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.