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Query: UMLS:C0519030 (Klebsiella)
 21,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Gram-negative bacteria (n = 192) isolated from infected bovine mammary glands were tested for growth in a pooled source of dry cow secretion. Growth of Klebsiella pneumoniae in dry cow secretion was greater than growth of Escherichia coli and Klebsiella oxytoca. Escherichia coli originating during the early dry period exhibited greater growth in dry cow secretion than those originating around calving or during lactation. Klebsiella pneumoniae growth did not differ with time of origin of intramammary infection. Escherichia coli, K. oxytoca, and K. pneumoniae growth in a synthetic medium was reduced by apolactoferrin plus Ig. Growth reduction was greatest for E. coli. Citrate reversed growth inhibition. The inhibitory properties of dry cow secretion for E. coli may contribute to the low number of naturally occurring intramammary infections originating during the early part of the dry period. Inhibitory properties of dry cow secretion are partially explained by lactoferrin acting in conjunction with antibody to prevent iron acquisition by many gram-negative bacteria.
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PMID:Growth of gram-negative bacteria in dry cow secretion. 218 75

A binary plasmid system was used to produce nitrogenase components in Escherichia coli and subsequently to define a minimum set of nitrogen fixation (nif) genes required for the production of the iron-molybdenum cofactor (FeMoco) reactivatable apomolybdenum-iron (apoMoFe) protein of nitrogenase. The active MoFe protein is an alpha 2 beta 2 tetramer containing two FeMoco clusters and 4 Fe4S4 P centers (for review see, Orme-Johnson, W.H. (1985) Annu. Rev. Biophys. Biophys. Chem. 14, 419-459). The plasmid pVL15, carrying a tac-promoted nifA activator gene, was coharbored in E. coli with the plasmid pGH1 which contained nifHDKTYENXUSVWZMF' derived from the chromosome of the nitrogen fixing bacterium Klebsiella pneumoniae. The apoMoFe protein produced in E. coli by pGH1 + VL15 was identical to the apoprotein in derepressed cells of the nifB- mutant of K. pneumoniae (UN106) in its electrophoretic properties on nondenaturing polyacrylamide gels as well as in its ability to be activated by FeMoco. The constituent peptides migrated identically to those from purified MoFe protein during electrophoresis on denaturing gels. The concentrations of apoMoFe protein produced in nif-transformed strains of E. coli were greater than 50% of the levels of MoFe protein observed in derepressed wild-type K. pneumoniae. Systematic deletion of individual nif genes carried by pGH1 has established the requirements for the maximal production of the FeMoco-reactivatable apoMoFe protein to be the following gene products, NifHDKTYUSWZM+A. It appears that several of the genes (nifT, Y, U, W, and Z) are only required for maximal production of the apoMoFe protein, while others (nifH, D, K, and S) are absolutely required for synthesis of this protein in E. coli. One curious result is that the nifH gene product, the peptide of the Fe protein, but not active Fe protein itself, is required for formation of the apoMoFe protein. This suggests the possibility of a ternary complex of the NifH, D, and K peptides as the substrate for the processing to form the apoMoFe protein. We also find that nifM, the gene which processes the nifH protein into Fe protein (Howard, K.S., McLean, P.A., Hansen, F. B., Lemley, P.V., Kobla, K.S. & Orme-Johnson, W.H. (1986) J. Biol. Chem. 261, 772-778) can, under certain circumstances, partially replace other processing genes (i.e. nifTYU and/or WZ) although it is not essential for apoMoFe protein formation. It also appears that nifS and nifU, reported to play a role in Fe protein production in Azotobacter vinelandii, play no such role in K. pneumoniae, although these genes are involved in apoMoFe formation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Genes required for formation of the apoMoFe protein of Klebsiella pneumoniae nitrogenase in Escherichia coli. 220 91

The in vitro synthesis of the iron-molybdenum cofactor nitrogenase was inhibited by a low-molecular-weight factor. This inhibitory factor was present in the membrane extracts of wild-type and nif mutant strains of Klebsiella pneumoniae that were grown under conditions that either repressed or derepressed nitrogenase expression. In vitro, the inhibition was specific for the NifB protein. Addition of this factor to K. pneumoniae cells at various times during nif derepression decreased nitrogenase activity, presumably through inhibition of iron-molybdenum cofactor synthesis. The inhibitor was purified by solvent extraction and chromatography on DEAE-cellulose, silica gel, and aluminum oxide columns.
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PMID:Synthesis of the iron-molybdenum cofactor of nitrogenase is inhibited by a low-molecular-weight metabolite of Klebsiella pneumoniae. 221 26

Iron K-edge e.x.a.f.s. data for the iron-vanadium cofactor (FeVaco) from Azotobacter chroococcum vanadium nitrogenase reported here provide further evidence for the structural similarity between this and the iron-molybdenum nitrogenase cofactor (FeMoco) from Klebsiella pneumoniae molybdenum nitrogenase [Arber, Flood, Garner, Gormal, Hasnain & Smith (1988) Biochem. J. 252, 421-425]. The e.x.a.f.s. data are consistent with the vanadium being present in a V-Fe-S cluster, thus confirming that the N-methylformamide extract of the VFe protein component of A. chroococcum vanadium nitrogenase does indeed contain a polynuclear metal-sulphur cluster. Additionally, a long Fe-Fe distance is observed as 0.369 nm, demonstrating the presence of a long-range order in the cluster.
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PMID:Iron K-edge X-ray-absorption spectroscopy of the iron-vanadium cofactor of the vanadium nitrogenase from Azotobacter chroococcum. 232 76

Several Klebsiella pneumoniae strains which produced enterochelin but not aerobactin were nevertheless sensitive to cloacin DF13. In contrast, a strain of serotype K1:O1 which produced both siderophores was cloacin-resistant. Loss by mutation of the O1 but not K1 antigen rendered this strain cloacin-sensitive, indicating that the O1 antigen prevented access of cloacin to the cloacin/aerobactin receptor. Unlike the K1:O1 strain, the aerobactin-negative strains failed to hybridize in a colony blot assay with an aerobactin receptor gene probe prepared from pColV-K30. However, antisera raised against the 74 kDa pColV-K30 aerobactin receptor cross-reacted with a 76 kDa outer-membrane protein in each K. pneumoniae strain. In addition to the 76 kDa protein, the K1:O1 strain also produced a strongly cross-reacting 74 kDa protein. To determine whether these aerobactin-negative strains could use aerobactin, mutants unable to synthesize siderophores were isolated. Aerobactin promoted the growth of these mutants in iron-deficient media. The evidence presented suggests that some K. pneumoniae strains produce an aerobactin iron-uptake system without apparent production of aerobactin and which is probably based on a 76 kDa receptor, the gene for which does not hybridize with aerobactin receptor gene encoded on pColV-K30.
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PMID:Novel aerobactin receptor in Klebsiella pneumoniae. 253 99

Three new Tn5-mutagenized nif genes of Azospirillum brasilense were characterized. The sizes of the restriction fragments and the restriction maps of the cloned nif DNA regions showed that these nif genes are distinct from those reported earlier, e.g. nifHDK, nifE, nifUS, fixABC. The Nif27 mutant was identified as a nifA type regulatory gene of A. brasilense (a) by genetic complementation with nifA of Klebsiella pneumoniae, (b) by the absence of nitrogenase iron protein in western protein blots and (c) by its inability to activate expression of a nifH-lacZ fusion. The growth characteristics of the three mutants showed that none of them is defective in general nitrogen regulatory (ntr) genes. Also, no homology was detected between the three nif DNA regions of the mutants, cloned in pMS188, pMS189 and pMS197, and the K. pneumoniae nif, glnA or ntr genes. In addition, the fixABC genes of Bradyrhizobium japonicum did not show any hybridization with the cloned Azospirillum genes. Unlike the situation in enteric bacteria, the nif genes in A. brasilense are scattered and span a region of about 65 kb.
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PMID:Identification of a regulatory nifA type gene and physical mapping of cloned new nif regions of Azospirillum brasilense. 255 12

Dinitrogenase from a nifV mutant of Klebsiella pneumoniae contains an altered form of iron-molybdenum cofactor (FeMoco) that lacks a biologically active homocitric acid molecule. Change in the composition of FeMoco led to substantial variation in the kinetics of nitrogenase action. The KmS of the mutant enzyme for N2 and N2O were 0.244 and 0.175 atm (24,714 and 17,726 kPa), respectively. The km for N2 was higher and the Km for N2O was lower than that for the wild-type enzyme. The mutant enzyme was ineffective in N2 fixation, in N2O reduction, and in HD formation, as indicated by the low Vmax of these reactions with saturating levels of substrate and under conditions of saturating electron flux. These observations provide further support for the concept that N2, N2O, and D2 interact with the same form of dinitrogenase. H2 evolution by the mutant enzyme is only partially inhibited by CO. Observation that different numbers of electrons are stored in CO-inhibited than in noninhibited dinitrogenase before H2 is released suggests that the mutant enzyme has more sites responsible for H2 evolution than the wild-type enzyme, whose H2 evolution is not inhibited by CO.
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PMID:N2O reduction and HD formation by nitrogenase from a nifV mutant of Klebsiella pneumoniae. 265 43

A total of 35 coliforms isolated from bovine intramammary infections were tested for serum susceptibility. Growth responses of Klebsiella pneumoniae isolated from intramammary infections originating during the dry period were inhibited more than were growth responses of Klebsiella pneumoniae isolated from infections originating during lactation. Escherichia coli growth responses did not differ between isolates originating from dry period and lactational intramammary infections. Mean growth responses to serum did not differ between Klebsiella pneumoniae and Escherichia coli. Bactericidal properties of serum were due to complement activity. The classical pathway of complement appeared to be the principal source of bactericidal activity of serum toward Klebsiella pneumoniae. Alternative and classical pathways of complement were both important for bactericidal effects of serum on Escherichia coli. Iron saturation of serum did not affect growth responses of either Klebsiella pneumoniae or Escherichia coli. These data illustrate that coliforms isolated from intramammary infection originating during the dry period were not more resistant to the bactericidal activity of bovine serum than were coliforms isolated from intramammary infection occurring during lactation.
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PMID:Serum susceptibility of coliforms isolated from bovine intramammary infections. 267 30

Crude extracts of wild-type, nitrogenase-derepressed Klebsiella pneumoniae fractionated by nondenaturing gel electrophoresis contain, in addition to the major form of the MoFe protein, two minor variants of lower electrophoretic mobility. Of seven Nif- mutants of K. pneumoniae with nonpolar point mutations in nifD (encoding the alpha subunit of Kp1), three exhibit a wild-type-like electrophoretic pattern, whereas in the remaining four, the slowest-migrating form becomes the predominant species. Amino acid substitutions in mutants of the first type are located in the N terminus of NifD and include Gly-85 to Arg (UN1661), Glu-121 to Lys (UN1649), and Gly-161 to Asp (UN1683). Mutations of the second type are Gly-186 to Asp (UN1648), Gly-195 to Glu (UN1680), Ser-443 to Pro (UN1793), and Gly-455 to Asp (UN1650). Six of the mutated residues show interspecies conservation, three are close to conserved cysteines, and two are located next to conserved histidines. Based on evidence pointing to the possibility that the lowest-mobility form lacks the iron-molybdenum cofactor, these results provide insights into the functional significance of specific sites in the alpha subunit of the MoFe protein.
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PMID:Structure-function relationships in the alpha subunit of Klebsiella pneumoniae nitrogenase MoFe protein from analysis of nifD mutants. 267 89

Rhodobacter capsulatus genes homologous to Klebsiella pneumoniae nifE, nifN and nifX were identified by DNA sequence analysis of a 4282 bp fragment of nif region A. Four open reading frames coding for a 51,188 (NifE), a 49,459 (NifN), a 17,459 (NifX) and a 17,472 (ORF4) dalton protein were detected. A typical NifA activated consensus promoter and two imperfect putative NifA binding sites were located in the 377 bp sequence in front of the nifE coding region. Comparison of the deduced amino acid sequences of R. capsulatus NifE and NifN revealed homologies not only to analogous gene products of other organisms but also to the alpha and beta subunits of the nitrogenase iron-molybdenum protein. In addition, the R. capsulatus nifE and nifN proteins shared considerable homology with each other. The map position of nifX downstream of nifEN corresponded in R. capsulatus and K. pneumoniae and the deduced molecular weights of both proteins were nearly identical. Nevertheless, R. capsulatus NifX was more related to the C-terminal end of NifY from K. pneumoniae than to NifX. A small domain of approximately 33 amino acid residues showing the highest degree of homology between NifY and NifX was also present in all nifB proteins analyzed so far. This homology indicated an evolutionary relationship of nifX, nifY and nifB and also suggested that NifX and NifY might play a role in maturation and/or stability of the iron-molybdenum cofactor. The open reading frame (ORF4) downstream of nifX in R. capsulatus is also present in Azotobacter vinelandii but not in K. pneumoniae.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:DNA sequence and genetic analysis of the Rhodobacter capsulatus nifENX gene region: homology between NifX and NifB suggests involvement of NifX in processing of the iron-molybdenum cofactor. 274 20


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