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E G Niemann

Publications and source records attributed to E G Niemann.

11 recordsLinked to original sources
PubMed1990

Nitrogen Fixation in Continuous Culture with NH(4)Cl-Containing Media.

N balance and N dilution were determined from growth of Azospirillum brasilense Sp7 and two unidentified gram-negative nitrogen-fixing microorganisms in continuous culture supplied with NH(4)Cl. At the 1.1 and 2.2 mM NH(4)Cl steady states (N-to-C ratios of 1:68 and 1:34, respectively), the organisms grew with NH(4)Cl and N(2) as N sources simultaneously under carbon limitation. No ammonium could be detected in the supernatant of these cultures.

Journal Article↗
PubMed1987

Root-Zone-Specific Oxygen Tolerance of Azospirillum spp. and Diazotrophic Rods Closely Associated with Kallar Grass.

The effect of oxygen on N(2)-dependent growth of two Azospirillum strains and two diazotrophic rods closely associated with roots of Kallar grass (Leptochloa fusca) was studied. To enable precise comparison, bacteria were grown in dissolved-oxygen-controlled batch and continuous cultures. Steady states were obtained from about 1 to 30 muM O(2), some of them being carbon limited. All strains needed a minimum amount of oxygen for N(2)-dependent growth. Nitrogen contents between 10 and 13% of cell dry weight were observed. The response of steady-state cultures to increasing O(2) concentrations suggested that carbon limitation shifted to internal nitrogen limitation when N(2) fixation became so low that the bacteria could no longer meet their requirements for fixed nitrogen. For Azospirillum lipoferum Rp5, increase of the dilution rate resulted in decreased N(2) fixation in steady-state cultures with internal nitrogen limitation. Oxygen tolerance was found to be strain specific in A. lipoferum with strain Sp59b as a reference organism. Oxygen tolerance of strains from Kallar grass was found to be root zone specific. A. halopraeferens Au 4 and A. lipoferum Rp5, predominating on the rhizoplane of Kallar grass, and strains H6a2 and BH72, predominating in the endorhizosphere, differed in their oxygen tolerance profiles. Strains H6a2 and BH72 still grew and fixed nitrogen in steady-state cultures at O(2) concentrations exceeding those which absolutely inhibited nitrogen fixation of both Azospirillum strains. It is proposed that root-zone-specific oxygen tolerance reflects an adaptation of the isolates to the microenvironments provided by the host plant.

Journal Article↗
PubMed1986

Close association of azospirillum and diazotrophic rods with different root zones of kallar grass.

The populations of diazotrophic and nondiazotrophic bacteria were estimated in the endorhizosphere and on the rhizoplane of Kallar grass (Leptochloa fusca) and in nonrhizosphere soil. Microaerophilic diazotrophs were counted by the most-probable-number method, using two semisolid malate media, one of them adapted to the saline-sodic Kallar grass soil. Plate counts of aerobic heterotrophic bacteria were done on nutrient agar. The dominating N(2)-fixing bacteria were differentiated by morphological, serological, and physiological criteria. Isolates, which could not be assigned to a known species, were shown to fix nitrogen unequivocally by N(2) incorporation. On the rhizoplane we found 2.0 x 10 diazotrophs per g (dry weight) of root, which consisted in equal numbers of Azospirillum lipoferum and Azospirillum-like bacteria showing characteristics different from those of known Azospirillum species. Surface sterilization by NaOCI treatment effectively reduced the rhizoplane population, so that bacteria released by homogenization of roots could be regarded as endorhizosphere bacteria. Azospirillum spp. were not detected in the endorhizosphere, but diazotrophic, motile, straight rods producing a yellow pigment occurred with 7.3 x 10 cells per g (dry weight) of root in the root interior. In nonrhizosphere soil we found 3.1 x 10 nitrogen-fixing bacteria per g. Diazotrophs were preferentially enriched in the Kallar grass rhizosphere. In nonrhizosphere soil they made up 0.2% of the total aerobic heterotrophic microflora, on the rhizoplane they made up 7.1%, and in the endorhizosphere they made up 85%. Owing to high numbers in and on roots and their preferential enrichment, we concluded that diazotrophs are in close association with Kallar grass. They formed entirely different populations on the rhizoplane and in the endorhizosphere.

Journal Article↗
PubMed1983

Investigations on the mechanism of photodynamic action of different psoralens with DNA.

Investigations on the photodynamic action of psoralens with DNA were performed, using experimental techniques of fluorescence lifetime and NMR-CIDNP, as well as SCF-MO and CNDO molecular orbital calculations. It has been shown that the formation of a biradical through the triplet state is the decisive step for psoralen dimer formation, as well as for cyclobutane addition with thymine, while singlet oxygen production is responsible for enzyme inactivation (e.g., lysozyme and trypsin). The molecular orbital calculations, in agreement with experimental results, indicate that the differences in biological effectivity of different psoralens are based on variations in triplet formation probability.

Animals↗
PubMed1983

Electric field effects on bacteria and yeast cells.

Comparative studies were carried out describing the lethal effects of electric pulses on GRAM-negative bacteria, GRAM-positive bacteria, and yeast cells. Microorganisms are killed by the pulse treatment without visible morphological destruction. The observed survival rates are figured as functions of the field strength E and the treatment time t (pulse number X time constant) revealing three explicit parameters as sufficient to explain the kinetics of the results. These parameters are determined by the species of microorganism used and moreover depend on the physiological properties of the microbial population. GRAM-positive bacteria and yeasts were found to be less sensitive to electric pulse treatment than GRAM-negative bacteria, when low pulse numbers are applied. Treatment with high pulse numbers reveals survival rates below 1% for all microorganisms examined. Cells from the logarithmic growth phase are killed in markedly higher percentage than cells harvested from the stationary growth phase. The obtained results as well as further studies confirm the hypothesis of an electric induced selective damage of inner cell membranes.

Bacteria↗
PubMed1981

Killing of bacteria with electric pulses of high field strength.

Bacteria of the type E. coli K12 have been treated in experiments using high-voltage pulses of short time (microseconds) as a killing agent. The role of different experimental parameters has been studied: kind of electrolyte, concentration, length of pulses, field strength, pH and temperature. Electrolytes with bivalent cations were found to reduce the lethal action. the relative rate of killed bacteria was shown to be mainly governed by the field strength and the treatment time, which is defined by the product of pulse number and decay time constant. From the obtained results a function has been developed which enables the precalculation of the killing rate for E. coli, provided that certain limits of experimental conditions are considered. No correlation between the applied electric energy and the lethal effect could be found.

Bacterial Physiological Phenomena↗
PubMed1980

Lethal effects of high-voltage pulses on E. coli K12.

The lethal effects of high-voltage capacitor-discharges in suspensions of E. coli K12 with varying electrolytes have been examined. A reduction of more than 99.9% of living cells, dependent on the applied voltage could be proved. The bactericidal action is assumed to be due to direct effects of high electric fields. Electrolytically produced chlorine was shown to act as an additional toxic agent, when chloride is present in the treated medium. The relative survival rate of bacteria has been found to depend also on the concentration of cells during pulse treatment.

Cell Membrane↗