Cloning of Escherichia coli lacZ and lacY genes and their expression in Gluconobacter oxydans and Acetobacter liquefaciens.
An efficient transformation protocol for Gluconobacter oxydans and Acetobacter liquefaciens strains was developed by preparation of electrocompetent cells grown on yeast extract-ethanol medium. Plasmid pBBR122 was used as broad-host-range vector to clone the Escherichia coli lacZY genes in G. oxydans and A. liquefaciens. Although both lac genes were functionally expressed in both acetic acid bacteria, only a few transformants were able to grow on lactose. However, this ability strictly depended on the presence of a plasmid expressing both lac genes. Mutations in the plasmids and/or in the chromosome were excluded as the cause of growth ability on lactose. (+info)
Novel enzymatic method for the production of xylitol from D-arabitol by Gluconobacter oxydans.
Microorganisms capable of producing xylitol from D-arabitol were screened for. Of the 420 strains tested, three bacteria, belonging to the genera Acetobacter and Gluconobacter, produced xylitol from D-arabitol when intact cells were used as the enzyme source. Among them, Gluconobacter oxydans ATCC 621 produced 29.2 g/l xylitol from 52.4 g/l D-arabitol after incubation for 27 h. The production of xylitol was increased by the addition of 5% (v/v) ethanol and 5 g/l D-glucose to the reaction mixture. Under these conditions, 51.4 g/l xylitol was obtained from 52.4 g/l D-arabitol, a yield of 98%, after incubation for 27 h. This conversion consisted of two successive reactions, conversion of D-arabitol to D-xylulose by a membrane-bound D-arabitol dehydrogenase, and conversion of D-xylulose to xylitol by a soluble NAD-dependent xylitol dehydrogenase. Use of disruptants of the membrane-bound alcohol dehydrogenase genes suggested that NADH was generated via NAD-dependent soluble alcohol dehydrogenase. (+info)
Construction of a vector plasmid for use in Gluconobacter oxydans.
A host vector system in Gluconobacter oxydans was constructed. An Acetobacter-Escherichia coli shuttle vector was introduced with the efficiency of 10(4) transformants/microg of DNA. Next, aiming for a self-cloning vector, we found a cryptic plasmid (which we named pAG5) of 5648 bp in G. oxydans strain IFO 3171, and sequenced the nucleotides. The plasmid seemed to have only one open reading flame (ORF) for a possible replication protein. Shuttle vectors of Gluconobacter-E. coli were constructed with the plasmid pAG5 and an E. coli vector, pUC18. (+info)
Transaldolase/glucose-6-phosphate isomerase bifunctional enzyme and ribulokinase as factors to increase xylitol production from D-arabitol in Gluconobacter oxydans.
Xylitol production from D-arabitol by the membrane and soluble fractions of Gluconobacter oxydans was investigated. Two proteins in the soluble fraction were found to have the ability to increase xylitol production. Both of these xylitol-increasing factors were purified, and on the basis of their NH(2)-terminal amino acid sequences the genes encoding both of the factors were cloned. Expression of the cloned genes in Escherichia coli showed that one of the xylitol-increasing factors is the bifunctional enzyme transaldolase/glucose-6-phosphate isomerase, and the other is ribulokinase. Using membrane and soluble fractions of G. oxydans, 3.8 g/l of xylitol were produced from 10 g/l D-arabitol after incubation for 40 h, and addition of purified recombinant transaldolase/glucose-6-phosphate isomerase or ribulokinase increased xylitol to 5.4 g/l respectively, confirming the identity of the xylitol-increasing factors. (+info)
Coenzyme specificity of enzymes in the oxidative pentose phosphate pathway of Gluconobacter oxydans.
The coenzyme specificity of enzymes in the oxidative pentose phosphate pathway of Gluconobacter oxydans was investigated. By investigation of the activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) in the soluble fraction of G. oxydans, and cloning and expression of genes in Escherichia coli, it was found that both G6PDH and 6PGDH have NAD/NADP dual coenzyme specificities. It was suggested that the pentose phosphate pathway is responsible for NADH regeneration in G. oxydans. (+info)
Purification and characterization of inducible cephalexin synthesizing enzyme in Gluconobacter oxydans.
Cephalexin synthesizing enzyme (CSE) of Gluconobacter oxydans ATCC 9324 was purified up to about 940-fold at a yield of 12%. CSE biosynthesis in G. oxydans was found inducible in the presence of D-phenylglycine but not its substrate phenylglycine methyl ester. The purified enzyme was shown homogeneous on SDS-PAGE and exhibited a specific activity of 440 U per mg protein. The apparent molecular mass of the native enzyme was estimated to be 70 kDa over a Superdex 200 gel filtration column and 68 kDa on SDS-PAGE, indicating that the native enzyme is a monomer. Its isoelectric focusing point is 7.1, indicating a neutral character. The enzyme had maximal activity around pH 6.0 to 6.5, and this activity was thermally stable up to 40 degrees C. Synthesis of cephalexin from D-phenylglycine methyl ester and 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) by the purified CSE was demonstrated. Its L-enantiomer was not accepted by CSE. Apart from cephalexin, ampicillin was also synthesized by the purified CSE from its acyl precursors and 6-aminopenicillanic acid (6-APA). Substrate specificity studies indicated that the enzyme required a free alpha amino group and an activated carboxyl group as a methyl ester of D-form phenylglycine. Interestingly, the purified enzyme did not catalyze hydrolysis of its products, e.g., cephalexin, cephradine, and ampicillin, in contrast to enzymes from other strains of Pseudomonadaceae. (+info)
Microbial production of L-ascorbic acid from D-sorbitol, L-sorbose, L-gulose, and L-sorbosone by Ketogulonicigenium vulgare DSM 4025.
Ketogulonicigenium vulgare DSM 4025, known as a 2-keto-L-gulonic acid producing strain from L-sorbose via L-sorbosone, surprisingly produced L-ascorbic acid from D-sorbitol, L-sorbose, L-gulose, and L-sorbosone as the substrate under a growing or resting condition. As the best result, K. vulgare DSM 4025 produced 1.37 g per liter of L-AA from 5.00 g per liter of L-sorbosone during 4 h incubation time at 30 degrees C under the resting cell condition having 5.70 g per liter of wet cells. The precursor of L-AA formation from D-sorbitol and L-sorbose, except for L-gulose, was thought to be the putative furanose form of L-sorbosone. This is the first time it is reported that bacteria can produce vitamin C via L-sorbosone. (+info)
Knockout and overexpression of pyrroloquinoline quinone biosynthetic genes in Gluconobacter oxydans 621H.
In Gluconobacter oxydans, pyrroloquinoline quinone (PQQ) serves as the cofactor for various membrane-bound dehydrogenases that oxidize sugars and alcohols in the periplasm. Proteins for the biosynthesis of PQQ are encoded by the pqqABCDE gene cluster. Our reverse transcription-PCR and promoter analysis data indicated that the pqqA promoter represents the only promoter within the pqqABCDE cluster of G. oxydans 621H. PQQ overproduction in G. oxydans was achieved by transformation with the plasmid-carried pqqA gene or the complete pqqABCDE cluster. A G. oxydans mutant unable to produce PQQ was obtained by site-directed disruption of the pqqA gene. In contrast to the wild-type strain, the pqqA mutant did not grow with d-mannitol, d-glucose, or glycerol as the sole energy source, showing that in G. oxydans 621H, PQQ is essential for growth with these substrates. Growth of the pqqA mutant, however, was found with d-gluconate as the energy source. The growth behavior of the pqqA mutant correlated with the presence or absence of the respective PQQ-dependent membrane-bound dehydrogenase activities, demonstrating the vital role of these enzymes in G. oxydans metabolism. A different PQQ-deficient mutant was generated by Tn5 transposon mutagenesis. This mutant showed a defect in a gene with high homology to the Escherichia coli tldD gene, which encodes a peptidase. Our results indicate that the tldD gene in G. oxydans 621H is involved in PQQ biosynthesis, possibly with a similar function to that of the pqqF genes found in other PQQ-synthesizing bacteria. (+info)