Growth on D-arabitol of a mutant strain of Escherichia coli K12 using a novel dehydrogenase and enzymes related to L-1,2-propanediol and D-xylose metabolism.

Escherichia coli K12 cannot grow on D-arabitol, L-arabitol, ribitol or xylitol (Reiner, 1975). Using a mutant of E. coli K12 (strain 3; Sridhara et al., 1969) that can grow on L-1,2-propanediol, a second-stage mutant was isolated which can utilize D-arabitol as sole source of carbon and energy for growth. D-Arabitol is probably transported into the bacteria by the same system as that used for the transport of L-1,2-propanediol. The second-stage mutant constitutively synthesizes a new dehydrogenase, which is not present in the parent strain 3. This enzyme, whose native substrate may be D-galactose, apparently dehydrogenates D-arabitol to D-xylulose, and its structural gene is located at 68.5 +/- 1 min on the E. coli genetic map. D-Xylulose is subsequently catabolized by the enzymes of the D-xylose metabolic pathway.     

Construction of intergeneric hybrids using bacteriophage P1CM: transfer of the Klebsiella aerogenes ribitol dehydrogenase gene to Escherichia coli.

Study of many of the interesting properties of Klebsiella aerogenes is limited by the lack of a well-characterized genetic system for this organism. Our investigations of the evolution of the enzyme ribitol dehydrogenase (EC 1.1.1.56) in K. aerogenes would be greatly facilitated by the availability of such a system, and we here report two approaches to developing one. We have isolated mutants sensitive to the coliphage P1, which will efficiently tranduce genetic markers between such sensitive strains and which will thus make detailed mapping studies possible. Derivatives of K. aerogenes lysogenic for P1 can be readily isolated by using the specialized transducing particle P1CMclr100. Bacteria lysogenic for this phage are chloramphenicol resistant and temperature sensitive. Phage particles produced by temperature induction of such lysogens can be used to transfer K. aerogenes genes to the natural host of P1 phage. Escherichia coli. We have used this method to prepare derivatives of E. coli K-12 carrying the K. aerogenes genes conferring the ability to metabolize the pentitols ribitol and D-arabitol. We have shown that these E. coli-K. aerogenes hybrids synthesize a ribitol dehydrogenase with the properties of the K. aerogenes enzyme and have mapped the position of the transferred gene on the E. coli chromosome. The ramifications of this methodology are discussed.     

The determination of lactate turnover in vivo with 3H- and 14C-labelled lactate. The significance of sites of tracer administration and sampling.

The D-ribulokinase and D-xylulokinase of Klebsiella aerogenes were purified to homogeneity from Escherichia coli K12 construct strains that synthesized these enzymes constitutively. The D-ribulokinase, which is encoded in the ribitol operon, is active as a dimer of 60 000 subunit mol.wt., whereas the D-xylulokinase, which is encoded in the D-arabitol operon, is active as a dimer of 54 000 subunit mol.wt. The amino acid compositions and N-terminal sequences of both pentulokinases are reported. The Kapp. values of the enzymes for their D-pentulose substrates were determined, and the D-ribulokinase was shown to have a low-affinity side-specificity for ribitol and D-arabitol. These results are discussed in the context of the evolution of the Klebsiella aerogenes pentitol operons.     

Directed evolution of a second xylitol catabolic pathway in Klebsiella pneumoniae.

Klebsiella pneumoniae PRL-R3 has inducible catabolic pathways for the degradation of ribitol and D-arabitol but cannot utilize xylitol as a growth substrate. A mutation in the rbtB regulatory gene of the ribitol operon permits the constitutive synthesis of the ribitol catabolic enzymes and allows growth on xylitol. The evolved xylitol catabolic pathway consists of an induced D-arabitol permease system that also transports xylitol, a constitutively synthesized ribitol dehydrogenase that oxidizes xylitol at the C-2 position to produce D-xylulose, and an induced D-xylulokinase from either the D-arabitol or D-xylose catabolic pathway. To investigate the potential of K. pneumoniae to evolve a different xylitol catabolic pathway, strains were constructed which were unable to synthesize ribitol dehydrogenase or either type of D-xylulokinase but constitutively synthesized the D-arabitol permease system. These strains had an inducible L-xylulokinase; therefore, the evolution of an enzyme which oxidized xylitol at the C-4 position to L-xylulose would establish a new xylitol catabolic pathway. Four independent xylitol-utilizing mutants were isolated, each of which had evolved a xylitol-4-dehydrogenase activity. The four dehydrogenases appeared to be identical because they comigrated during nondenaturing polyacrylamide gel electrophoresis. This novel xylitol dehydrogenase was constitutively synthesized, whereas L-xylulokinase remained inducible. Transductional analysis showed that the evolved dehydrogenase was not an altered ribitol or D-arabitol dehydrogenase and that the evolved dehydrogenase structural gene was not linked to the pentitol gene cluster. This evolved dehydrogenase had the highest activity with xylitol as a substrate, a Km for xylitol of 1.4 M, and a molecular weight of 43,000.     

Cloning of the xylitol dehydrogenase gene from Gluconobacter oxydans and improved production of xylitol from D-arabitol

Xylitol dehydrogenase (XDH) was purified from the cytoplasmic fraction of Gluconobacter oxydans ATCC 621. The purified enzyme reduced D-xylulose to xylitol in the presence of NADH with an optimum pH of around 5.0. Based on the determined NH2-terminal amino acid sequence, the gene encoding xdh was cloned, and its identity was confirmed by expression in Escherichia coli. The xdh gene encodes a polypeptide composed of 262 amino acid residues, with an estimated molecular mass of 27.8 kDa. The deduced amino acid sequence suggested that the enzyme belongs to the short-chain dehydrogenase/reductase family. Expression plasmids for the xdh gene were constructed and used to produce recombinant strains of G. oxydans that had up to 11-fold greater XDH activity than the wild-type strain. When used in the production of xylitol from D-arabitol under controlled aeration and pH conditions, the strain harboring the xdh expression plasmids produced 57 g/l xylitol from 225 g/l D-arabitol, whereas the control strain produced 27 g/l xylitol. These results demonstrated that increasing XDH activity in G. oxydans improved xylitol productivity.     

Purification and properties of a polyol dehydrogenase from the phototrophic bacterium Rhodobacter sphaeroides

A polyol dehydrogenase was detected in cell extracts of the facultative phototrophic bacterium Rhodobacter sphaeroides strain Si 4 grown on D-glucitol (sorbitol) as the sole carbon source. The enzyme was purified 150-fold to apparent homogeneity by steps involving fractionated (NH4)2SO4 precipitation, chromatography on Q-Sepharose and phenyl-Sepharose, and FPLC on Superose 12. The relative molecular mass (Mr) of the native polyol dehydrogenase was 47,200 as calculated from its Stokes' radius (rs = 2.76 nm) and sedimentation coefficient (s20, w = 4.15 S). SDS/PAGE resulted in one single band representing a polypeptide with a Mr of 52,200, indicating that the native protein is a monomer. The isoelectric point of the polyol dehydrogenase was determined to be pH 4.3. The enzyme was specific for NAD+ and oxidized both D-glucitol and D-mannitol to D-fructose, as well as D-arabinitol to D-ribulose. The pH optimum of substrate oxidation was pH 9.0 in 0.1 M Tris/HCl and that of substrate reduction was pH 6.5 in 0.1 M potassium phosphate. The reactions exhibited normal Michaelis-Menten kinetics allowing the estimation of KM values for NAD+ (0.18 mM) in the presence of D-glucitol, and for D-glucitol (31.8 mM), D-mannitol (0.29 mM) and D-arabinitol (1.8 mM), respectively. The KM value for D-fructose was 16.3 mM and that for NADH 0.02 mM. The equilibrium constants determined for the conversion of D-mannitol, D-glucitol and D-arabinitol were 4.5 nM, 0.58 nM and 80 pM, respectively. Based on the catalytic preference of the polyol dehydrogenase for D-mannitol, an enzymatic assay for D-mannitol was elaborated.     

An unstable small-colony variant of a noninvasive mutant of Salmonella typhimurium is highly invasive for MDCK cells

Abstract A sorbitol dehydrogenase was purified from the membrane fraction of Gluconobacter suboxydans KCTC 2111 (= ATCC 621) by chromatography on CM-, DEAE-, Mono S and Superose 12 columns. The purified enzyme showed a single activity band upon nondenaturing polyacrylamide gel electrophoresis (PAGE) and three subunits of 75, 50 and 14 kDa upon SDS-PAGE. When purified preparations of the enzyme were reconstituted with pyrroloquinoline quinone (PQQ), the specific enzyme activity was significantly increased (up to 9-fold). The absorption spectrum of purified sorbitol dehydrogenase in the reduced state exhibited three absorption maxima (417, 522 and 552 nm) which is in accordance with the typical absorption spectrum of cytochrome c . The 50 kDa subunit appeared as a red band on unstained SDS-gels suggesting its identity as a cytochrome. Fluorescence spectra of extracts from purified sorbitol dehydrogenase showed an excitation maximum at 370 nm and an emission maximum at 465 nm, which conformed to those of authentic PQQ. The purified enzyme showed a rather broad substrate specificity with significant activity toward D-mannitol (68%) and D-ribitol (70%) as well as D-sorbitol (100%). The PQQ-dependent sorbitol dehydrogenase described in this study is clearly different from the FAD-dependent sorbitol dehydrogenase from G. suboxydans var. α IFO 3254 strain in its cofactor requirement and substrate specificity.     

Polyol metabolism by Rhizobium trifolii.

In Rhizobium trifolii 7000, the polyols myo-inositol, xylitol, ribitol, D-arabitol, D-mannitol, D-sorbital, and dulcitol are metabolized by inducible nicotinamide adenine dinucleotide-dependent polyol dehydrogenases. Five different polyol dehydrogenases were recognized: inositol dehydrogenase, specific for inositil; ribitol dehydrogenase, specific for ribitol; D-arabitol dehydrogenase, which oxidized D-arabitol, D-mannitol, and D-sorbitol; xylitol dehydrogenase, which oxidized xylitol and D-sorbitol; and dulcitol dehydrogenase, which oxidized dulcitol, ribitol, xylitol, and sorbitol. Apart from inositil and xylitol, all of the polyols induced more than one polyol dehydrogenase and polyol transport system, but the heterologous polyol dehydrogenases and polyol transport systems were not coordinately induced by a particular polyol. With the exception of xylitol, all of the polyols tested served as growth substrates. A mutant of trifolii 7000, which was constitutive for dulcitol dehydrogenase, could also grow on xylitol.     

Biosynthesis and catabolism of 6-deoxy L-talitol by Klebsiella aerogenes mutants.

A mutant strain of Klebsiella aerogenes was constructed and, when incubated anaerobically with L-fucose and glycerol, synthesized and excreted a novel methyl pentitol, 6-deoxy L-talitol. The mutant was constitutive for the synthesis of L-fucose isomerase but unable to synthesize L-fuculokinase activity. Thus, it could convert the L-fucose to L-fuculose but was incapable of phosphorylating L-fuculose to L-fuculose 1-phosphate. The mutant was also constitutive for the synthesis of ribitol dehydrogenase, and in the presence of sufficient reducing power this latter enzyme catalyzed the reduction of the L-fuculose to 6-deoxy L-talitol. The reducing equivalents required for this reaction were generated by the oxidation of glycerol to dihydroxyacetone with an anaerobic glycerol dehydrogenase. The parent strain of K. aerogenes was unable to utilize the purified 6-deoxy L-talitol as a sole source of carbon and energy for growth; however, mutant could be isolated which had gained this ability. Such mutants were found to be constitutive for the synthesis of ribitol dehydrogenase and were thus capable of oxidizing 6-deoxy L-talitol to L-fuculose. Further metabolism of L-fuculose was shown by mutant analysis to be mediated by the enzymes of the L-fucose catabolic pathway.     

Isolation of the aspartokinase domain of bifunctional aspartokinase I-homoserine dehydrogenase I from E.coli K12

A proteolytic fragment (Mr approximately 25 000) carrying only the aspartokinase activity has been purified by chromatofocusing after limited proteolysis of aspartokinase I-homoserine dehydrogenase I from E.coli K12. The NH2-terminal sequence shows that it corresponds to the amino terminal peptide of the native enzyme. The results confirm a previous hypothesis about the organization of native aspartokinase I-homoserine dehydrogenase I.     

Sequence of a secondary phage lambda attachment site located between the pentitol operons of Klebsiella aerogenes.

We have determined the nucleotide sequence of a secondary phage lambda attachment site (att) located between the structural genes of the ribitol and D-arabitol catabolic operons of Klebsiella aerogenes. The core region of this secondary attachment site (sequence: GGTTTTTTCGATTAT) shows considerable homology with the 15-base-pair core region common to both the phage att and the primary bacterial att of Escherichia coli K12 (sequence: GCTTTTTTACTAA); however, there is no such clear homology between the sequences flanking the cores of the primary att and this secondary att. Integration of phage lambda into the K. aerogenes secondary att occurred by recombination between the core region of the phage att and an oligo(T.A) stretch located within the K. aerogenes secondary att.     

Genetic mapping of tyramine oxidase and arylsulfatase genes and their regulation in intergeneric hybrids of enteric bacteria.

The genes for arylsulfatase (atsA) and tyramine oxidase (tynA) have been mapped in Klebsiella aerogenes by P1 transduction. They are linked to gdhD and trp in the order atsA-tynA-gdhD-trp-pyrF. Complementation analysis using F' episomes from Escherichia coli suggested an analogous location of these genes in E. coli, although arylsulfatase activity was not detected in E. coli. P1 phage and F' episomes were used to create intergeneric hybrid strains of enteric bacteria by transfer of the ats and tyn genes between K. aerogenes, E. coli, and Salmonella typhimurium. Intergeneric transduction of the tynK gene from K. aerogenes to an E. coli restrictionless strain was one to two orders less frequent than that of the leuK gene. The tyramine oxidase of E. coli and S. typhimurium in regulatory activity resemble very closely the enzyme of K. aerogenes. The atsE gene from E. coli was expressed, and latent arylsulfatase protein was formed in K. aerogenes and S typhimurium. The results of tyramine oxidase and arylsulfatase synthesis in intergeneric hybrids of enteric bacteria suggest that the system for regulation of enzyme synthesis is conserved more than the structure or function of enzyme protein during evolution.     

5-keto-D-gluconate production is catalyzed by a quinoprotein glycerol dehydrogenase,major polyol dehydrogenase,in gluconobacter species

Acetic acid bacteria, especially Gluconobacter species, have been known to catalyze the extensive oxidation of sugar alcohols (polyols) such as D-mannitol, glycerol, D-sorbitol, and so on. Gluconobacter species also oxidize sugars and sugar acids and uniquely accumulate two different keto-D-gluconates, 2-keto-D-gluconate and 5-keto-D-gluconate, in the culture medium by the oxidation of D-gluconate. However, there are still many controversies regarding their enzyme systems, especially on D-sorbitol and also D-gluconate oxidations. Recently, pyrroloquinoline quinone-dependent quinoprotein D-arabitol dehydrogenase and D-sorbitol dehydrogenase have been purified from G. suboxydans, both of which have similar and broad substrate specificity towards several different polyols. In this study, both quinoproteins were shown to be identical based on their immuno-cross-reactivity and also on gene disruption and were suggested to be the same as the previously isolated glycerol dehydrogenase (EC 1.1.99.22). Thus, glycerol dehydrogenase is the major polyol dehydrogenase involved in the oxidation of almost all sugar alcohols in Gluconobacter sp. In addition, the so-called quinoprotein glycerol dehydrogenase was also uniquely shown to oxidize D-gluconate, which was completely different from flavoprotein D-gluconate dehydrogenase (EC 1.1.99.3), which is involved in the production of 2-keto-D-gluconate. The gene disruption experiment and the reconstitution system of the purified enzyme in this study clearly showed that the production of 5-keto-D-gluconate in G. suboxydans is solely dependent on the quinoprotein glycerol dehydrogenase.     

利用代谢工程构建D-甘露醇生产菌株

D-甘露醇广泛应用于食品、制药、化学品工业等领域。从野生型大肠杆菌出发,将来自假肠膜明串珠菌Leuconostoc pseudomesenteroides ATCC 12291菌株的甘露醇脱氢酶与果糖转运蛋白编码基因整合到大肠杆菌ATCC 8739的染色体中,并失活其他的发酵途径 (丙酮酸甲酸裂解酶、乳酸脱氢酶、富马酸还原酶、乙醇脱氢酶、甲基乙二醛合成酶和丙酮酸氧化酶) ,构建了一株遗传稳定的D-甘露醇生产菌株。使用无机盐培养基和葡萄糖果糖作为混合碳源,厌氧发酵6 d,D-甘露醇产量达1.2 mmol/L。基于细胞生长和D-甘露醇合成的偶联,进一步通过代谢进化技术提高细胞合成D-甘露醇的生产能力。经过80代的驯化,D-甘露醇产量提高了2.6倍,甘露醇脱氢酶的活性提高了2.8倍。构建获得的遗传稳定的工程菌能直接发酵糖生产D-甘露醇,不需添加抗生素、诱导剂和甲酸,在工业化生产时有一定优势。     

IMP dehydrogenase. II. Purification and properties of the enzyme from Yoshida sarcoma ascites tumor cells

The preceding paper showed that IMP dehydrogenase [IMP:NAD+ oxidoreductase, EC 1.2.1.14] tended to form a precipitable complex(es) through ionic and hydrophobic interactions. On the basis of these observations, a method was developed for purification of IMP dehydrogenase from Yoshida sarcoma ascites cells. On SDS-polyacrylamide gel electrophoresis, the purified preparation (1.19 U/mg protein) appeared homogeneous and its minimum molecular weight was estimated to be 68K daltons. Amino acid analyses indicated a subunit molecular weight of 68,042. Molecular sieve chromatography in the presence of 10% (NH4)2SO4 showed that the molecular weight of the native enzyme was 127K daltons. These values indicate that the native enzyme is composed of two identical subunits. However, the purified enzyme gave 4 protein bands on polyacrylamide gel electrophoresis under non-denaturing conditions, and appeared as a single fraction in the vicinity of the void volume on Ultrogel AcA 34 column chromatography at low salt concentration, indicating that its molecular weight exceeded 200K daltons. These findings indicate that the enzyme tends to aggregate owing to its own physicochemical characteristics. The Km values for IMP and NAD were calculated to be 12 and 25 microM, respectively, and the Ki values for XMP, GMP, and AMP to be 109, 130, and 854 microM, respectively. The purified enzyme showed full activity in the presence of K+, and K+ could be partially replaced by Na+. PCMB inactivated the enzyme, but the activity was completely restored by the addition of DTT. Cl-IMP also inactivated the enzyme and IMP prevented this inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Production of D- and L-xylulose by mutants of Klebsiella pneumoniae and Erwinia uredovora

D-Xylulose and L-xylulose were produced biologically by the oxidation of a corresponding pentitol. A Klebsiella pneumoniae mutant was constructed for the oxidation of D-arabitol to D-xylulose. This mutant constitutively synthesized the D-arabitol permease system and D-arabitol dehydrogenase but was unable to produce the D-xylulokinase of the D-arabitol pathway or the D-xylose isomerase and D-xylulokinase of the D-xylose pathway. An Erwinia uredovora mutant which constitutively synthesized a novel xylitol-4-dehydrogenase but could not synthesize L-xylulokinase was used for the oxidation of xylitol to L-xylulose. Washed cell suspensions of either mutant incubated with 0.5% pentitol would oxidize 60 to 65% of the pentitol to the corresponding ketopentose in 18 h and excrete the ketopentose into the medium. Ketopentoses were rapidly purified from the remaining pentitol by hydroxyl affinity chromatography.     

Production of D- and L-xylulose by mutants of Klebsiella pneumoniae and Erwinia uredovora.

D-Xylulose and L-xylulose were produced biologically by the oxidation of a corresponding pentitol. A Klebsiella pneumoniae mutant was constructed for the oxidation of D-arabitol to D-xylulose. This mutant constitutively synthesized the D-arabitol permease system and D-arabitol dehydrogenase but was unable to produce the D-xylulokinase of the D-arabitol pathway or the D-xylose isomerase and D-xylulokinase of the D-xylose pathway. An Erwinia uredovora mutant which constitutively synthesized a novel xylitol-4-dehydrogenase but could not synthesize L-xylulokinase was used for the oxidation of xylitol to L-xylulose. Washed cell suspensions of either mutant incubated with 0.5% pentitol would oxidize 60 to 65% of the pentitol to the corresponding ketopentose in 18 h and excrete the ketopentose into the medium. Ketopentoses were rapidly purified from the remaining pentitol by hydroxyl affinity chromatography.     

Cloning of the pullulanase gene and overproduction of pullulanase in Escherichia coli and Klebsiella aerogenes

The pullulanase gene (pul) of Klebsiella aerogenes was cloned into a pBR322 vector in Escherichia coli. Deletion analysis of the recombinant plasmid showed that the pul coding sequence, probably with the regulator gene, was located entirely within a 4.2-kilobase segment derived from the chromosomal DNA of K. aerogenes. E. coli cells carrying the recombinant plasmids produced about three- to sevenfold more pullulanase than did the wild-type strain of K. aerogenes W70. When the cloned cells of E. coli were grown with pullulan or maltose, most pullulanase was produced intracellularly, whereas K. aerogenes produced pullulanase extracellularly. Transfer of the plasmid containing the pul gene into K. aerogenes W70 resulted in about a 20- to 40-fold increase in total production of pullulanase, and the intracellular enzyme level was about 100- to 150-fold higher than that of the parent strain W70. The high level of pullulanase activity in K. aerogenes cells carrying the recombinant plasmid was maintained for at least 2 weeks.     

Cloning of the pullulanase gene and overproduction of pullulanase in Escherichia coli and Klebsiella aerogenes.

The pullulanase gene (pul) of Klebsiella aerogenes was cloned into a pBR322 vector in Escherichia coli. Deletion analysis of the recombinant plasmid showed that the pul coding sequence, probably with the regulator gene, was located entirely within a 4.2-kilobase segment derived from the chromosomal DNA of K. aerogenes. E. coli cells carrying the recombinant plasmids produced about three- to sevenfold more pullulanase than did the wild-type strain of K. aerogenes W70. When the cloned cells of E. coli were grown with pullulan or maltose, most pullulanase was produced intracellularly, whereas K. aerogenes produced pullulanase extracellularly. Transfer of the plasmid containing the pul gene into K. aerogenes W70 resulted in about a 20- to 40-fold increase in total production of pullulanase, and the intracellular enzyme level was about 100- to 150-fold higher than that of the parent strain W70. The high level of pullulanase activity in K. aerogenes cells carrying the recombinant plasmid was maintained for at least 2 weeks.