Adaptive mutation in Saccharomyces cerevisiae

Adaptive mutation is a generic term for processes that allow individual cells of nonproliferating cell populations to acquire advantageous mutations and thereby to overcome the strong selective pressure of proliferation-limiting environmental conditions. Prerequisites for an occurrence of adaptive mutation are that the selective conditions are nonlethal and that a restart of proliferation may be accomplished by some genetic change in principle. The importance of adaptive mutation is derived from the assumption that it may, on the one hand, result in an accelerated evolution of microorganisms and, on the other, in multicellular organisms may contribute to a breakout of somatic cells from negative growth regulation, i.e., to cancerogenesis. Most information on adaptive mutation in eukaryotes has been gained with the budding yeast Saccharomyces cerevisiae. This review focuses comprehensively on adaptive mutation in this organism and summarizes our current understanding of this issue.     

Mode of action of Saccharomyces cerevisiae in enteric methane mitigation in pigs

The objectives of this study were to determine the effect and mode of action of Saccharomyces cerevisiae (YST2) on enteric methane (CH₄) mitigation in pigs. A total of 12 Duroc×Landrace×Yorkshire male finisher pigs (60±1 kg), housed individually in open-circuit respiration chambers, were randomly assigned to two dietary groups: a basal diet (control); and a basal diet supplemented with 3 g/YST2 (1.8×10¹⁰ live cells/g) per kg diet. At the end of 32-day experiment, pigs were sacrificed and redox potential (Eh), pH, volatile fatty acid concentration, densities of methanogens and acetogens, and expression of methyl coenzyme-M reductase subunit A gene were determined in digesta contents from the cecum, colon and rectum. Results showed that S. cerevisiae YST2 decreased (P<0.05) the average daily enteric CH₄ production by 25.3%, lowered the pH value from 6.99 to 6.69 in the rectum, and increased the Eh value in cecum and colon by up to −55 mV (P<0.05). Fermentation patterns were also altered by supplementation of YST2 as reflected by the lower acetate, and higher propionate molar proportion in the cecum and colon (P<0.05), resulting in lower acetate : propionate ratio (P<0.05). Moreover, there was a 61% decrease in Methanobrevibacter species in the upper colon (P<0.05) and a 19% increase in the acetogen community in the cecum (P<0.05) of treated pigs. Results of our study concluded that supplementation of S. cerevisiae YST2 at 3 g/kg substantially decreased enteric CH₄ production in pigs.     

Bleomycin-induced mutation and recombination in Saccharomyces cerevisiae

Clinical preparations of bleomycins (BM) were tested for their recombinogenicity and mutagenicity at relatively high survival levels in the simple eucaryote, Saccharomyces cerevisiae. More than a dozen test loci or genetic intervals were assayed for bleomycin-induced mutation or recombination. Treatments of stationary phase diploid yeast routinely resulted in 25–75% inactivation. The antibiotic was mildly to very highly recombinogenic and mutagenic, with one exception. The amount of bleomycin-induced mutation, gene conversion or crossing-over depended upon the particular genetic markers assayed. The drug was also potently recombinogenic in yeast cells growing in the presence of BM. These results contrast with the finding that this antitumor agent was not mutagenic in the Salmonella/mammalian microsome mutagenicity test; possible explanations of this difference are given.     

Spontaneous mutation of leu2 in Saccharomyces cerevisiae

The data obtained indicate that spontaneous mutations in Saccharomyces cerevisiae are formed during DNA replication. With no DNA replication in the lag-period, in the stationary growth phase, spontaneous mutations are not formed in cell culture during the G1 phase of cell cycle. Experimental data show the absence of primary spontaneously occurring DNA lesion accumulation in the cell G1 phase. Spontaneous mutations of yeasts are formed in the S phase of cell cycle, apparently as DNA replication errors. It is established that the frequency of spontaneous reversions of the leu2 gene in Saccharomyces cerevisiae strain NA3-24 increases when the cells are cultivated on the culture medium with different concentrations of leucine.     

Identification of a glutaminyl-tRNA synthetase mutation Saccharomyces cerevisiae

Saccharomyces cerevisiae glutaminyl-tRNA synthetase mutants were isolated through systematic screening of tight Gln- derivatives of a leaky glutamine auxotroph. These mutations define a single nuclear gene, GLN4. The gln4-1 mutation is specific for Gln-tRNA synthetase and shows a dosage effect in heterozygous diploids. The wild-type Gln-tRNA synthetase exhibits a Km for glutamine of 25 microM; the gln4-1 mutation increases this value 20-fold. These observations strongly suggest that GLN4 encodes the Gln-tRNA synthetase.     

Mode of action of yeast toxins: energy requirement for Saccharomyces cerevisiae killer toxin.

The role of the energy status of the yeast cell in the sensitivity of cultures to two yeast toxins was examined by using 12K release from cells as a measure of toxin action. The Saccharomyces cerevisiae killer toxin bound to sensitive cells in the presence of drugs that interfered with the generation or use of energy, but it was unable to efflux 12K from the cells under these conditions. In direct contrast, the Torulopsis glabrata pool efflux-stimulating toxin induced efflux of the yeast 42K pool was insensitive to the presence of energy poisons in cultures. The results indicate that an energized state, maintained at the expense of adenosine 5'-triphosphate from either glycolytic or mitochondrial reactions, is required for the action of the killer toxin on the yeast cell.     

Bleomycin-induced mutation and recombination in Saccharomyces cerevisiae.

Clinical preparations of bleomycins (BM) were tested for their recombinogenicity and mutagenicity at relatively high survival levels in the simple eucaryote, Saccharomyces cerevisiae. More than a dozen test loci or genetic intervals were assayed for bleomycin-induced mutation or recombination. Treatments of stationary phase diploid yeast routinely results in 25--75% inactivation. The antibiotic was mildly to very highly recombinogenic and mutagenic, with one exception. The amount of bleomycin-induced mutation, gene conversion or crossing-over depended upon the particular genetic markers assayed. The drug was also potently recombinogenic in yeast cells growing in the presence of BM. These results contrast with the finding that this antitumor agent was not mutagenic in the Salmonella/mammalian microsome mutagenicity test; possible explanation of this difference are given.     

Photodynamic mutagenic action of acridine compounds on yeast Saccharomyces cerevisiae

The photodynamically produced mutagenicity and toxicity of 8 acridine compounds were compared in Saccharomyces cerevisiae under resting and growing conditions. Without irradiation none of the acridines induced respiratory-deficient ('petite') colonies, indicative of mitochondrial DNA damage, in resting cells; and only acriflavine and proflavine induced 'petites' in growing cells. Also, without irradiation none of the acridines were significantly toxic or mutagenic for nuclear DNA under resting or growing conditions. However, with irradiation, acriflavine, proflavine, acridine yellow and rivanol became effective 'petite'-inducing mutagens and highly toxic for resting cells, while acriflavine, proflavine, and acridine orange became effective nuclear mutagens for resting cells. Acridine, quinacrine and 9-aminoacridine were not at all biologically effective with irradiation for resting cells. The results presented here indicate that singlet oxygen is generated by a photodynamic mechanism when acriflavine is irradiated, and further, that acridine, quinacrine and 9-aminoacridine are ineffective photosensitizers, because they are incapable of generating singlet oxygen with irradiation.     

A temperature sensitive mitochondrial mutation of Saccharomyces cerevisiae.

A mitochondrially inherited temperature sensitive respiratory deficient mutant of yeast has been isolated. Detection of nuclear suppressor mutations indicates an interaction between the nuclear and mitochondrial genomes. A preliminary biochemical characterization is presented.     

The effect of sodium nucleinate on allergic and immunological reactions

Experiments on immunized rabbits and guinea pigs indicated that sodium nucleinate (SN) was capable of weakening or entirely eliminating anaphylactic and skin reactions of delayed type hypersensitivity to repeated administration of staphyloanatoxin, APDT vaccine. The findings on patients with the infectious form of bronchial asthma and chronic rheumatism showed that sodium nucleinate attenuated reactions to the subcutaneous administration of staphylococcal and streptococcal allergens. The treatment of patients suffering from infectious-allergic bronchial asthma and rheumatism with SN resulted in the recovery of deficient T cells, T-suppressors, normalization of immunoglobulin concentrations. In children with acute glomerulonephritis sodium nucleinate normalized decreased T-suppressor cells and increased IgG and circulating immune complexes (CIC), resulting in a pronounced remission of disease. The mechanism of desensitization and elimination of CIC by SN has not been explored, however, the parameters of SN-induced immunomodulation are known rather completely. It is suggested that SN brings about accumulation in the cell of cyclic AMP which diminished membrane permeability, activates monoaminooxidase resulting in the degradation of histamine and other biogenic amines, enhances the synthesis of endogenous corticosteroids with their desensitizing properties. All these effects contribute to the elimination of delayed type hypersensitivity. The role of SN in the inhibition of delayed type hypersensitivity remains obscure.     

Modes of antifungal action of alkanols against Saccharomyces cerevisiae

Primary aliphatic alcohols from C(6) to C(13) were tested for their antifungal activity against Saccharomyces cerevisiae. Undecanol was found to be the most potent fungicide followed by decanol. The time-kill curve study showed that undecanol was fungicidal against S. cerevisiae at any growth stages. This fungicidal activity was not influenced by pH values. The alcohols tested inhibited glucose-induced acidification by inhibiting the plasma membrane H(+)-ATPase. The primary antifungal action of amphipathic medium-chain (C(9)-C(12)) alkanols comes mainly from their ability as nonionic surfactants to disrupt the native membrane-associated function of the integral proteins. Hence, the antifungal activity of alkanols is mediated by biophysical process, and the maximum activity can be obtained when balance between hydrophilic and hydrophobic portions becomes the most appropriate.     

New data on the tachyphylactic properties of sodium nucleinate]

Sodium nucleinate, when injected into mice in combination with killed E. coli or prodigiozan, caused a decrease in side effects produced by the vaccine or polysaccharide. The combined injection of sodium nucleinate and prodigiozan in doses, ineffective if introduced separately, was accompanied by the potentiation of their tachyphylactic action. The use of sodium nucleinate in combination with polyvinylprrolidone (hemodez) prolonged the tachyphylactic action of sodium nucleinate and increased its effectiveness. The proposed principle is supposed to be suitable for decreasing the reactogenicity of bacterial vaccines and polysaccharides.     

A dominant interfering mutation in RAS1 of Saccharomyces cerevisiae

A mutant allele of RAS1 that dominantly interferes with the wild-type Ras function in the yeast Saccharomyces cerevisiae was discovered during screening of mutants that suppress an ira2 disruption mutation. A single amino acid substitution, serine for glycine at position 22, was found to cause the mutant phenotype. The inhibitory effect of the RAS1 ^Ser22 gene could be overcome either by overexpression of CDC25 or by the ira2 disruption mutation. These results suggest that the RAS1^Ser22 gene product interferes with the normal interaction of Ras with Cdc25 by forming a dead-end complex between Ras1^Ser22 and Cdc25 proteins.     

Estimating the per-base-pair mutation rate in the yeast Saccharomyces cerevisiae

Although mutation rates are a key determinant of the rate of evolution they are difficult to measure precisely and global mutations rates (mutations per genome per generation) are often extrapolated from the per-base-pair mutation rate assuming that mutation rate is uniform across the genome. Using budding yeast, we describe an improved method for the accurate calculation of mutation rates based on the fluctuation assay. Our analysis suggests that the per-base-pair mutation rates at two genes differ significantly (3.80x10(-10) at URA3 and 6.44x10(-10) at CAN1) and we propose a definition for the effective target size of genes (the probability that a mutation inactivates the gene) that acknowledges that the mutation rate is nonuniform across the genome.     

Antimicrobial action of palmarosa oil (Cymbopogon martinii) on Saccharomyces cerevisiae

The essential oil extracted from palmarosa (Cymbopogon martinii) has proven anti-microbial properties against cells of Saccharomyces cerevisiae. Low concentrations of the oil (0.1%) inhibited the growth of S. cerevisiae cells completely. The composition of the sample of palmarosa oil was determined as 65% geraniol and 20% geranyl acetate as confirmed by GC-FTIR. The effect of palmarosa oil in causing K(+) leakage from yeast cells was attributed mainly to geraniol. Some leakage of magnesium ions was also observed. Blocking potassium membrane channels with caesium ions before addition of palmarosa oil did not change the extent of K(+) ion leakage, which was equal to the total sequestered K(+) in the cells. Palmarosa oil led to changes in the composition of the yeast cell membrane, with more saturated and less unsaturated fatty acids in the membrane after exposure of S. cerevisiae cells to the oil. Some of the palmarosa oil was lost by volatilization during incubation of the oil with the yeast cells. The actual concentration of the oil components affecting the yeast cells could not therefore be accurately determined.