The mutagenic effect of hydroxylamine onMycobacterium phlei strain PA

The mutagenic effect of 0.05m and 1m HA onMycobacterium phlei PA was investigated. To establish the mutagenic effect the inactivating effect was studied under the same experimental conditions. Hydroxylamine at a higher concentration (1m) exhibited relatively high mutagenic effect. This was indicated by about 100-fold and 10-fold higher frequency of INH^r and STM^r mutants, respectively (as compared with spontaneous mutations) and induction of auxotrophic mutants. On the other hand, the mutagenic effect of 0.05m hydroxylamine was low under the same experimental conditions. The inactivating effect of a higher HA concentration (1m under given experimental conditions) was considerably higher when using the given model microorganism than that of the lower one (0.05m under the same experimental conditions). This finding does not agree with literature data obtained in other experimental models.     

The mutagenic effect of ultraviolet radiation and nitrous acid onMycobacterium phlei

Lethal and mutagenic effects of nitrous acid and UV radiation onMycobacterium phlei were studied Three auxotrophic strains of the PA strain ofMycobacterium phlei were obtained: ala^-, his^-, and gly^- (ser^-) INH^r Bods of the his^- strain grown in liquid media are longer to filamentous as compared with cells of the prototrophic PA strain grown in the same media, whereas cells of the gly^- (ser^-) INH^r mutant are shorter to coccobacillary. Cells of the ala^- strain are characterized by their various length from normal to coccobacillary. The auxotrophic strains obtained differ from each other by a frequency of spontaneous reversions to prototrophy. The his^- strain is the most stable, a frequency of spontaneous reversions to prototrophy being 10^-9. The gly^- (ser^-) INH^r strain reverts spontaneously to prototrophy with a frequency of 10^-8 to 10^-7. The ala^- strain spontaneously reverting with a frequency of 10^-5 is the most labile. The auxotrophic mutants obtained do not differ from the original prototrophic strain in the other properties studied. A change in a frequency of INH and STM-resistant mutants was also studied. It was found that under the influence of UV radiation a frequency of INH-resistant mutants increases 43 to 80 fold as compared with a frequency of spontaneous mutations, this latter being about 2.6 × 10^-6. No substantial increase in a frequency of STM-resistant mutants was found using UV irradiation under the given experimental conditions; their spontaneous frequency equals to 9.0 × 10^-9 to 2.0 X 10^-8.     

Mutagenic effect of N-Methyl-N-nitrosourea onMycobacterium phlei

N-Methyl-N-nitrosourea was used to induce auxotrophic, scotochromogenic and isonicotinic acid hydrazide resistant mutants inMycobacterium phlei and its effect was compared with that of nitrosoguanidine. Seventeen auxotrophic mutants requiring arnino acids or vitamins and 52 sootochromosgenic mutants with orange colonies were induced. The frequency of isonicotinic acid hydrazide-resistant mutants increased by two orders of magnitude.     

The mutagenic effect of ethyl methanesulfonate on a non-acid-fast strain ofMycobacterium phlei

Ethyl methanesulfonate was used for the induction of three types of mutants in a non-acidfast strain ofMycobacterium phlei. A total of 20 auxotrophie mutants was isolated. The mutants were isolated mostly when using doses yielding higher survival of the cells of the basic suspension. The auxotrophic mutants isolated required mostly amino acids, two mutants required purines and three mutants required vitamins. By determining the frequency of spontaneous reversions, it was found that 9 auxotrophic mutants could be used for further genetic studies. These included the following phenotypes: isoleucine⁻, leucine⁻, lysine⁻, nicotinic acid⁻, pyridoxine⁻, and xanthine⁻. Seven scotochromogenic mutants were isolated after ethyl methanesulfonate treatment. One was ochre, the remaining six were orange. Six achromogenic mutants were detected. Spontaneous auxotrophic mutants, scotochromogenic and achromogenic mutants were not isolated. The treatment with 0.2m ethyl methanesulfonate resulted in an increase in the frequency of STM-resistant mutants, the maximum phenotypic expression taking place after 72 hours cultivation in a liquid medium without the drug. The frequency of induced STM-resistant mutants varied within the range of 8.6.10⁻⁵–1.0.10⁻⁴ as compared with the frequency of spontaneous mutants 5.8.10⁻⁶–8.8.10⁻⁶.     

The effect of rifampicin onMycobacterium smegmatis

Rifampicin was found to inhibit the growth and incorporation of¹⁴C-adenine,¹⁴C-leucine and¹⁴C-glycine in exponentially growing cells ofM. smegmatis cultivated in Merrill’s synthetic medium. Increasing concentrations of the antibiotic inhibited respiration in resting cells, in the presence of glucose or 2-oxoglutarate as substrates in particular. In addition to the well-known interference of rifampicin with the biosynthesis of RNA, the effect on the energy metabolism should also be considered.     

The use of nitrosoguanidine in the study of mutagenesis in a non-acid-fast strain ofMycobacterium phlei

N-methyl-N-nitroso-N′-nitroguanidine was used for the induction of two types of mutations in the PN strain ofMycobacterium phlei. Nineteen auxotrophic, 136 scotochromogenic and 50 achromogenic mutants were isolated after of treatment with nitrosoguanidine at a concentration of 1,000 μg/ml. Auxotrophic mutants required primarily amino acids and vitamins and half of them may be used for further genetic work due to their low frequency of spontaneous reversions. Colonies of scotochromogenic mutants were orange with the exception of one, which was strawberry red. Most scotochromogenic mutants were detected on a streptomycin containing medium. Roughly two thirds of the scotochromogenic mutants and one half of achromogenic mutants did not revert to the original photochromogenic character.     

Lethal and mutagenic effects of nitrosoguanidine on synchronizedChlamydomonas

Summary The lethal and mutagenic effects of 5 g/ml N-methyl-N-nitro-N-nitrosoguanidine (MNNG) were maximal during the nuclear S-period of synchronously grownChlamydomonas reinhardtii. This was revealed by a 50% drop in survival and a 50- to 100-fold increase in the recovery of slow-growth mutants (up to 40% of the survivors) which were first recognized as small colonies on agar medium. Partial characterization of these isolates revealed about 50% to be stable on subculture, and several were demonstrated to be either acetate-dependent, dark-lethal (light-dependent), or acetate-sensitive mutants. There was no significant increase of lethality or of slow-growth mutants correlated with treatment during the chloroplast DNA replication phase of the cell-cycle.The results of genetic analysis with 13 mutants induced during the nuclear S-period were consistent with their nuclear origin. These analyses were hampered by the high proportion of lethality among the progeny of most crosses.It is concluded that the enhanced mutant induction among nuclear S-phase cells may indicate preferential mutagenesis of replication fork DNA and induction of multiple-closely-linked mutations, as in some bacteria. Consequently, forC. reinhardtii, caution should be exercised in drawing relationships between abnormal behavioral and biochemical phenotypes in MNNG-induced mutants.     

The effect of nitrosoguanidine upon DNA synthesis in vitro

Summary Both the polymerase and the exonuclease activities of DNA polymerase III^* are inactivated by treatment with nitrosoguanidine. The treatment of the DNA template with the mutagen does not affect the template in supporting DNA synthesis. No effect of nitrosoguanidine upon fidelity of replication in vitro was detected.     

The use of ethyl methanesulfonate for the induction of mutants inMycobacterium phlei PA

The mutagenic effect of ethyl methanesulfonate in a concentration of 0.2m on a prototrophic, acid-fast strainMycobacterium phlei PA was studied by following the induction of changes of three genetic markers: prototrophy to auxotrophy and sensitivity to two antituberculosis drugs (INH and STM) to resistence. Ethylmethanesulfonate was found to be a very effective mutagen in all three cases. Thirty auxotrophic strains were obtained, out of which eight exhibited a low frequency of spontaneous reversions and could hence be used for further studies. Of the phenotypes induced the glycine⁻ (serine⁻) type was most frequently isolated and represented more than half of all auxotrophs obtained. Requirements for lysine and purines were also observed. The EMS treatment (1% survival of the basic suspension) resulted in a 74-fold increase of the frequency of INH-resistant mutants and a frequency of STM-resistant mutants about 1.1/2 to almost 2 orders of magnitude higher than the spontaneous values     

The effect of nitrosoguanidine on carotene-synthesizing and pigment-free yeasts

A number of mutants with a demand for amino acids, vitamins and nitrous bases has been obtained under effect of nitrosoguanidine (0.05%) on the yeast Candida utilis and carotene-synthesizing yeast Rhodosporidium diobovatum, Rhodotorula glutinis var. glutinis and Rh. rubra. Concentration of auxotrophs due to the death of prototrophs has been achieved in the studied yeast, with the exception of Rh. rubra using additional treatment by levorin (200 units/ml). When selecting quickly growing mutants of carotene-synthesizing yeast obtained after treatment by nitrosoguanidine, the primary selection by the intensity of red-orange colour of the colonies proved to be more efficient than that by resistance to monoiodoacetic acid. The selected mutants of the pigmented yeast surpassed by primary culture as to the harvest of carotenoids (including beta-carotene) and biomass in the periodic and continuous processes.     

The increasing mutagenic effect of nitrosoguanidine under the influence of modified bases during inhibition of repair AGT enzyme in mammalian somatic cells in vitro

Gene mutations were studied on human cells SL68, XP12BE and chinese hamster cells Blld-ii-FAF28C1237. All the cells were sensitive to purine base analogs and were characterized by a high rate of O6-alkylguanine-DNA-transferase (AGT) activity. Inhibiting AGT activity by O6-benzylguanine considerably increases the frequency of mutants induced by the alkylating agent MNNG. Transitions of the GC-->AT type are the dominant mutations in the coding region of the hprt gene. The mechanism of DNA lesion repair by the AGT enzyme differs significantly from the excision repair.     

The mutagenic effect of beryllium on animals

Experiments on animals have revealed that beryllium in toxic dose induces lesions of chromosomes in the bone marrow cells mostly because of chromosome aberrations. No mutagenic effect of beryllium on sex cells has been revealed.     

The mutagenic effect of polymorphonuclear leukocytes on Yersinia pestis

As the result of in vitro experiments, Y. pestis auxotrophic mutants have been obtained under the influence of polymorphonuclear lymphocytes obtained from guinea pigs, previously immunized with Y. pestis strain EV. The mutagenic effect has been found to occur at minute 45 of phagocytosis. The control treatment of the bacteria with the lysate of neutrophils, homologous serum, penicillin (antibiotic-influenced selection) has not been found to lead to the appearance of auxotrophicity. These data suggest that the polymorphonuclear leukocytes of animals, having a set of powerful cytocidal systems, play an active role in the process of the natural variability of Y. pestis.