microbiology, Vol 140, 2451-2458, Copyright © 1994 by Society for General Microbiology
The physiological function of periplasmic glucose oxidation in phosphate-limited chemostat cultures of Klebsiella pneumoniae NCTC 418
ET Buurman, GJ ten Voorde and MJ Teixeira de Mattos
Department of Microbiology, E. C. Slater Institute, University of Amsterdam, The Netherlands.
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 this 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 nitrogen- and 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 to
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 phosphate-limited conditions (i) extensive futile cycling of
phosphate ions is absent and (ii) low concentrations of phosphate ions
limit intracellular degradation of glucose.(ABSTRACT TRUNCATED AT 250
WORDS)
