Nitrogenase of Klebsiella pneumoniae nifV mutants.

The MoFe protein of nitrogenase from Klebsiella pneumoniae nifV mutants, NifV- Kp1 protein, in combination with the Fe protein from wild-type cells, catalysed CO-sensitive H2 evolution, in contrast with the CO-insensitive reaction catalysed by the wild-type enzyme. The decrease in H2 production was accompanied by a stoicheiometric decrease in dithionite (reductant) utilization, implying that CO was not reduced. However, CO did not affect the rate of phosphate release from ATP. Therefore the ATP/2e ratio increased, indicating futile cycling of electrons between the Fe protein and the MoFe protein. The inhibition of H2 evolution by CO was partial; it increased from 40% at pH6.3 to 82% at pH 8.6. Inhibition at pH7.4 (maximum 73%) was half-maximal at 3.1 Pa (0.031 matm) CO. The pH optimum of the mutant enzyme was lower in the presence of CO. Steady-state kinetic analysis of acetylene reduction indicated that CO was a linear, intersecting, non-competitive inhibitor of acetylene reduction with Kii = 2.5 Pa and Kis = 9.5 Pa. This may indicate that a single high-affinity CO-binding site in the NifV- Kp1 protein can cause both partial inhibition of H2 evolution and total elimination of acetylene reduction. Various models to explain the data are discussed.     

Isolation and characterization of lambda specialized transducing bacteriophages carrying Klebsiella pneumoniae nif genes

Seve lambda dnif specialized transducing bacteriophages were isolated from Escherichia coli strains containing plasmids carrying the his-nif region of Klebsiella pneumoniae. These phages collectively carry deoxyribonucleic acid for all of the genes in the nif regulon and adjacent deoxyribonucleic acid of K. pneumoniae. The phages were isolated by using Mu insertions in the nif region to direct the integration of lambda pMu phages in nif via formation of lambda pMu-Mu dilysogens which, upon induction, yielded lambda dnif phages. This procedure should be generally applicable for isolating lambda specialized transducing phages carrying genes from E. coli or other bacteria.     

Isolation and characterization of a protein-tyrosine kinase and a phosphotyrosine-protein phosphatase from Klebsiella pneumoniae

Two proteins of Klebsiella pneumoniae, termed Yor5 and Yco6, were analyzed for their capacity to participate in the reversible phosphorylation of proteins on tyrosine. First, protein Yco6 was overproduced from its specific gene and purified to homogeneity by affinity chromatography. Upon incubation in the presence of radioactive adenosine triphosphate, it was found to effectively autophosphorylate. Two-dimensional analysis of its phosphoamino acid content revealed that it was modified exclusively at tyrosine. Second, protein Yor5 was also overproduced from the corresponding gene and purified to homogeneity by affinity chromatography. It was shown to contain a phosphatase activity capable of cleaving the synthetic substrate p-nitrophenyl phosphate into p-nitrophenol and free phosphate. In addition, it was assayed on individual phosphorylated amino acids and appeared to dephosphorylate specifically phosphotyrosine, with no effect on phosphoserine or phosphothreonine. Such specificity for phosphotyrosine was confirmed by the observation that Yor5 was able to dephosphorylate protein Yco6 previously autophosphorylated. Together, these data demonstrate that similarly to other bacterial species including Acinetobacter johnsonii and Escherichia coli, the cells of K. pneumoniae contain both a protein-tyrosine kinase and a phosphotyrosine-protein phosphatase. They also provide evidence that this phosphatase can utilize the kinase as an endogenous substrate, which suggests the occurrence of a regulatory mechanism connected with reversible protein phosphorylation on tyrosine. Since Yco6 and Yor5 are both involved in the synthesis of capsular polysaccharide and since capsules are essential to the virulence of K. pneumoniae, we suggest that reversible protein phosphorylation on tyrosine may be part of the cascade of reactions that determine the pathogenicity of bacteria.     

Isolation and characteristics of Klebsiella pneumoniae lysozyme factor

For the first time the preparation of K. pneumoniae antilysozyme factor has been isolated and purified. This factor, having a molecular weight of about 1,000 daltons, is oligopeptide with an oligosaccharide part. It also contains such amino acids as proline, lysine, arginine and tyrosine. The antilysozyme factor is resistant to 30-minute boiling and has no optimal pH value for its action.     

Isolation and Characterisation of Lytic Bacteriophages of Klebsiella pneumoniae and Klebsiella oxytoca

Klebsiella bacteria have emerged as an increasingly important cause of community-acquired nosocomial infections. Extensive use of broad-spectrum antibiotics in hospitalised patients has led to both increased carriage of Klebsiella and the development of multidrug-resistant strains that frequently produce extended-spectrum β-lactamases and/or other defences against antibiotics. Many of these strains are highly virulent and exhibit a strong propensity to spread. In this study, six lytic Klebsiella bacteriophages were isolated from sewage-contaminated river water in Georgia and characterised as phage therapy candidates. Two of the phages were investigated in greater detail. Biological properties, including phage morphology, nucleic acid composition, host range, growth phenotype, and thermal and pH stability were studied for all six phages. Limited sample sequencing was performed to define the phylogeny of the K. pneumoniae- and K. oxytoca-specific bacteriophages vB_Klp_5 and vB_Klox_2, respectively. Both of the latter phages had large burst sizes, efficient rates of adsorption and were stable under different adverse conditions. Phages reported in this study are double-stranded DNA bacterial viruses belonging to the families Podoviridae and Siphoviridae. One or more of the six phages was capable of efficiently lysing ~63 % of Klebsiella strains comprising a collection of 123 clinical isolates from Georgia and the United Kingdom. These phages exhibit a number of properties indicative of potential utility in phage therapy cocktails.     

Purification and characterization of Klebsiella pneumoniae cytotoxins.

Isolation, purification and characterization of 3 new cytotoxins of a K. pneumoniae strain isolated from ready to eat pork sausage are reported. Purification process involved extraction of cytotoxins with polymyxin B sulphate, salt precipitation, gel filtration and anion exchange chromatography. Klebsiella cytotoxin (KCT) I, a glycoprotein of about 65 kDa was verocytotoxic, enterotoxic and dermonerotic. KCT II was erythemogenic, verocytotoxic and enterotoxic protein of co 55 kDa, while KCT III was about double in MW (110 kDa) hadverocytotoxicity but neither enterotoxicity nor dermatotoxicity. KCT I and II caused granulation, conglomeration, shrinkage, detachment and lysis of MDBK and Vero cells, while KCT III induced enlargement, vacuolation, granulation, multinucleolation and syncytia formation in exposed cells. All the three cytotoxins induced specific neutralizing antibodies and cytotoxins were detectable in nanogram quantities with enzyme-linked immunosorbant assay using homologous antibodies. None of the anticytotoxin cross-reacted with either heterologous Klebsiella cytotoxins or with verocytotoxic preparations of Shigella dysenteriae.     

Kinetics of ethanolic fermentation of D-xylose by Klebsiella pneumoniae and its mutants

The microbial production of ethanol from D-xylose by a new soil isolate of Klebsiella pneumoniae and the mutants K. pneumoniae MB-16 and MB-16-1048 was studied. Kinetic and physiological properties of the mutants were compared with those of the original isolate. The volumetric rates of ethanol formation by mutants MB-16-1048 and MB-16 and the original isolate were 1.58, 0.50, and 0.06 g liter-1 h-1, respectively. The cultivation times of mutants MB-16-1048 and MB-16 were 20 and 18 h, respectively, and that of the original isolate was 118 h. Both the mutants exhibited metabolic similarities with the original isolate. Ethanol was the major end product of fermentation in all three strains. Acetic acid and carbon dioxide were the other two important by-products of fermentation. Pyruvic acid was accumulated in significant proportions as an intermediate. The proportion of pyruvate in the original isolate was 54% of the total D-xylose utilized, whereas for MB-16 and MB-16-1048 the values were about 42 and 22%, respectively. The lower fractions of pyruvate in mutants MB-16 and MB-16-1048 showed up as a 41 and 82% improvement, respectively, over the original isolate in terms of the ethanol yield.     

Isolation and characterization ofPhaffia rhodozyma mutants

Mutagenic treatment with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) inPhaffia rhodozyma generated 15 mutants with a wide diversity of color variants ranging from white to dark red. Characterization of the mutants by absorption spectra, TLC and HPLC was performed. Two categories could be distinguished: astaxanthin hyperproducing and astaxanthin hypoproducing mutants. Hyperproducing mutants exhibited considerable increases in astaxanthin content whereas hypoproducing mutants showed higher β-carotene contents than the wild-type strain. The characterization of carotenoid mutants inP. rhodozyma could contribute to the knowledge of the biosynthetic pathway of astaxanthin production of this microorganism.     

Regulation of nitrogen fixation. Nitrogenase-derepressed mutants of Klebsiella pneumoniae.

1. A new procedure is described for selecting nitrogenase-derepressed mutants based on the method of Brenchley et al. (Brenchley, J.E., Prival, M.J. and Magasanik, B. (1973) J. Biol. Chem. 248, 6122-6128) for isolating histidase-constitutive mutants of a non-N2-fixing bacterium. 2. Nitrogenase levels of the new mutants in the presence of NH4+ were as high as 100% of the nitrogenase activity detected in the absence of NH4+. 3. Biochemical characterization of these nitrogen fixation (nif) derepressed mutants reveals that they fall into three classes. Three mutants (strains SK-24, 28 and 29), requiring glutamate for growth, synthesize nitrogenase and glutamine synthetase constitutively (in the presence of NH4+). A second class of mutants (strains SK-27 and 37) requiring glutamine for growth produces derepressed levels of nitrogenase activity and synthesized catalytically inactive glutamine synthetase protein, as determined immunologically. A third class of glutamine-requiring, nitrogenase-derepressed mutants (strain SK-25 and 26) synthesizes neither a catalytically active glutamine synthetase enzyme nor an immunologically cross-reactive glutamine synthetase protein. 4. F-prime complementation analysis reveals that the mutant strains SK-25, 26, 27, 37 map in a segment of the Klebsiella chromosome corresponding to the region coding for glutamine synthetase. Since the mutant strains SK-27 and SK-37 produce inactive glutamine synthetase protein, it is concluded that these mutations map within the glutamine synthetase structural gene.     

Complementation analysis of Klebsiella pneumoniae mutants defective in nitrogen fixation.

Summary A series of mutants defective in nitrogen fixation (nif) were isolated in Klebsiella pneunoniae strain M5a1. The nif mutations were either located on plasmid pRD1 or on the K. pneumoniae chromosome. A total of 37 plasmid mutants and 28 chromosomal mutants were employed in complementation tests using the acetylene reduction technique. Most mutants could be assigned to one of seven nif cistrons: nifA, nifB, nifD, nifE, nifF, nifH, and nifK.Complementation analysis of two nif deletion mutants confirmed transductional evidence that these strains carry nifB-A-F deletions. One deletion mutant had, in contrast to previous transductional analysis, a functional nifK cistron and presumably is deleted for nifB-A-F-E.Examination of the biochemical phenotype of several mutants suggests that the nifA product has a regulatory function, and nifK, nifD and nifH are most probably the structural genes for nitrogenase.     

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.     

Molecular weight determination and partial characterization of Klebsiella pneumoniae hemolysins

Two thiol-activated Klebsiella pneumoniae hemolysins were purified from growth media by means of salt precipitation, gel filtration, ion-exchange chromatography, and polyacrylamide gel electrophoresis. The hemolysins peaks coincided with the protein and glycoprotein peaks as determined by chromatography and electrophoresis. The molecular weights, estimated by gel filtration, were 8400 and 19,000; by sodium dodecyl sulfate--polyacrylamide gel electrophoresis, the values were calculated as 15,500 and 27,000. The electrophoretic bands were best detected by the periodic acid--Schiff method. Reduction of the disulfide linkages did not cause the originally larger molecule to break into 8400 and 19,000 hemolysins. However, trypsin treatment cleaved the 19,000 hemolysin into an active moiety, with an electrophoretic migration similar to the 8400 hemolysin. A naturally occurring proteolytic activity was investigated using pepstatin and antipain. When the trypsin inhibitor was added to the system, the hemolytic activity was detected only in the 19,000 hemolysin and the smaller hemolysin was absent.     

Purification and characterization of a bacteriocin from Klebsiella pneumoniae 158

Klebocin, a bacteriocin produced by Klebsiella pneumoniae 158, was purified to homogeneity by ammonium sulphate fractionation and sequential DEAE-Sephacel and Sephadex G-150 column chromatography. The purified preparation had an Mr of approximately 40 000 on SDS-PAGE. Chemical analysis of the purified preparation showed it to be a protein, and it was sensitive to digestion by various proteolytic enzymes.     

耐盐氨基甲酸乙酯水解酶的分离纯化及酶学性质

氨基甲酸乙酯是发酵食品中存在的一种致癌物质,酶法去除发酵食品中的氨基甲酸乙酯是消除氨基甲酸乙酯危害的一种重要方法。从小鼠的胃部获得了一株产氨基甲酸乙酯水解酶的肺炎克雷伯氏菌,为了解该氨基甲酸乙酯水解酶的酶学性质,从肺炎克雷伯氏菌中提取获得氨基甲酸乙酯水解酶粗酶液,经硫酸铵沉淀、离子交换层析和凝胶过滤层析分离得到氨基甲酸乙酯水解酶纯酶。通过十二烷基硫酸钠聚丙烯酰胺电泳(SDS-PAGE)分析,估计该酶的分子量约为55 kDa。其水解氨基甲酸乙酯的Km值为74 mmol/L。酶反应的最适温度为55℃,最适pH为7.0。乙二胺四乙酸(EDTA)和二硫苏糖醇(DTT)对该酶有较强的激活作用,而Cu2+和Zn2+则有较强的抑制作用。该酶可耐受高浓度NaCl,对低浓度乙醇也有一定的耐受性,对于酱油中氨基甲酸乙酯的消除有一定的参考意义。