Regulation of Nitrogenase Synthesis by Oxygen in Klebsiella pneumoniae

Klebsiella pneumoniae does not fix N₂ under aerobic conditions. The two protein components required for nitrogenase activity were studied during aeration of cells in nitrogen-free media. Component II of nitrogenase was inactivated more slowly in vivo than component I during aeration. The rate of loss of component II was less than the rate of component II synthesis during derepression. No inactive components were detected in cells that had been growing on NH₄⁺ and then aerated in nitrogen-free medium. This supports the hypothesis that O₂ somehow represses the formation of nitrogenase.     

Internal Membrane Control in Azotobacter vinelandii

Azotobacter vinelandii was grown on N(2), NH(4) (+), or NO(3) (-), and an internal membrane network was observed by electron microscopy of thin sections of cells. Cells obtained in early exponential growth contained less internal membrane than did cells from cultures in late exponential growth. It seems likely that O(2) has a role in regulating the amount of internal membrane structure.     

Interleukin 1-driven secretion of interleukin 2 is highly temperature-dependent

To investigate the temperature dependence of T lymphocyte activation, we have examined the IL 1-induced secretion of IL 2 by the murine T lymphoma cell line LBRM-33-1A5. During 24-hr incubations, there are modest increases in IL 2 secretion as culture temperatures are increased from 33 degrees to 37 degrees C, but IL 2 secretion declines at higher temperatures. However, the kinetics of IL 2 release during the first 8 hr of culture are highly temperature-dependent. The rate of IL 2 release increases linearly with temperature over the range from 33 degrees to 41 degrees C, demonstrating temperature coefficients (Q10) greater than 70. In contrast, IL 2-promoted proliferation of a continuous T cell line is much less temperature-dependent with Q10 values of less than 4.0.     

Use of Two-Dimensional Polyacrylamide Electrophoresis to Demonstrate that Putative Rhizobium Cross-Inoculation Mutants Actually Are Contaminants

Two-dimensional polyacrylamide electrophoresis was used to determine that mutants of Rhizobium trifolii DT6, claimed to be capable of effectively nodulating soybeans, were actually Rhizobium japonicum 110 contaminants isolated from the parent DT6 culture.     

Feedback inhibition of nitrogenase.

No inhibition of nitrogenase activity by physiological levels of NH4+ or carbamyl phosphate was observed in extracts of Azotobacter vinelandii. All of the 15N2 reduced by cultures which received no NH4+ was found in the cells. By contrast, more than 95% of the 15N2 reduced by cultures which had been given NH4+ was found in the medium. Failure to examine the culture medium would lead to the erroneous conclusion that N2 fixation is inhibited by NH4+. Nitrogenase in a derepressed mutant strain of A. vinelandii was fully active in vivo in the presence of NH4+. The addition of NH4Cl to N2-fixing cultures resulted in no decrease in the N2-reducing activity of intact cells of Klebsiella pneumoniae or Clostridium pasteurianum and only a small (15%) decrease in A. vinelandii. Therefore, no significant inhibition of nitrogenase by NH4+ or metabolites derived from NH4+ exists in A. vinelandii, K. pneumoniae, or C. pasteurianum.     

Host recognition in the Rhizobium-soybean symbiosis

Polar binding of Rhizobium japonicum to roots and root hairs of Glycine soja (L.) Sieb. and Zucc. is specifically inhibited by d-galactose and N-acetyl-d-galactosamine, haptens of Glycine max seed lectin. A protein, immunologically cross-reactive with the G. max seed lectin, is present in G. soja seed extracts. Peptide mapping of the purified G. max and G. soja lectins indicates that the two are similar in structure. Soybean lectin can be localized on the surface of both G. max and G. soja roots by indirect immunolatex techniques. These observations indicate that the Rhizobium-binding lectin, previously isolated from seeds, also is present on the root surface-the site of the initial steps in the infection. This lectin is capable of binding Rhizobium japonicum to the root.     

Diversity and Dynamics of Indigenous Rhizobium japonicum Populations

A simple method, based upon the separation of cellular proteins by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, has been devised for distinguishing between isolates of Rhizobium japonicum. Eleven laboratory strains, previously classified into five serogroups, were analyzed by gel electrophoresis. Groups determined subjectively according to protein patterns matched the serogroups, with one exception. Most strains within serogroups could be distinguished from one another. For studying the ecology of Rhizobium, an important advantage of this technique compared with serology or phage typing is that it discriminates among previously unencountered indigenous bacterial isolates as well as among known laboratory strains. SDS-gels were used to analyze the Rhizobium population of 500 nodules, sampled throughout the growing season, from soybeans at two different Wisconsin localities. Although the soybeans had been inoculated with laboratory strains of R. japonicum, indigenous R. japonicum predominated. At one location, 19 indigenous gel types were distinguished and classified mainly into four groups. At the other location, 18 gel types, falling mainly into three groups, were detected. The predominance of a particular group varied, in some cases dramatically, depending upon the time and depth of nodule formation.