower than those detected in the strain Escherichia coli Ml-8, cultivated under similar conditions. Additionally, here we also confirmed that this bacterium lacks 6-phosphogluconate dehydratase activity. Thus, gluconate must be metabolized through the pentose phosphate pathway. Genes encoding gluconate transport and its phosphorylation were cloned from C. glutamicum, and expressed in suitable E. coli mutants. Sequence analysis revealed that the amino acid sequences obtained from these genes, denoted as gntP and gntK, were similar to those found in other bacteria. Analysis of both genes by RT-PCR suggested constitutive expression, in disagreement with the inducible character of their corresponding activities. The results suggest that gluconate might be a suitable source of reduction potential for improving the efficiency in cultures engaged in amino acids production. This is the first time that gluconate specific enzymatic activities are reported in C. glutamicum.