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.     

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 properties of enhancer-bypass mutants of sigma 54

The N-terminal activation domain of Escherichia coli sigma 54 was randomly mutated to provide a library of changes that might allow the required enhancer function to be bypassed. Five clones harbouring mutant sigma factors were obtained that exhibited this property in that they enhanced growth under nitrogen-limiting conditions in cells lacking NtrC. DNA sequence analysis located all mutations to four leucines in a small region between amino acids 25 and 31. No mutant sigma factors retained the hydrophobic character of the leucine residues. Mutant sigma factors were shown to transcribe in vitro without the need for enhancer binding activator or ATP hydrolysis, confirming the in vivo phenotype. These and other data suggest that a very small set of leucines is critical for keeping polymerase function in check, allowing high responsiveness to physiological induction via enhancer proteins such as NtrC.     

Selection of auxotrophic and carbohydrate-negative mutants in penicillin-resistant Klebsiella pneumoniae by nalidixic acid treatment

Abstract The bactericidal antibiotic nalidixic acid can be used to select in cultures of Klebsiella pneumoniae and other penicillin-resistant enteric bacteria any auxotrophic and carbohydrate-negative mutant. Nalidixic acid treatment is superior to penicillin or d -cycloserine treatment, since no cross-feeding by lysed cells is possible, and it is simple to handle.     

Single amino acid substitutions in puroindoline-b mutants influence lipid binding properties

External reflectance Fourier transform infrared (ER-FTIR) spectroscopy and surface pressure measurements have been used to characterize the interaction of wild-type puroindoline-b (Pin-b) and two mutant forms featuring single residue substitutions-namely, Gly-46 to Ser-46 (Pin-bH) and Trp-44 to Arg-44 (Pin-bS)-with condensed-phase monolayers of zwitterionic (L-alpha-dipalmitoylphosphatidylcholine, DPPC) and anionic (L-alpha-dipalmitoylphosphatidyl-dl-glycerol, DPPG) phospholipids. The interaction with anionic DPPG monolayers, monitored by surface pressure isotherms, was influenced significantly by mutations in Pin-b (p < 0.05); wild-type Pin-b showed the highest surface pressure change of 10.6 +/- 1.0 mN m-1, followed by Pin-bH (7.9 +/- 1.6 mN m-1) and Pin-bS (6.3 +/- 1.0 mN m-1), and the surface pressure isotherm kinetics were also different in each case. Integrated Amide I peak areas from corresponding ER-FTIR spectra confirmed the differences in adsorption kinetics, but also showed that differences in adsorbed amount were less significant, suggesting that mutations influence the degree of penetration into DPPG films. All Pin-b types showed evidence of interaction with DPPC films, detected as changes in surface pressure (5.6 +/- 1.1 mN m-1); however, no protein peaks were detected in the ER-FTIR spectra, which indicated that the interaction was via penetration with limited adsorption at the lipid/water interface. The expression of Pin-b mutants is linked to wheat endosperm hardness; therefore, the data presented here suggest that the lipid binding properties may be pivotal within the mechanism for this quality trait. In addition, the data suggest antimicrobial activities of Pin-b mutants would be lower than those of the wild-type Pin-b, because of decreased selectivity toward anionic phospholipids.     

An amino acid substitution determining G3m(g)

An allotypic G3m(g) marker-specific substitution was studied by sequence analysis of glycopeptides derived from myeloma proteins Ba (G3m(g+)) and Bu (G3m(g-)). The experimental results indicate that glutamic acid at position 295 is responsible for the specificity. Based on the results of chemical modification (Arg, Tyr, and Glu), this antigenic epitope is presumed to involve five sequential residues from Arg-292 to Tyr-296.     

Isolation and characterization of prototrophic relaxed mutants of Klebsiella pneumoniae

Summary A new selection procedure has been developed for isolating prototrophic relaxed mutants of Klebsiella pneumoniae. Two mutants were isolated. One of them showed a fully relaxed phenotype, while the other one behaved in a semi-relaxed way.The wild-type strain, as well as the rel mutants exerted similar patterns to their E. coli counterparts in RNA, protein, ppGpp and pppGpp accumulation during amino starvation, carbon source shift-down and nitrogen starvation. Both mutants became stringent after introducing an F-factor carrying the relA ⁺ allele from Escherichia coli. The relaxed phenotype could be recovered by curing the F-factor. Some of the pleiotropic consequences of rel mutations found in E. coli are present in the Klebsiella mutants also while some of them are absent.The mutants are defective in dinitrogen fixation after the exhaustion of limiting ammonium from the culture medium. However, their merodiploid derivatives, carrying the E. coli relA ^- allele, showed the wild-type level of nitrogenase activity under the same conditions.Fellow of the 6th International Training Course jointly sponsored by UNDP/UNESCO Hungarian Academy of Sciences. Present address: Akademie der Wissenschaften der DDR, Forschungszentrum für Molekularbiologie und Medizin, Zentralinstitut für Mikrobiologie und Experimentelle Therapie Jena, Beuthenberg Str. 11, DDR-69 Jena