Codon usage bias in radioresistant bacteria.

The relationship between patterns of codon usage bias (CUB), the preferential usage of synonimous nucleotide triplets encoding the same amino acid, and radioresistance was investigated int he genomes of 16 taxonomically distinct radioresistant prokaryotic organisms and in a control set of 11 non-radioresistant bacteria. The radioresistant species were found to be strongly biased towards G and C in the third synonimous codon position. ENC and neutrality plots also sugest that CUB in radioresistant bacteria is mainly affected by mutational bias. Furthermore, the availability of tRNA gene copy number was analyzed and it was found that nine radioresistant species have the sam number of tRNA gene copies for each codon. This suggests that tRNA gene copies and codon bias co-evolved in a specific way in radioresistant species.

Defenses against keratinolytic bacteria in birds living in radioactively contaminated areas.

Microorganisms have shaped the evolution of a variety of defense mechanisms against pathogenic infections. Radioactivity modifies bacterial communities and, therefore, bird hosts breeding in contaminated areas are expected to adapt to the new bacterial environment. We tested this hypothesis in populations of barn swallows (Hirundo rustica) from a gradient of background radiation levels at Chernobyl and uncontaminated controls from Denmark. Investment in defenses against keratinolytic bacteria was measured from feather structure (i.e., susceptibility to degradation) and uropygial secretions. We studied degradability of tail feathers from areas varying in contamination in laboratory experiments using incubation of feathers with a feather-degrading bacterium, Bacillus licheniformis, followed by measurement of the amount of keratin digested. The size of uropygial glands and secretion amounts were quantified, followed by antimicrobial tests against B. licheniformis and quantification of wear of feathers. Feathers of males, but not of females, from highly contaminated areas degraded at a lower rate than those from medium and low contamination areas. However, feathers of both sexes from the Danish populations showed little evidence of degradation. Individual barn swallows from the more contaminated areas of Ukraine produced the largest uropygial secretions with higher antimicrobial activity, although wear of feathers did not differ among males from different populations. In Denmark, swallows produced smaller quantities of uropygial secretion with lower antimicrobial activity, which was similar to swallow populations from uncontaminated areas in Ukraine. Therefore, barn swallows breeding in contaminated areas invested more in all defenses against keratinolytic bacteria than in uncontaminated areas of Ukraine and Denmark, although they had similar levels of feather wear. Strong natural selection exerted by radioactivity may have selected for individuals with higher defense capacity against bacterial infections during the 30 years since the Chernobyl disaster.

Evidence for positive selection on a number of MicroRNA regulatory interactions during recent human evolution.

MicroRNA (miRNA)-mediated gene regulation is of critical functional importance in animals and is thought to be largely constrained during evolution. However, little is known regarding evolutionary changes of the miRNA network and their role in human evolution. Here we show that a number of miRNA binding sites display high levels of population differentiation in humans and thus are likely targets of local adaptation. In a subset we demonstrate that allelic differences modulate miRNA regulation in mammalian cells, including an interaction between miR-155 and TYRP1, an important melanosomal enzyme associated with human pigmentary differences. We identify alternate alleles of TYRP1 that induce or disrupt miR-155 regulation and demonstrate that these alleles are selected with different modes among human populations, causing a strong negative correlation between the frequency of miR-155 regulation of TYRP1 in human populations and their latitude of residence. We propose that local adaptation of microRNA regulation acts as a rheostat to optimize TYRP1 expression in response to differential UV radiation. Our findings illustrate the evolutionary plasticity of the microRNA regulatory network in recent human evolution.

[Selection of active strains of Actinomadura carminata, the producer of carminomycin]. / Selektsiia aktivnykh shtammov Actinomadura carcminata--produtsenta karminomitsina.

The method of selecting active strains among a definite group of analogue-resistant mutants was used on the basis of studying the dependence of the carminomycin-producing organism growth and the antibiotic synthesis level on some metabolites. As a result, gamma-ray induced mutants 4 times more active than the parent strains were obtained.

Auxotrophic mutants in the selection of the rubomycin producer, Actinomyces coeruleorubidus. / Auksotropnye mutanty v selektsii produtsenta rubomitsina----Actinomyces coeruleorubidus.

A total of 351 auxotrophic mutants with different antibiotic activity, including several mutants with activity higher than that of the parent prototrophic strains were obtained under the effect of gamma-rays from 3 prototrophic strains of Act. coeruleorubidus. It was shown that most of the auxotrophic mutants did not preserve the property of biochemical insufficiency on passages on complete media. A mutant strain 1059-32 with activity 2 times higher than that of the prototrophic strain 2-39 and the parent auxotrophic culture was obtained from the revertants. Requirements in 29 growth factors including 17 amino acids, 4 nitrous bases, 8 vitamins and coenzymes were determined in 46 stable auxotrophic mutants isolated. The effect of the specific and non-specific growth factors on the culture antibiotic production was studied.

Effects of ancestral X irradiation followed by random mating on body weight of rats.

Effects of nine generations of 450r per generation of ancestral spermatogonial X irradiation of inbred rats on body weight were examined. After six generations of random mating (avoiding inbreeding) following the termination of irradiation, descendants of irradiated males (R) were significantly lighter than their controls (C) at 3 and 6 weeks, but not at 10 weeks of age. However, differences in growth between R and C populations were small. Among-litter and within-litter variance estimates were generally larger in the R lines than in the C lines, suggesting that selection responses would be greater in R than in C lines. In conjunction with previous evidence--obtained during the irradiation phase of the experiment--this suggested that more rapid response to selection for 6-week body weight, in particular, might accrue in the R lines.

[Mutants of Pichia guilliermondii yeasts with multiple sensitivity to antibiotics and antimetabolites. I. The selection and properties of the mutants]. / Mutanty drozhzhei Pichia guilliermondii s mnozhestvennoi chuvstvitel'nost'iu k antibiotikam i antimetabolitam. Soobshchenie I. Selektsiia i nekotorve svoistva mutantov.

Riboflavin deficient mutant Pichia guilliermondii MS1 which requires approximately 1000-fold lower concentration of exogenous vitamin B2 for growth when compared with a non-adapted riboflavin deficient mutants of this species was isolated by means of of UV-irradiation. The growth of the mutant was strongly inhibited by actinomycin D and L-canavanine. The revertant MS8 and MS14 which synthesized riboflavin were selected from the strain MS1. These revertants posses a multiple sensitivity to actinomycin D, rifamycin, euflavine, mitomycin C, antimycin A, 8-azaadenine, 8-azaguanine, L-canavanine and 7-methyl-8-trifluoromethyl-10-(1'-D-ribityl)isoalloxazine. The ability to utilized glycerol and ethanol as a sole carbon source for growth was impaired in these mutants. The mutants which can utilize glycerol were isolated from the strain MS14. Such mutants were resistant to actonomycin D. Mutation (s) which determines a multiple sensitivity and inability to utilized glycerol was recessive.

[Action of N-nitroso-N-methylbiuret on Penicillium nigricans Thom and the protective effect in UV irradiation]. / Deistvie N-nitroso-N-metilbiureta na Penicillium nigricans Thom i éffekt zashchity pri UF-obluchenii

N-Nitrozo-N-methylbiuret (NMB) in a concentration of 0.2% and exposition for 2,3,4 and 6 hours with the survival rate of the conidia of 4-25% induced slight morphological variation of the griseofulvin-producing organism and increased the variation rate with respect to the antibiotic production by 40-140%. Preliminary treatment of the conidia with NMB decreased the lethal effect of UV-rays approximately by 15-25 times. The protective range with respect to morphological variation was 10 times lower. With an increase in the toxicity of NMB its protective effect in irradiation with UV-light decreased.

[Production of active mutants of a new species of rifamycin producer resistant to specific actinophage]. / Poluchenie aktivnykh mutantov novogo vida produtsenta rifamitsina, ustoichivykh k spetsifichnomu aktinofagu

Selection of a phage-stable strain of a new species of the rifamycin-producing organism was carried out. The phage-stable mutants were selected with respect to the virulent phage 2739 isolated from a lysogenic culture of the rifamycin-producing organism. Spontaneous phage-stable mutants formed at a rate of 0.8 per cent. Most of them belonged to the morphological colony type with a decreased activity level. No shifts in variation with respect to the property of the antibiotic production were noted under the action of phage 2739. 62 per cent of the phage-stable variants isolated from the secondary growth colonies after infection with the phage were lysogenic and liberated phage 2739 to the culture fluid. Induction of mutations with MNNG, UV and gamma(Co30) rays increased the frequency of the phage-stable mutanta by 1.5 times. Active phage-resistant mutants stable to the phage because of its adsorption and liberating no phage 2739 into liquid media during its cultivation were selected.