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Biomedical subjects

E L Schmidt

Publications and source records attributed to E L Schmidt.

At least 19 recordsLinked to original sources
PubMed1999

[A method of quality assurance of dynamic wedges].

BACKGROUND: One of the important prerequisites for using a virtual wedge is the availability of an appropriate method for quality assurance. A simple method to determine wedge angles has been developed. MATERIAL AND METHODS: A formula based on the exponential attenuation curve has been derived, that allows for the calculation of the wedge isodose angles based on 2 measurement points perpendicular to the central ray. The linear attenuation coefficient is the only variable that must be known for the field size under consideration. RESULTS: Using the algorithm introduced, the wedge angle isodoses can be measured with a high degree of accuracy. The deviation of the wedge angle compared to the measurements done according to DIN 6847-4 is less than 1 degree. CONCLUSION: The described procedure is a simple method of performing routine quality assurance for the virtual wedge.

Algorithms↗
PubMed1996

Development of methods for dynamic radiation therapy with specified dose distributions.

Several methods for dose deposition of a given isodose distribution were developed by implementation of different techniques of accelerator use. Common to all of these methods is the time-dependent change of certain accelerator parameters during radiation treatment. The accelerators for which these methods can be used are equipped with independent collimator jaws, however, not with any kind of multileaf collimation. This method was designed to deposit a certain group of dose distributions that are restricted by a small number of constraints. The developed methods were implemented into a digitally controlled medical linear accelerator and the dosimetric results of such treatments were evaluated. Dose distributions with spatial dependencies in one and in two dimensions were deposited by movement of one X-ray jaw pair. Furthermore, a method for generation of a two-dimensional rotationally symmetric dose distribution was developed.

Algorithms↗
PubMed1996

Development of a fast optimization preview in radiation treatment planning.

PURPOSE: Having the capability of fast previewing an expected optimization result for a defined combination of optimization parameters is essential to reach a better optimization result. In order to achieve this goal, the well-tried Cimmino optimization algorithm requires modification. MATERIALS AND METHODS: Usually, the speed of convergence of some iterative algorithms is restricted to a bounded relaxation parameter. Exploiting the special altering behavior of the weighting factors at each step, many iteration steps are avoided by overrelaxing this relaxation parameter. Therefore, the relaxation parameter is increased as long as the optimization result is improved. This can be performed without loss of accuracy. RESULTS: Our optimization technique is demonstrated by the case of a right lung carcinoma. The solution space for this case is 36 isocentric X-ray beams evenly spaced at 10 degree. Each beam is restricted to 23 MV X-ray fields with a planning target volume matched by irregular field shapes, similar to that produced by a multileaf collimator. Four organs at risk plus the planning target volume are considered in the optimization process. The convergence behavior of the optimization algorithm is shown by overrelaxing the relaxation parameter in comparison to conventional relaxation parameter control. CONCLUSION: The new approach offers the ability to get a fast preview of the expected final result. If the clinician is in agreement with the preview, the algorithm is continued and achieves the result proven by the Cimmino optimization algorithm. In the other case, if the clinician doesn't agree with the preview, he will be able to change the optimization parameters (e.g., field entry points) and to restart the algorithm.

Algorithms↗
PubMed1993

Plasmids pJP4 and r68.45 Can Be Transferred between Populations of Bradyrhizobia in Nonsterile Soil.

IncP plasmid r68.45, which carries several antibiotic resistance genes, and IncP plasmid pJP4, which contains genes for mercury resistance and 2,4-dichlorophenoxyacetic acid degradation, were evaluated for their ability to transfer to soil populations of rhizobia. Transfer of r68.45 was detected in nonsterile soil by using Bradyrhizobium japonicum USDA 123 as the plasmid donor and several Bradyrhizobium sp. strains as recipients. Plasmid transfer frequencies ranged up to 9.1 x 10 in soil amended with 0.1% soybean meal and were highest after 7 days with strain 3G4b4-RS as the recipient. Transconjugants were detected in 7 of 500 soybean nodules tested, but the absence of both parental strains in these nodules suggests that plasmid transfer had occurred in the soil, in the rhizosphere, or on the root surface. Transfer of degradative plasmid pJP4 was also evaluated in nonsterile soil by using B. japonicum USDA 438 as the plasmid donor and several Bradyrhizobium sp. strains as recipients. Plasmid pJP4 was transferred only when strains USDA 110-ARS and 3G4b4-RS were the recipients. The plasmid transfer frequency was highest for strain 3G4b4-RS (up to 7.4 x 10). Mercury additions to soil, ranging from 10 to 50 mug/g of soil, did not affect population levels of parental strains or the plasmid transfer frequency.

Journal Article↗
PubMed1992

Lysogeny in Bradyrhizobium japonicum and Its Effect on Soybean Nodulation.

Rhizobiophage V, isolated from soil in the vicinity of soybean roots, was strongly lytic on Bradyrhizobium japonicum 123B (USDA 123) but only mildly lytic on strain L4-4, a chemically induced small-colony mutant of 123. Numerous bacteriophage-resistant variants were isolated from L4-4 infected with phage V; two were studied in detail and shown to be lysogenic. The two, L4-4 (V5) and L4-4 (V12), are the first reported examples of temperate-phage infection in B. japonicum. Phage V and its derivative phages V5 and V12 were closely related on the basis of common sensitivity to 0.01 M sodium citrate and phage V antiserum, phage immunity tests, and apparently identical morphology when examined by electron microscopy. However, the three phages differed in host range and in virulence. Lysogens L4-4 (V5) and L4-4 (V12) were immune to infection by phages V and V5 but not to infection by V12. Southern hybridization analysis confirmed the incorporation of phage V into the genomes of strains L4-4(V5) and L4-4(V12) and also demonstrated the incorporation of phage V into the genome of a phage V-resistant derivative of USDA 123 designated 123 (V2). None of the three lysogens, L4-4(V5), L4-4(V12), or 123B(V2), was able to nodulate soybean plants. However, Southern hybridization profile data indicated that phage V had not incorporated into any of the known B. japonicum nodulation genes.

Journal Article↗
PubMed1991

Transfer of the Pea Symbiotic Plasmid pJB5JI in Nonsterile Soil.

Transfer of the pea (Pisum sativum L.) symbiotic plasmid pJB5JI between strains of rhizobia was examined in sterile and nonsterile silt loam soil. Sinorhizobium fredii USDA 201 and HH003 were used as plasmid donors, and symbiotic plasmid-cured Rhizobium leguminosarum 6015 was used as the recipient. The plasmid was carried but not expressed in S. fredii strains, whereas transfer of the plasmid to R. leguminosarum 6015 rendered the recipient capable of nodulating pea plants. Confirmation of plasmid transfer was obtained by acquisition of plasmid-encoded antibiotic resistance genes, nodulation of pea plants, and plasmid profiles. Plasmid transfer in nonsterile soil occurred at frequencies of up to 10 per recipient and appeared to be highest at soil temperatures and soil moisture levels optimal for rhizobial growth. Conjugation frequencies were usually higher in sterile soil than in nonsterile soil. In nonsterile soil, transconjugants were recovered only with strain USDA 201 as the plasmid donor. Increasing the inoculum levels of donor and recipient strains up to 10 cells g of soil increased the number of transconjugants; peak plasmid transfer frequencies, however, were found at the lower inoculum level of 10 cells g of soil. Plasmid transfer frequencies were raised in the presence of the pea rhizosphere or by additions of plant material. Transconjugants formed by the USDA 201(pJB5JI) x 6015 mating in soil formed effective nodules on peas.

Journal Article↗
PubMed1989

Nodulating Competitiveness of a Nonmotile Tn7 Mutant of Bradyrhizobium japonicum in Nonsterile Soil.

A nonmotile mutant of Bradyrhizobium japonicum serogroup 127 was generated by Tn7 mutagenesis and matched with the wild type against a common competitor in studies of soybean nodulation in nonsterile soil. The Tn7 mutant was very similar to the wild type in growth rate in culture, soybean lectin-binding ability, flagellar morphology, and nodulating capability, but it had a longer lag phase. Competing strains were distributed uniformly in soil in various ratios and at different population densities prior to planting. Mutant and wild type were equally prevalent in the seedling rhizosphere at about the time of nodule initiation, suggesting that motility conferred no advantage in rhizosphere colonization. Nodulation success of the Tn7 mutant was lower than that of the wild type under all test conditions. Differences were greatest at low soil populations of competitors and much less pronounced at initial populations of 10 g. The longer lag phase of the Tn7 mutant may have contributed to its decreased competitiveness, especially at the higher inoculation levels. The antibiotic and motility markers were stable, and the rifampin resistance derived from the parent did not affect adversely the competitiveness of the Tn7 mutant. We found motility to be of limited importance to the competitiveness of a strain in normal nonsterile soil, where the significance, if any, of this ability may be in migration at the immediate root surface in soils sparsely populated with rhizobial symbionts.

Journal Article↗
PubMed1988

An acidophilic and a neutrophilic nitrobacter strain isolated from the numerically predominant nitrite-oxidizing population of an Acid forest soil.

Two physiologically and serologically distinct strains of chemoautotrophic nitrite-oxidizing bacteria were isolated as numerically predominant members of the nitrite-oxidizer population of an undisturbed forest soil with a pH range of 4.3 to 5.2. One isolate responded as a neutrophile, characteristic of the family Nitrobacteraceae, and cross-reacted strongly with fluorescent antibody to Nitrobacter strain Engel. The second isolate responded as an acidophile in pure culture, demonstrated maximal nitrite oxidation activity at pH 5.5, and had a pH tolerance range of pH 4.1 to 7.2. Nitrite oxidase in whole cells of the acidophile sustained activity to at least pH 3.5. Cell morphology of both strains typified the genus Nitrobacter in all respects when cultured at pH 7. However, under more acidic conditions the acidophile tended to elongate and at times appeared to branch. These data provide the first evidence for the existence of an acidophilic chemoautotrophic nitrifying bacterium. Isolation of the neutrophilic Nitrobacter strain reported here complements the earlier isolation of a neutrophilic Nitrosospira strain to provide further evidence of a prominent acid-intolerant population of chemoautotrophic nitrifiers in this acid forest soil.

Journal Article↗
PubMed1987

Ecology of Indigenous Soil Rhizobia: Response of Bradyrhizobium japonicum to Readily Available Substrates.

Populations of indigenous Bradyrhizobium japonicum serocluster 123 and serogroups 110 and 138 were studied after various sugars were added to their soil habitat. Loam soil with approximately 10 cells of each group per g of soil were amended every 3 days with 0.1% glucose, sucrose, arabinose, xylose, or galactose. Enumerations of the populations were made every 12 days by immunofluorescence assay. Each B. japonicum population in the sugar-treated soils increased by about 1 log during the first 12 days, to a maximum of about 10 cells by day 36 or 48, irrespective of the sugar added. Maximum growth rates were similar for each group and occurred during the 12-day incubation period. The most rapid growth was in response to arabinose, with a mean generation time of about 3.0 days. Other mean doubling times were 4.0 days with glucose and galactose treatments, 4.5 days with xylose treatment, and 5.4 days with sucrose amendment. These data provide the first direct evidence that indigenous soil rhizobia can compete successfully with other soil bacteria for readily available substrates in soil in the absence of host legume roots or other rhizospheres. The growth rates in soil of the specific B. japonicum populations studied were nearly the same with a given sugar treatment but varied considerably with different sugars. The mean generation times of 3 to 5 days are among the first reported growth rates for heterotrophic bacteria in natural soil.

Journal Article↗
PubMed1986

Bradyrhizobium japonicum Serocluster 123 and Diversity among Member Isolates.

Diversity was examined within a group of 79 isolates of Bradyrhizobium japonicum reactive to fluorescent antibodies (FAs) prepared against B. japonicum USDA 123. Analyses were by means of cross-adsorbed FAs, bacteriophage typing, and endonuclease restriction digest patterns. Serogroups 127 and 129 shared antigenic determinants with serogroup 123 but not with each other. Bacteriophage and DNA digest patterns reflected more common features between serogroups 123 and 127 than between 123 and 129. Serogroups 129 and 122 showed FA cross-reactivity. The term serocluster was proposed to reflect interrelationships observed among the serogroups.

Journal Article↗
PubMed1984

Rhizosphere Response as a Factor in Competition Among Three Serogroups of Indigenous Rhizobium japonicum for Nodulation of Field-Grown Soybeans.

Rhizosphere response was studied as a factor in competition among indigenous Rhizobium japonicum serogroups for the nodulation of soybeans under field conditions. R. japonicum serogroups 110, 123, and 138 were found to coexist in a Waukegan field soil where they were determined to be the major nodulating rhizobia in soybean nodules. Competitive relationships among the three serogroups in that soil and in rhizospheres were examined during two growing seasons with several host cultivars with and without inoculation and with a nonlegume. Enumeration of each of the three competitors was carried out on inner rhizosphere and nonrhizosphere soil by immunofluorescence with serogroup-specific fluorescent antibodies. Rhizobia present in early- and late-season nodules were identified by fluorescent antibody analysis. Populations of each serogroup increased gradually in host rhizospheres, not exceeding 10/g of rhizosphere soil during the first few weeks after planting, whereas numbers in fallow soil remained at initial levels (10 to 10/g). The rhizosphere effects were minor in host plants during this period of nodule initiation and were about the same for all three serogroups. Although serogroup 123 gave no evidence of dominance in early host rhizospheres, it clearly dominated in nodule composition, occupying 60 to 100% of the nodules. High densities of all three serogroups were observed in host rhizospheres during flowering. Rhizosphere populations, especially of serogroup 123, were still high during pod fill and seed maturation. The rhizosphere responses of the R. japonicum serogroups were much greater with the soybean cultivars than with oats, but even in host rhizospheres the R. japonicum populations were greatly outnumbered by other bacteria. The success of serogroup 123 in achieving nodulation does not appear to be due to superior colonization of the host rhizosphere.

Journal Article↗
PubMed1983

Population Changes and Persistence of Rhizobium phaseoli in Soil and Rhizospheres.

The impact of legume cultivation on the establishment and persistence of an inoculant strain of Rhizobium phaseoli and its ability to compete with a resident population of R. phaseoli for nodule occupancy was examined utilizing strain-specific fluorescent antibodies. The soil (Hubbard loamy sand) was inoculated homogeneously with 5 x 10 cells per g of soil and confined in plastic cylinders kept in field plots. Inoculated and uninoculated cylinders were either left fallow or planted to two seeds of legumes. Two hosts, navy bean (Phaseolus vulgaris L.) cv. Seafarer and snap bean cv. Picker, as well as a nonhost, soybean (Glycine max (L.) Merr.) cv. Wilkin, were used. Inoculant Viking 1 was highly stimulated in all three rhizospheres sampled at 6 (flowering), 10 (podfill), and 17 (decay) weeks and in the following spring, whereas counts in fallow soil decreased rapidly. Although the overwintering population remained highest in the vicinity of decaying host roots, Viking 1 persisted, even in fallow soil, to produce abundant nodulation of host plants the following spring. Viking 1 was an excellent competitor for nodulation sites on the roots of the hosts; it thoroughly outcompeted the resident population of R. phaseoli, occupying virtually 100% of the nodules under inoculated conditions in all experiments.

Journal Article↗
PubMed1983

Initial stages in the morphogenesis of nitrogen-fixing stem nodules of Sesbania rostrata.

Morphogenesis of stem nodules in Sesbania rostrata was studied over a period of 6 days after inoculation with an appropriate species of Rhizobium. Nodulation sites were initially slightly raised, circular areas 0.3 to 0.6 mm in diameter and 4 to 5 mm apart in vertical rows along the length of the stem. Each site was underlaid by an adventitious root primordium. A site became susceptible to infection by a specific Rhizobium sp. when the root primordium broke through the epidermis, leaving a fissure. Rhizobia multiplied within this fissure and colonized the exposed intercellular spaces. The infection extended inward as narrow, branched intercellular threads moved into a cortical meristematic zone, where cell division was initiated, and invagination of infection thread branches into adjacent plant cells followed. Rhizobia were released into the plant cells and surrounded immediately by plant membrane. Intracellular rhizobia divided actively, leading to bacteroid-filled cells. Infected areas enlarged and coalesced as the nodule matured.

Cells, Cultured↗
PubMed1981

The isolation and characterization of a root lectin from soybean (Glycine max (L), cultivar Chippewa).

A lectin has been isolated from the roots of 5-day soybean (Glycine max (L) cultivar Chippewa) seedlings, and its properties have been compared to those of the soybean seed lectin. The sugar-binding activities of the two lectins, both in terms of specific hemagglutinating activity and sugar specificity, are indistinguishable. Molecular properties of the two lectins, measured as relative molecular weights, isoelectric and electrophoretic patterns, amino acid compositions, immunochemical cross-reactivity, and chromatographic behavior on Sepharose-concanavalin A adsorbents suggest that the seed and the root lectin are very similar but not identical. On the basis of these comparisons, we conclude that models regarding biological functions of soybean lectin derived from studies using the seed lectin can be extended to include the root lectin in this cultivar. Studies on the distribution of the lectin in the root tissue suggest that it is associated with the outer surface of the root and is concentrated in the segments of the root at which hair and early secondary roots are observed. Since this is the region at which Rhizobium binding occurs and at which nodulation probably is initiated, all the reported observations on the root lectin are consistent with its proposed role in the specific interaction of the developing soybean with its symbiont.

Acetylgalactosamine↗
PubMed1981

Inhibitory effect of nitrapyrin on three genera of ammonia-oxidizing nitrifiers.

Five strains of Nitrosomonas and one each of Nitrosospira and Nitrosolobus were examined for sensitivity to the nitrification inhibitor nitrapyrin. Considerable variation in sensitivity was observed, with some strains about five times more resistant than others. Sensitivity to nitrapyrin varied more with strain than with genus.

Journal Article↗