[Effect of soil microflora on 137Cs transition to plants].

The impact of certain types of microorganisms on 137Cs transfer from the substrate into the plant was analyzed in the experiment on artificial mediums. It was found that certain types of microorganisms could either reduce or increase the ratio of 137Cs transfer from the substrate to the plant. It is shown that this property is independent of the localization of the microorganism on the surface of the root, for all the analyzed bacteria belonging to the rhizospheric group. Azotobacter chroococcum UKM B-6003 stimulated the radionuclide transfer to plants up to 1.5 times, while the best bacteria for reducing its accumulation is Burkholderia sp IMER-B1 -53 - 1.3 times in comparison with the control. It was shown that the strain Bacillus megaterium UKM B-5724 from the collection of the Institute of Microbiology and Virology of NASU has a high ability to accumulate radionuclides.

Cloning and characterization of the Azotobacter vinelandii recA gene and construction of a recA deletion mutant.

The recA gene of Azotobacter vinelandii was isolated from a genomic library by heterologous complementation of an Escherichia coli recA mutation for resistance to UV radiation. The A. vinelandii recA gene was localized on adjacent PstI fragments of 1.3 and 1.7 kb. The cloned A. vinelandii recA gene was functionally analogous to the E. coli recA gene. It was also able to complement the E. coli recA mutation for homologous recombination. A recA deletion mutant of A. vinelandii was constructed. This mutant was sensitive to DNA-damaging agents like UV rays, methyl methane sulfonate (MMS) and nalidixic acid and was deficient in homologous recombination.

UV-repair and mutagenesis in Azotobacter vinelandii. I. Repair of UV-induced damages.

UV-irradiated Azotobacter vinelandii OP cells were found to be sensitive to dark repair-inhibitors, like caffeine and acriflavine. Sensitivity to both the inhibitors started to decrease at a fast rate immediately following UV-irradiation, when incubated in Burk's broth in dark. Total insensitivity to caffeine was attained at a time that was approximately double the time of the corresponding ribonucleic acid synthesis-inhibition and less than one generation time of the unirradiated cells. Nearly at the same time the rate of loss of sensitivity to acriflavine became much slower and total insensitivity to acriflavine occurred after relatively prolonged incubation. The protein synthesis inhibitor, streptomycin, reduced UV-survival, but after a time lag. The organism did not show liquid holding recovery and its UV-survival was not affected by components of complex medium. It is proposed that A. vinelandii OP possesses at least two dark-repair pathways: pre replication (acts immediately after UV exposure and is faster) and post replication (delayed and slower) repair. The first one is inhibited by caffeine and acriflavine and the second by acriflavine and streptomycin. The latter therefore requires de novo protein synthesis after UV-irradiation and may be inducible.

UV-repair and mutagenesis in Azotobacter vinelandii. II. Repair and mutagenesis.

More numbers of mutants were isolated when UV-irradiated cells of Azotobacter vinelandii OP were treated with caffeine for a limited period of time after UV-irradiation. This is encouraging, considering the difficulty in isolating Azotobacter mutants. Post-irradiation treatment with acriflavine, however, yielded comparatively lesser number of mutants.

Hydrogen-oxidizing electron transport components in nitrogen-fixing Azotobacter vinelandii.

Membranes from N2-fixing Azotobacter vinelandii were isolated to identify electron transport components involved in H2 oxidation. We found direct evidence for the involvement of cytochromes b, c, and d in H2 oxidation by the use of H2-reduced minus O2-oxidized absorption difference spectra. Carbon monoxide spectra showed that H2 reduced cytochrome d but not cytochrome o. Inhibition of H2 oxidation by cyanide was monophasic with a high Ki (135 microM); this was attributed to cytochrome d. Cyanide inhibition of malate oxidation showed the presence of an additional, low Ki (0.1 microM cyanide) component in the membranes; this was attributed to cytochrome o. However, H2 oxidation was not sensitive to this cyanide concentration. Chlorpromazine (at 160 microM) markedly inhibited malate oxidation, but it did not greatly inhibit H2 oxidation. Irradiation of membranes with UV light inhibited H2 oxidation. Adding A. vinelandii Q8 to the UV-damaged membranes partially restored H2 oxidation activity, whereas addition of UV-treated Q8 did not increase the activity. 2-n-Heptyl-4-hydroxyquinoline-N-oxide inhibited both H2 and malate oxidation.

Azotobacter cysts: reactivation by white light after inactivation by ultraviolet radiation.

Cysts of Azotobacter vinelandii 12837 inactivated by ultraviolet radiation can be reactivated by white light. This photoreactivation mechanism is not seen in the vegetative cells of the same organism.