Glucose dehydrogenase (GDH)Glucose dehydrogenase (GDH) is a quino-
proteins which has the ability to oxidize glucose into gluconic acid. During catalytic
reaction, GDH needs pyrroloquinoline quinone (PQQ) and metal ions such as Ca
+2
or Mg
+2
(in vitro). Membrane GDHs (m-GDHs) are monomeric proteins of 88 kDa
with an N-terminal hydrophobic and large conserved PQQ-binding C-terminal
domains. This C-terminal domain has catalytic activity (Yamada et al. 1994 ).
However, N-terminal hydrophobic domain (residues 1–150) anchors the protein to
the membrane. It consists offive trans-membrane segments which play a major role
in anchoring the protein (Yamada et al. 1994 ). GDH plays a regulatory key in
bioenergetic role in the bacteria. Uptake of exogenous compounds such as amino
acids is due to trans-membrane proton motive force (PMF). Protons produced
during oxidation participate directly in the generation of trans-membrane proton
motive force (PMF). Therefore, this oxidative glucose pathway might be important
for the survival of bacteria.
Very little is known regarding genetic or biochemical mechanisms involved in
the synthesis of the GDH-PQQ halo enzyme. The possible inducers of halo enzyme
are manitol, glucose, gluconate, and manitol (Van Schie et al. 1987 ). However,
among several bacterial species, the difference in their constitutive and inducible
phenotypes is observed (Goldstein 1994 ).
4.3.2 Genetic Diversity and Role of Genetic Engineering
in P-Solubilization
4.3.2.1 Genetic Diversity of Phosphate-Solubilizing Microorganisms
Rhizosphere comprises of a huge microbial population of bacteria, fungi, protozoa,
and algae. Bacteria are the most copious among them. The selection and
Fig. 4.3 Prosthetic group of
bacterial quinoprotein
dehydrogenases
4 Endophytic Bacteria: Role in Phosphate Solubilization 73