Modification of the genetic effect of N-nitrosoethylurea in inbred mice by para-aminobenzoic acid

The ability of para-aminobenzoic acid--vitamin (PABA) to influence the sensitivity of mice to alkylating mutagens was studied. PABA had no influence on the cytogenetic effect of thio-TEPA. It was determined that PABA altered the effect of N-ethyl nitrosourea (ENU). The direction of modification depends on animal genotype: pre-treatment with PABA decreases the frequency of chromosome aberrations in bone marrow cells of CBA/LacY and C57BL/JY mice, but significantly increases it in 101/HY mice. The PABA influence on the frequency of gene mutations induced by ENU in melanocytes of mice and revealed by "spot-test" was not determined.     

Theoretical evaluation of necessity of carbon dioxide assimilation by microorganisms during growth on various substrates

The biological role of exogenous carbon dioxide during substrate assimilation with a various degree of reductivity is evaluated. The investigation of metabolic pathways of carbon dioxide incorporation into the metabolic processes of methaneoxidizing bacteria shows that the HCO3- ion assimilation is catalyzed by phosphoenolpyruvate carboxylase and in certain strains also by the key enzyme of autotrophic pathway of the carbon dioxide assimilation, ribulose-1,5-diphosphate carboxylase. The theoretical calculations and experimental studies indicate that exogenous carbon dioxide is a necessary participant of the metabolic processes of methane or methanol assimilation. It is also an acceptor of the excess electrons of these compounds. It is the degree of reductivity of the substrate metabolized that determines the activity of the exogenous carbon dioxide fixation by microorganisms. The carbon dioxide fixation by heterotrophic microorganisms must be considered, therefore, as a process which is mostly due to the elementary composition of the source of carbon under conversion.     

Clastogenic effect of thiophosphamide in spermatogonia of inbred strains of mice

Sensitivity of spermatogonia of 11 mouse inbred strains to induction of chromosome damages by thiophosphamide (thioTEPA) was studied. Metaphase chromosome preparations were made 24 h after treatment with thioTEPA (at 2.25 mg/kg, i/p). With respect to frequency of cells with chromosome damages, strains were ranked as follows: A/Sn (17.5 + 4.4%) greater than 101/H greater than TPS greater than WR = C57BL/6 = AKR = NZB greater than CBA/Lac greater than C3H/Sn greater than MRL greater than BALB/c (5.0 + 2.2%). This distribution does not coincide with that for sensitivity of bone marrow cells, though the data support, in general, the estimations obtained earlier for strains' mutability. Comparison of the data presented with those from literature demonstrates that the sensitivity to clastogenic effect of thioTEPA (and other alkylating agents) correlates neither with spontaneous level of SCE, nor with unscheduled DNA synthesis, nor with radiosensitivity of inbred mice. The frequency of induced chromosome aberrations in spermatogonia is relatively low and spermatogonia cannot substitute bone marrow cells as a test system when assaying chemical mutagens.     

Cytogenetic effect of mitomycin C and cytosine arabinoside on mice of different genotypes]

Cytogenetic effect of mitomycin C (MC) and cytosine arabinoside (CA) on bone marrow cells of male mice of the strains 101/HY, C57BL/6Y C,3H/SnY and of the (C3HX101) F1 hybrids was studied. The frequencies of cells with chromosome aberrations after the treatment with MC at a 5 mg/kg dose were 54,4%; 41,8%; 40,4% and 26,8% in 101H, B6, C3H/Sn mice and in the F1 hybrids (C3HX101) respectively. The frequencies of cells with chromosome aberrations after the treatment with CA at a 500 mg/kg dose were 25,2%; 17,8%; 10,8% and the 101/H, B6, C3H/Sn mice and in the F1 hybrids (C3HX101) respectively. Both mutagens induced the greatest number of chromosome aberrations in the 101/H strain and the smallest number in the F1 hybrid (C3HX101). A positive correlation was established between the levels of induced and spontaneous chromosome lesions.     

Subordination of the taxa of gram-negative bacteria determined by numerical analysis methods

Various numerical methods were used to estimate the coordination of taxa of gram-negative aerobic and facultative anaerobic organoheterotrophic and chemolithotrophic bacteria. Stable phena were found to be formed by cultures belonging to the families Rhizobiaceae, Halobacteriaceae, Enterobacteriaceae, Nitrobacteriaceae (except the genus Nitrobacter), and Methylomonadaceae (except the genus Methylococcus). The unstable position was found in the genera Thermus, Zoogloea, Xanthomonas, Sulfolobus, Methylococcus, Alcaligenes, Brucella, and Acetobacter. The greatest scatter among the objects being analysed was detected among genera belonging to the family Pseudomonadaceae. The taxonomic position of these genera must be defined more precisely. The family Methylomonadaceae is related to such physiologically unique groups of microorganisms as nitrifying, sulfate-reducing, extreme thermophilic and halophilic forms. All in all, the data reported in this work show that numerical analysis can be used to specify the classification structure of bacteria. In a number of cases, the results are consistent with those changes which are performed in the Bergey Manual 9 using logical analysis (for instance, concerning the position of the genera Gluconobacter, Acetobacter, Beijerinckia, and Derxia).     

Modeling the periodically-changing predictable response to mutagen exposure in CBA/LacY mice in a successive inbred generations]

A hypothesis on the genetic determination of periodic fluctuations of the sensitivity to the mutagen thioTEPA in successive inbred generations of mice has been earlier put forward. This study was the initial stage of testing this hypothesis. The mouse strain CBA/LacY was divided into two substrains, which differed in the rate of generation change. As a result, two colonies of isogenic mice differing by 10-12 generations with respect to the inbred age were obtained. Both the rate and range of variations in the mutagen sensitivity (four generations per period of the cycle and 20-40% of cells with chromosome aberrations after the standard dose of 2.5 mg/kg of thioTEPA, respectively) in 19 generations of the "fast" substrain agreed with earlier data. The response of the "slow" substrain corresponded to the expected response of the "fast" substrain after the given number of generations. In the mice of generations F142 and F146 that lived simultaneously and differed in thioTEPA sensitivity, the effects of the carcinogen benzo[a]pyrene (BaP) were significantly different. The levels of these effects corresponded to the levels of the responses to thioTEPA. The data obtained agree with the hypothesis tested.     

Processes of plant colonization by Methylobacterium strains and some bacterial properties

The pink-pigmented facultative methylotrophic bacteria (PPFMB) of the genus Methylobacterium are indespensible inhabitants of the plant phyllosphere. Using maize Zea mays as a model, the ways of plant colonization by PPFMB and some properties of the latter that might be beneficial to plants were studied. A marked strain, Methylobacterium mesophilicum APR-8 (pULB113), was generated to facilitate the detection of the methylotrophic bacteria inoculated into the soil or applied to the maize leaves. Colonization of maize leaves by M. mesophilicum APR-8 (pULB113) occurred only after the bacteria were applied onto the leaf surface. In this case, the number of PPFMB cells on inoculated leaves increased with plant growth. During seed germination, no colonization of maize leaves with M. mesophilicum cells occurred immediately from the soil inoculated with the marked strain. Thus, under natural conditions, colonization of plant leaves with PPFMB seems to occur via soil particle transfer to the leaves by air. PPFMB monocultures were not antagonistic to phytopathogenic bacteria. However, mixed cultures of epiphytic bacteria containing Methylobacterium mesophilicum or M. extorquens did exhibit an antagonistic effect against the phytopathogenic bacteria studied (Xanthomonas camprestris, Pseudomonas syringae, Erwinia carotovora, Clavibacter michiganense, and Agrobacterium tumifaciens). Neither epiphytic and soil strains of Methylobacterium extorquens, M. organophillum, M. mesophilicum, and M. fujisawaense catalyzed ice nucleation. Hence, they cause no frost injury to plants. Thus, the results indicate that the strains of the genus Methylobacterium can protect plants against adverse environmental factors.     

Soil drying as a model for the action of stress factors on the natural bacterial population

The drying of soil samples reduced the abundance (especially of predominant species) and the diversity of bacteria isolated from these samples, making easier the isolation of rare bacterial species. Some bacterial species that were minor before soil drying became dominant in dried soil samples. In general, soil drying allowed the diversity of soil bacteria to be determined more adequately. The bacteria that were isolated from dried soil samples turned out to be resistant to gamma radiation (with LD90 = 2.8-4.6 kGy) and desiccation. It is concluded that soil drying may serve as a model for the action of stress factors on natural bacterial populations. The hypothesis that periodic desiccation was the primary cause of formation of bacterial radioresistance in nature is discussed.     

The Effect of γ-Radiation and Desiccation on the Viability of the Soil Bacteria Isolated from the Alienated Zone around the Chernobyl Nuclear Power Plant

Methylobacterium extorquens, M. mesophilicum, and Bacillus subtilis strains were found to be resistant to -radiation, irrespective of whether they were isolated from the alienated zone around the Chernobyl Nuclear Power Plant or outside this zone. The LD₉₀ of Methylobacterium and B. subtilis strains with respect to -radiation was 2.0–3.4 and 3.7–4.4 kGy, respectively, whereas their LD_99.99 values were 4.5–6.9 and more than 10 kGy, respectively. The high threshold levels of -radiation for Methylobacterium and B. subtilis imply the efficient functioning of DNA repair systems in these bacteria. Unlike Bacillus polymyxa cells, the cells of M. extorquens, M. mesophilicum, and B. subtilis were also resistant to desiccation. Pseudomonas sp., Nocardiasp., and nocardioform actinomycetes were sensitive to both -radiation and desiccation. Similar results were obtained when the bacteria studied were exposed to hydrogen peroxide and ultraviolet radiation. The results obtained indicate that the bacteria that are resistant to -radiation are also resistant to desiccation, UV radiation, and hydrogen peroxide. The possibility of using common laboratory tests (such as the determination of bacterial resistance to UV light and desiccation) for the evaluation of bacterial resistance to -radiation is discussed.     

Ribosomal genes in inbred mouse strains: interstrain and intrastrain variations of copy number and extent of methylation

Quantitative dot hybridization was used to estimate the rDNA copy number in brain tissues of five inbred mouse strains (AKR/JY, NZB/B1OrlY, CBA/CaLacY, 101/HY, and 129/JY), which were obtained from the collection of the Research Center of Biomedical Technologies (Y). In each strain, 9-12 mice aged 1-2 months were examined. The rDNA copy number per diploid genome in strains AKR (range 105-181, mean +/- SD 136 +/- 27) and NZB (129-169, 148 +/- 12) was significantly lower than in strains CBA (172-267, 209 +/- 31), 101 (179-270, 217 +/- 30), and 129 (215-310, 264 +/- 33). Mice of strain NZB were relatively homogeneous in this trait (CV = 8.1%). Strains AKR, CBA, 101, and 129 displayed significant between-group differences, CV varying from 12.5 to 19.9%. The same DNA specimens were digested with MspI or HpaII and used to estimate the extent of methylation of the 28S rDNA region. Regardless of the strain, all mice could be classed into two groups. One group (20 mice) had a methylated fraction accounting for less than 8% of rDNA and included all nine mice of strain NZB, seven out of nine mice of strain 101, and three out of ten mice of strain 129. In the other group (29 mice), the methylated fraction varied from 18 to 38%. A possible role of methylation and the genome dosage of ribosomal genes in phenotypic variation (quantitative trait variation) of inbred mouse strains is discussed.