Viability of Rhizobium bacteroids.

Bacteroids prepared from nodules of soybean and bean were tested for viability. Contrary to the prevailing view that bacteroids are nonviable, it was found that bacteroids averaged 90% viability, irrespective of Rhizobium strain, nodule age, or nodule environment.     

Viability of Rhizobium bacteroids.

Bacteroids prepared from nodules of soybean and bean were tested for viability. Contrary to the prevailing view that bacteroids are nonviable, it was found that bacteroids averaged 90% viability, irrespective of Rhizobium strain, nodule age, or nodule environment.     

Fatty acid composition of Rhizobium spp.

The fatty acid composition of 42 isolates belonging to the major plant affinity groups of Rhizobium has been determined and found to vary reproducible with culture age. Numerical taxonomic techniques applied to the 15 major fatty acid components of log-phase cultures of comparable physiological age showed that the rhizobia constitute a uniform group. However, two clusters comprising soybean-cowpea isolates and pea-bean isolates were evident. These observations, based on a simple analysis of only one group of chemical components, indicate relationships among rhizobia which differ from the conventional plant-affinity groupings but which are consistent with other proposed relationships established using a variety of biochemical and physiological criteria.     

Reiterated DNA sequences in Rhizobium and Agrobacterium spp.

Repeated DNA sequences are a general characteristic of eucaryotic genomes. Although several examples of DNA reiteration have been found in procaryotic organisms, only in the case of the archaebacteria Halobacterium halobium and Halobacterium volcanii [C. Sapienza and W. F. Doolittle, Nature (London) 295:384-389, 1982], has DNA reiteration been reported as a common genomic feature. The genomes of two Rhizobium phaseoli strains, one Rhizobium meliloti strain, and one Agrobacterium tumefaciens strain were analyzed for the presence of repetitive DNA. Rhizobium and Agrobacterium spp. are closely related soil bacteria that interact with plants and that belong to the taxonomical family Rhizobiaceae. Rhizobium species establish a nitrogen-fixing symbiosis in the roots of legumes, whereas Agrobacterium species is a pathogen in different plants. The four strains revealed a large number of repeated DNA sequences. The family size was usually small, from 2 to 5 elements, but some presented more than 10 elements. Rhizobium and Agrobacterium spp. contain large plasmids in addition to the chromosomes. Analysis of the two Rhizobium strains indicated that DNA reiteration is not confined to the chromosome or to some plasmids but is a property of the whole genome.     

Effect of Compressed Carbon Dioxide on Microbial Cell Viability

In order to study the influence of compressed carbon dioxide, over a range of pressures (1.5 to 5.5 MPa) and exposure times (up to 7 h), on the survival of Escherichia coli, Saccharomyces cerevisiae, and Enterococcus faecalis, a new pressurizable reactor system was conceived. Microbial cells were inoculated onto a solid hydrophilic medium and treated at room temperature; their sensitivities to inactivation varied greatly. The CO₂ treatment had an enhanced efficiency in cell destruction when the pressure and the duration of exposure were increased. The effects of these parameters on the loss of viability was also studied by response-surface methodology. This study showed that a linear correlation exists between microbial inactivation and CO₂ pressure and exposure time, and in it models were proposed which were adequate to predict the experimental values. The end point acidity was measured for all the samples in order to understand the mechanism of microbial inactivation. The pHs of the treated samples did not vary, regardless of the experimental conditions. Other parameters, such as water content and pressure release time, were also investigated.     

抑制浓度下锰铁对啤酒废酵母产LYCD活力影响

目的:探讨锰铁离子对啤酒废酵母产生活性酵母细胞衍生物(LYCD)的活力影响.方法:以啤涌废酵母为研究对象、以废液为培养基,在生长抑制浓度下,分别研究了锰、铁离子的作用浓度与时间对啤酒废酵母产生LYCD的活力影响.结果:废酵母在废液中培养28h可达到对数生长期;当废液中Mn~(2+)、Fe~(3+)浓度分别达到200mg/L、50mg/L时可对废酵母产生生长抑制;当Mn~(2+)、Fe~(3+)的作用浓度分别为220mg/L、60mg/L、应激时间分别是25、45min时,啤酒废酵母产的LYCD活性强.结论:应激培养基中金属离子Mn~(2+)、Fe~(3+)达到一定浓度,在一定时间下可使废酵母产生强活力的LYCD.     

Effect of Terminal Aneuploidy on Epidermal Cell Viability in DROSOPHILA MELANOGASTER

In Drosophila melanogaster, individuals heterozygous for translocations between chromosomes Y and 3 can generate, by means of mitotic recombination, somatic cells bearing duplications and deletions. Using translocations with different breakpoints, I have studied the behavior of clones of cells with increasing degrees of aneuploidy in the abdominal cuticle. Both hyper- and hypoploid cells can survive being duplicated or deficient even for large chromosome 3 fragments. While hyperploidy does not severely affect cell viability, the recovery of hypoploid clones decreases linearly as a function of the size of the deleted fragment. In this report, the quantitative and qualitative aspects of this effect are discussed.     

Response of Rhizobium spp. and pea seedlings to glycine

Summary Inhibition of growth of Rhizobium spp. by glycine and by the D-form of an unnatural amino acid, norvaline, was established. Rhizobium trifolii, strain Coryn, was completely inhibited at a glycine concentration of 10 g/ml while in the case of Rhizobium leguminosarum, strain S 310a, at the same glycine concentration only bacteroid-like forms were found.The amino-acid composition of pea and maize seedlings was altered by introducing amino acids into the cotyledons. It was found that the amino compounds were transported to the roots. In the case of peas, glycine was completely converted to serine while in maize this was not the case. L-serine, sarcosine and D-norvaline were found unchanged during the experimental period. re]19750515     

Characterization of Rhizobium etli and other Rhizobium spp. that nodulate Phaseolus vulgaris L. in an Austrian soil

Phaseolus vulgaris L. (common bean) is nodulated by rhizobia present in the fields around the Seibersdorf laboratory despite the fact that common bean has not been grown for a long time. Using PCR analysis with repetitive primers, plasmid profiles, nifH profiles, PCR-RFLP analysis of the 16S rRNA gene and of the 16S rRNA-23S rRNA intergenic spacer and the nodulation phenotype, two well-differentiating groups could be distinguished. One group showed high similarity to Rhizobium sp. R602sp, isolated from common bean in France, while the other showed the same characteristics as R. etli . We detected little variation in the symbiotic regions but found higher diversity when using approaches targeting the whole genome. Many isolates obtained in this study might have diverged from a limited number of strains, therefore the Austrian isolates showed high saprophytic and nodulation competence in that particular soil.     

Chemotaxis of Rhizobium spp. to Plant Root Exudates

Rhizobium spp. show chemotaxis to plant root exudates. Both legumes and non-legume root exudates attract the different rhizobia studied. However, the bacteria show a differential response in that they are attracted to the root exudates of some plants and show no attraction toward others. An example of negative chemotaxis was also observed. The trefoil strain of Rhizobium shows chemotaxis which is qualitatively different from that observed in other bacteria in that simple sugars, di-and trisaccharides, dextrans, and amino acids do not attract this bacterium.     

Effect of Dissolved Oxygen, Temperature, Initial Cell Count, and Sugar Concentration on the Viability of Saccharomyces cerevisiae in Rapid Fermentations

By using 7 x 10(8) cells of Saccharomyces cerevisiae per ml with which 25 degrees Brix honey solutions were fermented to 9.5% (wt/vol; 12% vol/vol) ethanol in 2.5 to 3 h at 30 C, i.e., rapid fermentation, the death rate was found to be high, with only 2.1% of the yeast cells surviving at the end of 3 h under anaerobic conditions. As the dissolved oxygen in the medium was increased from 0 to 13 to 20 to 100% in rapid fermentations at 30 C, there was a progressive increase in the percentage of cells surviving. The ethanol production rate and total were not seriously affected by a dissolved oxygen concentration of 13%, but fermentation was retarded by 20% dissolved oxygen and still further decreased as the dissolved oxygen content reached 100%. When the fermentation temperature was decreased to 15 C (at 13% dissolved oxygen), the rate of fermentation decreased, and the fermentation time to 9.5% ethanol (wt/vol) increased to 6 h. It was found that the higher the temperature between 15 and 30 C, the greater the rate of death as initial cell counts were increased from 1.1 x 10(7) to 7.8 x 10(8) cells per ml. At the lowest level of inoculum, 1.1 x 10(7) cells per ml, there was actual multiplication, even at 30 C; however, the fermentation was no longer rapid. The addition of 15% sugar, initially followed after an hour by the remaining 10%, or addition of the sugar in increments of 2.5 or 5% yielded a better survival rate of yeast cells than when the fermentation was initiated with 25% sugar.     

Influence of Glycine spp. on Competitiveness of Bradyrhizobium japonicum and Rhizobium fredii

The displacement of indigenous Bradyrhizobium japonicum in soybean nodules with more effective strains offers the possibility of enhanced N₂ fixation in soybean (Glycine max (L.) Merr.). Our objective was to determine whether the wild soybean (G. soja Sieb. & Zucc.) genotype PI 468397 would cause reduced competitiveness of important indigenous B. japonicum strains USDA 31, 76, and 123 and thereby permit nodulation by Rhizobium fredii, the fast-growing microsymbiont of soybean. In an initial experiment, PI 468397 nodulated and fixed moderate amounts of N₂ with USDA 31 and 76 but, despite the formation of nodules, fixed essentially no N₂ with USDA 123. In contrast, PI 468397 formed a highly effective symbiosis with R. fredii strain USDA 193. In two subsequent experiments, Williams soybean and PI 468397 were grown in a pasteurized soil mixture or in soybean rhizobium-free soil and inoculated with both USDA 123 and USDA 193. In each experiment, more than 90% of the nodules of Williams contained USDA 123, while only a maximum of 2% were occupied with USDA 193. In contrast, in the two experiments, 16 and 11%, respectively, of the nodules produced on PI 468397 were occupied by USDA 123, while in both experiments 87% contained USDA 193. Thus, in relation to the cultivar Williams, which is commonly grown and used as a parent in soybean breeding programs in the United States, PI 468397 substantially reduced the competitive ability of B. japonicum strain USDA 123 in relation to R. fredii strain USDA 193.     

Interspecies homology of nodule development genes in Rhizobium and Bradyrhizobium spp.

Abstract DNA fragments representatives of ndv A and ndv B have been used as probes against genomic DNAs from different Rhizobium and Bradyrhizobium species. ndv A and ndv B homologues were found in all species, indicating extensive conservation of these genes. All Rhizobium species show chromosomal localization of ndv A and ndv B homologues.     

Effect of Compressive Strain on Cell Viability in Statically Loaded Articular Cartilage

Physiological loading of articulating joints is necessary for normal cartilage function. However, conditions of excessive overloading or trauma can cause cartilage injury resulting in matrix damage and cell death. The objective of this study was to evaluate chondrocyte viability within mechanically compressed articular cartilage removed from immature and mature bovine knees. Twenty-three mature and 68 immature cartilage specimens were subjected to static uniaxial confined-creep compressions of 0–70% and the extent of cell death was measured using fluorescent microscopic imaging. In both age groups, cell death was always initiated at the articular surface and increased linearly in depth with increasing strain magnitude. However, most of the cell death was localized within the superficial zone (SZ) of the cartilage matrix with the depth never greater than ~ 500 μm or 25% of the thickness of the test specimen. The immature cartilage was found to have a significantly greater (> 2 times) amount (depth) of cell death compared to the mature cartilage, especially at the higher strains. This finding was attributed to the lower compressive modulus of the immature cartilage in the SZ compared to that of the mature cartilage, resulting in a greater local matrix strain and concomitant cell surface membrane strain in this zone when the matrix was compressed. These results provide further insight into the capacity of articular cartilage in different age groups to resist the severity of traumatic injury from compressive loads.     

Differentiating Indigenous Soybean Bradyrhizobium and Rhizobium spp. of Indian Soils

Soybean is extensively cultivated worldwide and is the largest source of biologically fixed nitrogen among legumes. It is nodulated by both slow and fast growing rhizobia. Indigenous soybean rhizobia in Vertisols of central India were assessed for utilization of 35 carbon sources and intrinsic resistance to 19 antibiotics. There was greater utilization of trehalose and raffinose by fast growers (87 and 73 % by fast vs. 35 and 30 % by slow growers); but slow growers had higher ability to utilize glucosamine (75 % by slow vs. 33 % by fast growers). A larger proportion of slow growers were resistant to vancomycin, polymyxin-B and rifampicin (70, 65 and 55 %) compared to fast growers (13, 7 and 7 % each). Among the two 16S rRNA sequence types in the slow growers, those belonging to Bradyrhizobium spp. utilized glucosamine while those belonging to Rhizobium radiobacter did not. All the fast growers had 16S rRNA homology to R. radiobacter and majority could not utilize glucosamine. It is suggested that during initial isolations and screening of rhizobia in strain selection programmes, using carbon sources like glucosamine and antibiotics like vancomycin, polymyxin-B and rifampicin in the media may provide a simple way of distinguishing Bradyrhizobium strains from R. radiobacter among the slow growers.