The Ways of Plant Colonization by MethylobacteriumStrains and Properties of These Bacteria

The pink-pigmented facultative methylotrophic bacteria (PPFMB) of the genus Methylobacteriumare indispensible inhabitants of the plant phyllosphere. Using maize Zea maysas 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 mesophilicumAPR-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. mesophilicumAPR-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. mesophilicumcells 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 mesophilicumor M. extorquensdid exhibit an antagonistic effect against the phytopathogenic bacteria studied (Xanthomonas campestris, Pseudomonas syringae, Erwinia carotovora, Clavibacter michiganense,andAgrobacterium tumifaciens). Neither epiphytic nor soil strains of Methylobacterium extorquens, M. organophillum, M. mesophilicum, andM. fujisawaensecatalyzed ice nucleation. Hence, they cause no frost injury to plants. Thus, the results indicate that the strains of the genus Methylobacteriumcan protect plants against adverse environmental factors.     

Comparison of three inbred lines of mice by overall and genetic radiosensitivity

The radiosensitivities of three mouse strains (BALB/cLacY, C3H/SnY, and 101/HY) have been compared using the following parameters: survival after irradiation at a dose of 6-7 Gy, chromosome aberration frequency in bone marrow cells after irradiation at a dose of 1.5 Gy, and the change in testis weight and frequency of abnormal sperm heads (ASHs) after irradiation at doses from 0.5 to 4 Gy. Strain BALB/c is the most radiosensitive with respect to the survival and chromosome aberration frequency in the bone marrow but the most resistant with respect to the change in testis weight and the frequency of abnormal sperm heads. Strain 101/HY was the most resistant with respect to survival and chromosome aberration frequency in bone marrow after irradiation but the most radiosensitive with respect to testis damage.     

Effects of para-aminobenzoic acid on radiosensitivity of mice of different strains

The aim of the work was to study the possible protective effect of para-aminobenzoic acid (PABA) on the radiation lethality in mice of three inbred lines (BALB/cLacY, C3H/HeY, 101/Hy), stock YT1 and hybrids (C3H/He x 101/H)F1. The PABA solution was given to the mice intraperitoneally in single doses of 10, 50 and 100 mg/kg 40-50 min prior to irradiation with doses of 6 to 8 Gy depending on the line and sex of mice. The used doses of gamma-radiation were roughly LD75/30. The radioprotective effect of PABA was observed in all variants of the experiment but it was relatively low. The protection coefficient varied from 0 to 0.45. The protective effect depended on the line and sex of mice and on the dose of the injected substance.     

Peculiarities of ethanol metabolism in an Acinetobacter sp. mutant strain defective in exopolysaccharide synthesis

Activities of the key enzymes of ethanol metabolism were assayed in ethanol-grown cells of an Acinetobacter sp. mutant strain unable to synthesize exopolysaccharides (EPS). The original EPS-producing strain could not be used for enzyme analysis because its cells could not to be separated from the extremely viscous EPS with a high molecular weight. In Acinetobacter sp., ethanol oxidation to acetaldehyde proved to be catalyzed by the NAD(+)-dependent alcohol dehydrogenase (EC 1.1.1.1.). Both NAD+ and NADP+ could be electron accepters in the acetaldehyde dehydrogenase reaction. Acetate is implicated in the Acinetobacter sp. metabolism via the reaction catalyzed by acetyl-CoA-synthetase (EC 6.2.1.1.). Isocitrate lyase (EC 4.1.3.1.) activity was also detected, indicating that the glyoxylate cycle is the anaplerotic mechanism that replenishes the pool of C4-dicarboxylic acids in Acinetobacter sp. cells. In ethanol metabolism by Acinetobacter sp., the reactions involving acetate are the bottleneck, as evidenced by the inhibitory effect of sodium ions on both acetate oxidation in the intact cells and on acetyl-CoA-synthetase activity in the cell-free extracts, as well as by the limitation of the C2-metabolism by coenzyme A. The results obtained may be helpful in developing a new biotechnological procedure for obtaining ethanol-derived exopolysaccharide ethapolan.     

Modeling of Periodically Changing Predictable Response to Mutagens in Successive Inbred Generations of CBA/LacY Mice

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 will be 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 F₁₄₂and F₁₄₆that 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.     

Cytogenetic analysis of thioTEPA-induced translocations in the spermatids of male mice

Spermatocytes of 36 reciprocal translocation heterozygotes at diakinesis-MI stage were studied cytogenetically. There were 38.8 % cells with rings and 32.8 % - with chains and univalents among 3666 cells. It is concluded that intensive mutational process producing 30 % of translocation heterozygotes is characterized by random breakage along the chromosomes.     

Morphofunctional characteristics of the reproductive system in female mice of the mutant strain B10-hr rhY

The long duration of the estrous cycle, the absence of the ovulated oocytes was observed in histomorphological studies of estrous cycles and ovaries in hr rhY-/hr rhY-mutants of B10-hr rhY mice strain. The absence of mutation division, ovulation and corpora lutea in ovaries was found in contrast to normal isogenic B10 females. The extragonadal cause of hairless mutant female infertility was shown. The effective method of mutant strain B10-hr rhY reproduction by using the transplantation of homozygous hairless female ovaries to isogenic recipients (+/+ or +/hr rhY) was proposed.     

Histological study of oogenesis pathology in smoky mutant mice

The various pathology of female mice reproductive system with the mutation smoky (smk) was observed. This recessive autosomal gene dilutes the black colour of hair to the light smoky. The cases with ovarian agenesis and dysgenesis of the mutants WR-smk/smk and B6-smk/smk without the germ cells or with the acute deficit was discovered. The oogenesis pathology of the mutants B6-smk/smk was revealed by the block of oocyte growth and their nucleus development in the growing nonatretic follicles leading to the female infertility. Endogene causes of the female hypogonadism and infertility associated with the mutation smoky are proposed.     

Cellular effects of functional unloading and passive strain of soleus muscle in dystrophin-deficient mice

There is a suggestion that dystrophin, a subsarcolemmal protein communicating fiber cytoskeleton to extracellular matrix, participates in signal transduction reflecting the mechanical state of skeletal muscle (mechanotransduction). Recent works indicate the possible signaling role of this protein in the prevention of the activation of proteolytic processes accompanying development of muscle fiber atrophy and in realization of anabolic effects of muscle passive stretching. To assess the role of dystrophin in these processes, the experiment was carried out on two-month old C57 black and mdx (dystrophin-deficient) mice subjected to hind-limb suspension with stretching and without it. Passive stretching results in the partial prevention of atrophy in two muscle fiber types of both C57 black and mdx mice; at the same time, in mdx mice, the slow-to-fast transformation of the soleus muscle fiber type was not observed. Proliferative activity in soleus muscle decreased as a result of hind-limb suspension, but markedly increased during muscle passive stretching. We have found no correlation between the altered dystrophin synthesis and proliferative activity of satellite cells during hind-limb suspension and hind-limb suspension with stretching. Hence, the disturbed dystrophin synthesis retards the atrophy of slow muscle fibers and practically does not affect the stretching preventive action.     

Estimation of the contribution of thiophosphamide-induced chromosomal aberrations to perimplantation embryonic mortality in mice]

Thiotepa-induced perimplantation mortality in mice was analysed cytologically. The contribution of induced chromosomal aberrations to preimplantation embryonic death was studied. Under the influence of 1.25 mg/kg of thiotepa on late spermatids the stop of cleavage division was found at 2--16 cell stage in 27% of the cases and at 17--22 cell stage in 11.9% (totally in 38.9%) as compared to 6% in the controls. The cytogenetic analysis of embryos consisting of 2--16 cells revealed gross structural chromosomal aberrations in 75% metaphases suitable for analysis.