Mutations that disrupt either the pqq or the gdh gene of Rahnella aquatilis abolish the production of an antibacterial substance and result in reduced biological control of grapevine crown gall

Rahnella aquatilis HX2, a biocontrol agent for grapevine crown gall caused by Agrobacterium vitis, produces an antibacterial substance that inhibits the growth of A. vitis in vitro. In this study, we show that MH15 and MH16, two Tn5-induced mutants of HX2, have lost their abilities to inhibit A. vitis and have reduced biocontrol activities; they grow in logarithmic phase at a rate similar to that of the wild type and have single Tn5 insertions. They are also impaired in producing pyrroloquinoline quinone (PQQ) or glucose dehydrogenase (GDH). Complementation of MH15 and MH16 with cosmid clones of CP465 and CP104 from an HX2 DNA library restored the antibiosis, biocontrol, and PQQ or GDH production phenotypes. A 6.7-kb BamHI fragment from CP465 that fully restored the MH15-affected phenotypes was cloned and sequenced. Sequence analysis of the mutated DNA region resulted in the identification of seven open reading frames (ORFs), six of which share significant homology with PQQ-synthesizing genes in other bacteria, designated pqqA through pqqF. Meanwhile, A 5.5-kb PstI fragment from CP104 fully complemented the MH16 mutant and contained a single ORF highly similar to that of genes coding for GDHs. An in-frame gdh deletion mutant has the same phenotypes as the Tn5 mutant of MH16. Complementation of both deletion and Tn5 gdh mutants restored the affected phenotypes to wild-type levels. Our results suggest that an antibacterial substance plays a role in biocontrol of A. vitis by HX2.

Co-expression of P450 BM3 and glucose dehydrogenase by recombinant Escherichia coli and its application in an NADPH-dependent indigo production system

P450 BM3 mutant can catalyze indole to indoxyl, and indoxyl can dimerize to form indigo. But the reaction catalyzed by P450 BM3 requires NADPH, as coenzyme regeneration is very important in this system. As we know, when glucose dehydrogenase oxidizes glucose to glucolactone, NADH or NADPH can be formed, which can contribute to NADPH regeneration in the reaction catalyzed by P450 BM3. In this paper, a recombinant Escherichia coli BL21 (pET28a (+)-P450 BM3-gdh0310) was constructed to co-express both P450 BM3 gene and glucose dehydrogenase (GDH) gene. To improve the expression level of P450 BM3 and GDH in E. coli and to avoid the complex and low-efficiency refolding operation in the purification procedure, the expression conditions were optimized. Under the optimized conditions, the maximum P450 BM3 and GDH activities amounted to 8173.13 and 0.045 U/mg protein, respectively. Then bioconversion of indole to indigo was carried out by adding indole and glucose to the culture after improved expression level was obtained under optimized conditions, and 2.9 mM (760.6 mg/L) indigo was formed with an initial indole concentration of 5 mM.

High-level expression of recombinant glucose dehydrogenase and its application in NADPH regeneration

Two glucose dehydrogenase (E.C. 1.1.1.47) genes, gdh223 and gdh151, were cloned from Bacillus megaterium AS1.223 and AS1.151, and were inserted into pQE30 to construct the expression vectors, pQE30-gdh223 and pQE30-gdh151, respectively. The transformant Escherichia coli M15 with pQE30-gdh223 gave a much higher glucose dehydrogenase activity than that with the plasmid pQE30-gdh151. Thus it was used to optimize the expression of glucose dehydrogenase. An proximately tenfold increase in GDH activity was achieved by the optimization of culture and induction conditions, and the highest productivity of glucose dehydrogenase (58.7 U/ml) was attained. The recombinant glucose dehydrogenase produced by E. coli M15 (pQE30-gdh223) was then used to regenerate NADPH. NADPH was efficiently regenerated in vivo and in vitro when 0.1 M glucose was supplemented concomitantly in the reaction system. Finally, this coenzyme-regenerating system was coupled with a NADPH-dependent bioreduction for efficient synthesis of ethyl (R)-4-chloro-3-hydroxybutanoate from ethyl 4-chloro-3-oxobutanoate.

Surface charge engineering of PQQ glucose dehydrogenase for downstream processing

The ion-exchange chromatography behavior of recombinant glucose dehydrogenase harboring pyrroloquinoline quinone (PQQGDH) was modified to greatly simplify its purification. The surface charge of PQQGDH was engineered by either fusing a three-arginine tail to the C-terminus of PQQGDH (PQQGDH+Arg3) or by substituting three residues exposed on the surface of the enzyme to Arg by site-directed mutagenesis (3RPQQGDH). During cation exchange chromatography, both surface charge-engineered enzymes eluted at much higher salt concentrations than the wild-type enzyme. After the chromatography purification step, both PQQGDH+Arg3 and 3RPQQGDH appeared as single bands on SDS-PAGE, while extra bands appeared with the wild-type protein sample. Although all tested kinetic parameters of both engineered enzymes are similar to those of wild type, both modifications resulted in enzymes with increased thermal stability. Our achievements have resulted in the greater production of an improved quality PQQGDH by a simplified process.

Simultaneous synthesis of enantiomerically pure (R)-1-phenylethanol and (R)-alpha-methylbenzylamine from racemic alpha-methylbenzylamine using omega-transaminase/alcohol dehydrogenase/glucose dehydrogenase coupling reaction

A simultaneous synthesis of (R)-1-phenylethanol and (R)-alpha-methylbenzylamine from racemic alpha-methylbenzylamine was achieved using an omega-transaminase, alcohol dehydrogenase, and glucose dehydrogenase in a coupled reaction. Racemic alpha-methylbenzylamine (100 mM) was converted to 49 mM (R)-1-phenylethanol (> 99% ee) and 48 mM (R)-alpha-methylbenzylamine (> 98% ee) in 18 h at 37 degrees C. This method was also used to overcome product inhibition of omega-TA by the ketone product in the kinetic resolution of racemic amines at high concentration.

Cloning and expression of the gene encoding catalytic subunit of thermostable glucose dehydrogenase from Burkholderia cepacia in Escherichia coli

We have cloned a 1620-nucleotide gene encoding the catalytic subunit (alpha subunit) of a thermostable glucose dehydrogenase (GDH) from Burkholderia cepacia. The FAD binding motif was found in the N-terminal region of the alpha subunit. The deduced primary structure of the alpha subunit showed about 48% identity to the catalytic subunits of sorbitol dehydrogenase (SDH) from Gluconobacter oxydans and 2-keto-D-gluconate dehydrogenases (2KGDH) from Erwinia herbicola and Pantoea citrea. The alpha subunit of B. cepacia was expressed in Escherichia coli in its active water-soluble form, showing maximum dye-mediated GDH activity at 70 degrees C, retaining high thermal stability. A putative open reading frame (ORF) of 507 nucleotides was also found upstream of the alpha subunit encoding an 18-kDa peptide, designated as gamma subunit. The deduced primary structure of gamma subunit showed about 30% identity to the small subunits of the SDH from G. oxydans and 2KGDHs from E. herbicola and P. citrea.

Cloning of a Serratia marcescens DNA fragment that induces quinoprotein glucose dehydrogenase-mediated gluconic acid production in Escherichia coli in the presence of stationary phase Serratia marcescens

Serratia marcescens ER2 was isolated from an endorhizosphere sample based on its high level of mineral phosphate solubilizing (MPS) activity. This phenotype was correlated with expression of the direct oxidation pathway. An ER2 plasmid library constructed in Escherichia coli strain DH5alpha was screened for MPS activity. A recombinant clone DH5alpha (pKG3791) was capable of gluconic acid (GA) production and tricalcium phosphate solubilization but only in the presence of stationary phase ER2 cells. GA production in DH5alpha (pKG3791) was apparently the result of the quinoprotein glucose dehydrogenase activity because AG121 (a Tn5 knockout of gcd) carrying pKG3791 did not produce GA under the same conditions. GA production by DH5alpha (pKG3791) was not observed when ER2 was replaced by another PQQ-producing strain bacterium. These data add to a growing body of evidence that E. coli contains some type of PQQ biosynthesis pathway distinct from those previously characterized in Gram-negative bacteria and that these genes may be induced under appropriate conditions.

Heterologous overexpression of glucose dehydrogenase from the halophilic archaeon Haloferax mediterranei, an enzyme of the medium chain dehydrogenase/reductase family

The first gene encoding a glucose dehydrogenase (GDH) from a halophilic organism has been sequenced. Amino acid sequence alignments of GDH from Haloferax mediterranei show a high degree of homology with the thermoacidophilic GDHs and with other enzymes from the medium chain dehydrogenase/reductase family. Heterologous overexpression using the mesophilic organism Escherichia coli as the host has been performed and the expression product was obtained as inclusion bodies. To obtain the halophilic enzyme in its native form refolding and reactivation in a saline environment were required. A pure and highly concentrated sample of the enzyme was obtained using a purification procedure based on the protein's halophilicity. This method may be useful as a general procedure for purifying other halophilic proteins from mesophilic hosts.

Antioxidant enzymes are induced during recovery from acute lung injury

OBJECTIVE

To determine the contribution of the pulmonary antioxidant defense enzymes of the hexose monophosphate (HMP) shunt and glutathione systems to recovery from oxidant-mediated lung injury in an animal model shown to closely resemble the clinical syndrome of acute respiratory distress syndrome.

DESIGN

Prospective, controlled laboratory study on phorbol myristate acetate (PMA)-induced lung injury in rabbits.

SETTING

Animal research laboratory.

SUBJECTS

Rabbits were injected with PMA (80 microg/kg) for 3 consecutive days. Control animals received normal saline.

MEASUREMENTS AND MAIN RESULTS

Lungs were harvested at 24, 48, 72, and 96 hrs (n = 5/time point) after PMA injection or after the third injection of normal saline in control animals (n = 6). The cytosolic fraction from lung and bronchial alveolar lavage (BAL) fluid was used for measurements of HMP shunt and glutathione enzymes. Pulmonary activity peaked at 48 hrs post-PMA injury with a 40% increase in glucose-6-phosphate dehydrogenase activity and a 32% increase in 6-phosphogluconate dehydrogenase activity over control levels. BAL activity was maximal at 72 hrs with an increase of 98% in glucose-6-phosphate dehydrogenase and 346% in 6-phosphogluconate dehydrogenase activities. Glutathione peroxidase was maximally induced by 77% at 48 hrs in BAL and by 107% at 24 hrs in lung. Glutathione reductase activity did not increase significantly in either lung or BAL.

CONCLUSIONS

The observed induction of the antioxidant enzymes in response to PMA suggests that both the HMP shunt and the glutathione systems contribute to the recovery phase of oxidant-mediated lung injury. The inability of natural host defenses to regenerate reduced glutathione may explain failure of recovery from acute respiratory distress syndrome and suggests an avenue for clinical intervention.

Escherichia coli transformant expressing the glucose dehydrogenase gene from Bacillus megaterium as a cofactor regenerator in a chiral alcohol production system

Escherichia coli JM109 (pGDA2) overexpressing the glucose dehydrogenase (GDH) gene from Bacillus megaterium IWG3 was examined for use as a cofactor regenerator. In the asymmetric reduction of ethyl 4-chloro-3-oxobutanoate by E. coli JM109 (pKAR) which is an aldehyde reductase-overproducing transformant, E. coli JM109 (pGDA2) can act as an NADPH regenerator with NADP+ and glucose, similarly to commercially available GDH.

Production, characterization, and reconstitution of recombinant quinoprotein glucose dehydrogenase (soluble type; EC 1.1.99.17) apoenzyme of Acinetobacter calcoaceticus

Soluble, periplasmic quinoprotein glucose dehydrogenase of Acinetobacter calcoaceticus (sGDH; EC 1.1.99.17) was produced in good yield in the apoenzyme form (without the cofactor pyrroloquinoline quinone, PQQ) by an Escherichia coli recombinant strain provided with a plasmid containing the gene under control of a lac promoter. Structural analysis of the purified apoenzyme revealed that the E. coli strain used produces the correct mature protein. Titration of the apoenzyme with PQQ in the presence of Ca2+ showed that a linear relation exists between the amount of added PQQ and activity observed, and that the subunit and PQQ associate in a molar ratio of 1:1. Based on spectral and enzymatic criteria, it is concluded that the present holoenzyme preparation has a better quality than the previously described preparations of authentic holoenzyme. As isolated here, the recombinant apoenzyme was in the dimeric form. Partial monomerization occurred upon gel filtration in a buffer with chelator and the process could be reversed with Ca2+. PQQ binds to the dimer in the presence of chelator, not to the monomer. However, the PQQ-containing dimer was not active and showed an unusual absorption spectrum which was slowly converted into a PQQH2-like spectrum when glucose was added. Full restoration of activity was achieved upon addition of Ca2+ and the spectra were immediately converted into those of normal holoenzyme in the oxidized and reduced form, respectively. Addition of chelator to holoenzyme did not lead to inactivation or monomerization. It is concluded, therefore, that Ca2+ has a dual role in this enzyme, being required for dimerization of the subunits as well as for functionalization of the bound PQQ, and that it is more firmly attached to the holoenzyme than to the apoenzyme.

A somatic reproductive organ enhancer complex activates expression in both the developing and the mature Drosophila reproductive tract

The Glucose dehydrogenase (Gld) gene is highly expressed in the mature Drosophila reproductive tract. Unlike several other Drosophila genes which function in reproductive physiological processes, Gld is also expressed extensively in the developing reproductive tract during metamorphosis. Proximal promoter elements drive Gld expression in a variety of tissues throughout development, but not in the reproductive tract. Herein, we have identified a somatic reproductive organ enhancer complex (SREC) containing multiple redundant enhancer modules in Gld intron I (+639 to +3906 nt). The SREC, in combination with the Gld promoter, activates beta galactosidase reporter gene expression in both the developing and the mature reproductive tract. The SREC activates a heterologous hsp70 promoter in the ejaculatory duct, but not in other reproductive tract tissues, suggesting that the SREC acts synergistically with Gld promoter proximal elements. Through deletion analysis we have delimited a 361-nt region of the SREC that is involved in ejaculatory duct/oviduct-specific expression. The ejaculatory duct/oviduct enhancer retains the ability to activate expression in both the developing and the mature reproductive tract, suggesting that the same basic enhancer elements activate Gld expression during metamorphosis and in adults. A model of the evolution of Gld expression in the ejaculatory duct and oviduct is presented.

Increased production of recombinant pyrroloquinoline quinone (PQQ) glucose dehydrogenase by metabolically engineered Escherichia coli strain capable of PQQ biosynthesis

We have previously shown that the production of recombinant Escherichia coli PQQGDH was greatly improved by using a medium supplemented with the cofactor PQQ, which is not synthesized in E. coli. We show here that the increase in the accumulated PQQGDH is due to the increased stability of the holo-enzyme over apo-enzyme, using recombinant Acinetobacter calcoaceticus PQQGDH. In order to achieve cost-effective PQQGDH production, we incorporated the genes for PQQ biosynthetic pathway from Klebsiella pneumoniae into E. coli, which as a result allowed E. coli to produce PQQ. Using this metabolically engineered E. coli strain as a host, a 10-fold increase in the production of recombinant A. calcoaceticus PQQGDH was achieved, compared to the condition without PQQ and MgCl2.

Effect of PQQ glucose dehydrogenase overexpression in Escherichia coli on sugar-dependent respiration

Pyrroloquinoline quinone glucose dehydrogenase (PQQGDH) was overexpressed in Escherichia coli, and its impact on sugar-dependent respiration was investigated. Sugar-dependent respiration patterns under PQQGDH overexpression can be devided into two types. The first type involves D-glucose and D-mannose, which are utilized by the phosphotransferase system (PTS) and are also the substrates of PQQGDH. As a result of PQQGDH overexpression, the apparent Km value of sugar-dependent respiration shifted to higher concentration compared with E. coli parental cells. The second type included D-xylose and D-galactose, which are the substrates of PQQGDH, but not the PTS sugars. PQQGDH overexpressing cells showed much higher respiration than parental cells. These results suggested that PQQGDH overexpression may alter sugar utilization preferences in E. coli, suggesting further possible applications in metabolic engineering for carbon source utilization.

Elucidation of the region responsible for EDTA tolerance in PQQ glucose dehydrogenases by constructing Escherichia coli and Acinetobacter calcoaceticus chimeric enzymes

We constructed various chimeric PQQ glucose dehydrogenases (PQQGDHs) from an EDTA-sensitive PQQGDH from Escherichia coli and an EDTA-tolerant PQQGDH from Acinetobacter calcoaceticus by homologous recombination of their structural genes. The EDTA tolerance of the resulting chimeric enzymes was investigated. Our results demonstrated that EDTA tolerance of PQQGDHs can be completely altered by substituting each corresponding region. The EDTA tolerance of A. calcoaceticus PQQGDH is mostly within a region composed of about 90 amino acid residues located between 45 and 56% of the distance from the N-terminal region.

Cloning of an Erwinia herbicola gene necessary for gluconic acid production and enhanced mineral phosphate solubilization in Escherichia coli HB101: nucleotide sequence and probable involvement in biosynthesis of the coenzyme pyrroloquinoline quinone

Escherichia coli is capable of synthesizing the apo-glucose dehydrogenase enzyme (GDH) but not the cofactor pyrroloquinoline quinone (PQQ), which is essential for formation of the holoenzyme. Therefore, in the absence of exogenous PQQ, E. coli does not produce gluconic acid. Evidence is presented to show that the expression of an Erwinia herbicola gene in E. coli HB101(pMCG898) resulted in the production of gluconic acid, which, in turn, implied PQQ biosynthesis. Transposon mutagenesis showed that the essential gene or locus was within a 1.8-kb region of a 4.5-kb insert of the plasmid pMCG898. This 1.8-kb region contained only one apparent open reading frame. In this paper, we present the nucleotide sequence of this open reading frame, a 1,134-bp DNA fragment coding for a protein with an M(r) of 42,160. The deduced sequence of this protein had a high degree of homology with that of gene III (M(r), 43,600) of a PQQ synthase gene complex from Acinetobacter calcoaceticus previously identified by Goosen et al. (J. Bacteriol. 171:447-455, 1989). In minicell analysis, pMCG898 encoded a protein with an M(r) of 41,000. These data indicate that E. coli HB101(pMCG898) produced the GDH-PQQ holoenzyme, which, in turn, catalyzed the oxidation of glucose to gluconic acid in the periplasmic space. As a result of the gluconic acid production, E. coli HB101(pMCG898) showed an enhanced mineral phosphate-solubilizing phenotype due to acid dissolution of the hydroxyapatite substrate.

Organ-specific patterns of gene expression in the reproductive tract of Drosophila are regulated by the sex-determination genes

The sex-determination genes of Drosophila act to repress the developmental pathway for the internal somatic reproductive organs of the opposite sex. By misregulating this pathway during preadult development, the organ-specific expression pattern of the glucose dehydrogenase gene (Gld) in the reproductive tract of adult flies has been changed without a concomitant sexual transformation of the reproductive organs. Misregulation of the tra, tra-2, and dsx genes leads to very similar patterns of ectopic expression of Gld. The induced ectopic patterns of Gld expression at the adult stage occur in a small subset of organs which all normally express the Gld gene during their morphogenesis. These ectopic patterns are irrevocably set during late larval-early pupal development. The normal pattern of Gld expression in several other Drosophila species is quite similar to the ectopic patterns which we have generated in D. melanogaster, suggesting that the interspecific variation in Gld expression may result from variation in the expression of the sex-determination genes.

Cloning, nucleotide sequence, and regulation of the Bacillus subtilis gpr gene, which codes for the protease that initiates degradation of small, acid-soluble proteins during spore germination

The gpr gene, which codes for the protease that initiates degradation of small, acid-soluble proteins during spore germination, has been cloned from Bacillus megaterium and Bacillus subtilis, and its nucleotide sequence has been determined. Use of a translational gpr-lacZ fusion showed that the B. subtilis gpr gene was expressed primarily, if not exclusively, in the forespore compartment of the sporulating cell, with expression taking place approximately 1 h before expression of glucose dehydrogenase and ssp genes. gpr-lacZ expression was abolished in spoIIAC (sigF) and spoIIIE mutants but was reduced only approximately 50% in a spoIIIG (sigG) mutant. However, the kinetics of the initial approximately 50% of gpr-lacZ expression were unaltered in a spoIIIG mutant. The in vivo transcription start site of gpr has been identified and found to be identical to the in vitro start site on this gene with either E sigma F or E sigma G. Induction of sigma G synthesis in vivo turned on gpr-lacZ expression in parallel with synthesis of glucose dehydrogenase. These data are consistent with gpr transcription during sporulation first by E sigma F and then by E sigma G.

Purification and site-specific immobilization of genetically engineered glucose dehydrogenase on thiopropyl-Sepharose

The gene encoding glucose dehydrogenase (EC 1.1.1.47) from Bacillus subtilis was inserted in a plasmid 1.0 kb downstream from a lac promoter, resulting in a 70-fold higher production of the enzyme when expressed in Escherichia coli. A glucose dehydrogenase mutant containing a cysteine residue at position 44 could also be expressed at the same high level. This single cysteine residue was used as an 'affinity tag' to simplify the purification procedure as well as for site-specific immobilization of glucose dehydrogenase on Thiopropyl-Sepharose. This enzyme was purified to homogeneity with a final recovery of 65% and a specific activity of 240 U/mg. The oriented immobilization resulted in increased thermal stability.

Regulated expression of heterologous genes inBacillus subtilis using the Tn10 encodedtet regulatory elements

The Escherichia coli-derived tet regulatory elements from Tn10 have been used to construct vectors allowing the regulated, inducible, high-level expression of foreign genes in Bacillus subtilis. While the wild-type tet promoters are inactive in B. subtilis, a synthetic mutant tet sequence with improved promoter consensus sequences and upstream poly A blocks shows activity in B. subtilis. The expression of an indicator cat gene is inducible by sublethal amounts of tetracycline, indicating that the Tet repressor protein and the tet operator sequences are functional. However, the inducibility and maximal expression are not sufficient in this construct. To improve these properties a tet operator sequence was placed between the -35 and -10 boxes of the B. subtilis-derived very strong xyl promoter. In the presence of a tetR gene this construct is about 100-fold inducible and has high promoter strength, but some basal expression. This is avoided by placing a second tet operator downstream resulting in no detectable basal expression at the expense of reduced inducibility. Using the system with a single tet operator inducible expression of glucose dehydrogenase from B. megaterium was obtained at a very high level, and inducible expression of human single-chain urokinase-like plasminogen activator was achieved at the same level as in E. coli. Unlike in E. coli, the product was not degraded up to 4 h after induction in B. subtilis. These results demonstrate that the regulated expression vector described here should be very useful for production of foreign gene products from B. subtilis cultures.

Developmental expression of the glucose dehydrogenase gene in Drosophila melanogaster

The Gld gene of Drosophila melanogaster is transiently expressed during every stage of development. The temporal pattern of Gld expression is highly correlated with that of ecdysteroids. Exogeneous treatment of third instar larvae with 20-hydroxyecdysone induces the accumulation of Gld mRNA in the hypoderm and anterior spiracular gland cells. During metamorphosis Gld is expressed in a variety of tissues derived from the ectoderm. In the developing reproductive tract, Gld mRNA accumulates in the female spermathecae and oviduct and in the male ejaculatory duct and ejaculatory bulb. These four organs are derived from closely related cell lineages in the genital imaginal disc. Since the expression of Gld is not required for the development of these reproductive structures, this spatial pattern of expression is most likely a fortuitous consequence of a shared regulatory factor in this cell lineage. At the adult stage a high level of the Gld mRNA is only observed in the male ejaculatory duct.

Physiological significance and bioenergetic aspects of glucose dehydrogenase

The regulation of the PQQ-linked glucose dehydrogenase in different organisms is reviewed. It is concluded that this enzyme functions as an auxiliary energy-generating mechanism, because it is maximally synthesized under conditions of energy stress. It is now definitively established that the oxidation of glucose to gluconate generates metabolically useful energy. The magnitude of the contribution of the oxidation of glucose to gluconate via this enzyme to the growth yield of organisms such as Acinetobacter calcoaceticus is not yet clear.

Effects of growth rate and oxygen tension on glucose dehydrogenase activity in Acinetobacter calcoaceticus LMD 79.41

The regulation of the synthesis of the quinoprotein glucose dehydrogenase (EC 1.1.99.17) has been studied in Acinetobacter calcoaceticus LMD 79.41, an organism able to oxidize glucose to gluconic acid, but unable to grow on both compounds. Glucose dehydrogenase was synthesized constitutively in both batch and carbon-limited chemostat cultures on a variety of substrates. In acetate-limited chemostat cultures glucose dehydrogenase levels and the glucose-oxidizing capacity of whole cells were dependent on the growth rate. They strongly increased at low growth rates at which the maintenance requirement of the cells had a pronounced effect on biomass yield. Cultures grown on a mixture of acetate and glucose in carbon and energy-limited chemostat cultures oxidized glucose quantitatively to gluconic acid. However, during oxygen-limited growth on this mixture glucose was not oxidized and only very low levels of glucose dehydrogenase were detected in cell-free extracts. After introduction of excess oxygen, however, cultures or washed cell suspensions almost instantaneously gained the capacity to oxidize glucose at a high rate, by an as yet unknown mechanism.

The influence of the culture pH value on the direct glucose oxidative pathway in Klebsiella pneumoniae NCTC 418

Klebsiella pneumoniae NCTC 418 was cultured aerobically in chemostat cultures (D = 0.3 h-1; 35 degrees C) under respectively carbon-, phosphate-, potassium-, sulphate-, and ammonia-limited conditions with glucose as the sole carbon and energy source. The effect of the external pH value on glucose metabolism and on the enzymes of the direct glucose oxidative pathway was examined. The pH value of the medium had a profound influence on both the activity and the synthesis of the glucose dehydrogenase and the gluconate dehydrogenase. At pH values ranging from pH 5.5 to pH 6.0 maximal activity and synthesis of these enzymes resulted in a more than 80% conversion of the glucose consumed into gluconate and 2-ketogluconate under potassium- or phosphate-limited conditions. On the other hand, no gluconate and/or 2-ketogluconate production could be detected when K. pneumoniae was cultured at pH 8.0. Whereas the synthesis of gluconate dehydrogenase seemingly was completely repressed, still some glucose dehydrogenase was present. The lack of glucose dehydrogenase activity at pH 8.0 was shown not to be due to the dissociation of the cofactor PQQ from the enzyme.

The separate roles of PQQ and apo-enzyme syntheses in the regulation of glucose dehydrogenase activity in Klebsiella pneumoniae NCTC 418

No holoenzyme pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase and only very low apoenzyme levels could be detected in cells of Klebsiella pneumoniae, growing anaerobically, or carrying out a fumarate or nitrate respiration. Low glucose dehydrogenase activity in some aerobic glucose-excess cultures of K. pneumoniae (ammonia or sulphate limitation) was increased significantly by addition of PQQ, whereas in cells already possessing a high glucose dehydrogenase activity (phosphate or potassium limitation) extra PQQ had almost no effect. These observations indicate that the glucose dehydrogenase activity in K. pneumoniae is modulated by both PQQ synthesis and synthesis of the glucose dehydrogenase apo-enzyme.