The physiological function of periplasmic glucose oxidation in phosphate-limited chemostat cultures of Klebsiella pneumoniae NCTC 418

Abstract

Periplasmic oxidation of glucose into gluconate and 2-ketogluconate in Klebsiella pneumoniae occurs via glucose dehydrogenase (GDH) and gluconate dehydrogenase (GaDH), respectively. Since, as is shown here, in the presence of glucose, gluconate and 2-ketogluconate are not further metabolized intracellularly the physiological function of t h i s periplasmic route was studied. It was found that periplasmic oxidation of glucose could function as an alternative production route of ATP equivalents. Instantaneous activation of either GDH or GaDH reduced the rate of degradation of glucose via glycolysis and the tricarboxylic acid (TCA) cycle in vivo. Furthermore, aerobic, magnesium-and phosphate-limited chemostat cultures with glucose as the carbon source showed high GDH plus GaDH activities in contrast to nitrogenand sulphate-limited cultures. However, when fructose, which is not degraded by GDH, was the carbon source, specific oxygen consumption rates under these four conditions were essentially the same. The latter observation suggests that high transmembrane phosphate gradients which are supposedly present under phosphate-limited conditions do not cause high energetic demands due t o futile cycling of phosphate ions. In addition, dissipation of the transmembrane phosphate gradient of phosphate-limited cells immediately increased the rate of intracellular glucose degradation. It is concluded that under phosphatelimited conditions (i) extensive futile cycling of phosphate ions is absent and (ii) low concentrations of phosphate ions limit intracellular degradation of glucose. Glyceraldehyde-3-phosphate dehydrogenase (GADPH) activities of cell-free extracts of glucose-grown cells harvested from aerobic chemostat cultures limited in various nutrients showed that a t least a tenfold overcapacity in GAPDH activity was present under phosphate-limited conditions with respect to the steady-state carbon fluxes through this enzyme. The physiological significance of t h i s adaptation and the possible role of GDH and GaDH are discussed.

Mineral Phosphate Solubilization in Burkholderia tropica Involves an Inducible PQQ-Glucose Dehydrogenase

“…In some microorganisms, the phenomenon of phosphate-starvation-inducible gene expression involves specific phosphate regulated genes and several of these are also inducible by other stress conditions [37]. Therefore, P availability seems to play an important role in regulating PQQ-GDH expression in some bacteria [38][39][40] including B. tropica, as shown in this work.…”

Biphasic cellular adaptations and ecological implications of Alteromonas macleodii degrading a mixture of algal polysaccharides

“…The exclusive upregulation of LamPUL1 and LamPUL2 with laminarin but not glucose indicated finetuned sensing of polymeric vs. monomeric glucose, comparable to Gramella forsetii [16]. In this context, only laminarin induced the upregulation of gene cluster Alt831_00338⎼47 (Table S3) encoding three xylose/glucose isomerases, two glucose oxidoreductases and a gluconate 2-dehydrogenase, suggesting that only polymeric glucose is partially channeled into oxidative degradation to generate additional reducing equivalents [88].…”

Phosphate-solubilization mechanism and in vitro plant growth promotion activity mediated by Pantoea eucalypti isolated from Lotus tenuis rhizosphere in the Salado River Basin (Argentina)

“…Evaluation of a large number of samples from a wide range of soil types has shown that, in general, highly efficient PSB are Gram‐Negative and utilize the direct oxidation glucose pathway to produce gluconic and 2‐ketogluconic acids (Krishnaraj and Goldstein 2001). Conversion of glucose to gluconic acid is facilitated by pyrolloquinoline quinone‐dependent glucose dehydrogenase (PQQ‐GDH) and gluconic acid oxidation to 2‐ketogluconic takes place via the FAD‐linked gluconate dehydrogenase (GADH) (Buurman et al. 1994; Buch et al.…”