Antimutagenic activity of vitamin B1 against damages induced by chemical and physical mutagens in Salmonella typhimurium and Escherichia coli.

Thiamine (vitamin B1) is an essential nutrient acting mainly as an enzymatic cofactor on diverse cell processes. It has been reported that vitamin B1 has a significant role in the signaling pathways related to the response to adverse environmental conditions (chemical and physical). The objectives of this study were to evaluate the antimutagenic potential of vitamin B1 in front of DNA-alkylating agents in the presence/absence of ogt and ada repairing genes in Salmonella typhimurium strains and against damage induced by ultraviolet light type C in Escherichia coli strains mutated at the uvrABC system and recBCD enzymes. For S. typhimurium, an antimutagenesis test (Ames test) was performed using strains deficient in one or both genes (YG7100 ada-/ogt+, YG7104 ada+/ogt-, YG7108 ada-/ogt-). For E. coli, mutated strains (K-12 derived strains Hfr H180 uvrB+/recA+, W3110 uvrB+/recA- and ATCC®8739 uvrB-/recA+) were exposed to UV-C light at different time intervals, with and without vitamin B1. Our results showed that thiamine is an antimutagen against methyl-N-nitro-N-nitrosoguanidine or ethyl-N-nitro-N-nitrosoguanidine only when the ogt gene is present. While for E. coli, the presence of vitamin B1 increased the survival rate, implying an antimutagenesis independent of uvrABC repairing system and recBCD enzymes.

Psoralen-sensitive mutant pso9-1 of Saccharomyces cerevisiae contains a mutant allele of the DNA damage checkpoint gene MEC3.

Complementation analysis of the pso9-1 yeast mutant strain sensitive to photoactivated mono- and bifunctional psoralens, UV-light 254 nm, and nitrosoguanidine, with pso1 to pso8 mutants, confirmed that it contains a novel pso mutation. Molecular cloning via the reverse genetics complementation approach using a yeast genomic library suggested pso9-1 to be a mutant allele of the DNA damage checkpoint control gene MEC3. Non-complementation of several sensitivity phenotypes in pso9-1/mec3Delta diploids confirmed allelism. The pso9-1 mutant allele contains a -1 frameshift mutation (deletion of one A) at nucleotide position 802 (802delA), resulting in nine different amino acid residues from that point and a premature termination. This mutation affected the binding properties of Pso9-1p, abolishing its interactions with both Rad17p and Ddc1p. Further interaction assays employing mec3 constructions lacking the last 25 and 75 amino acid carboxyl termini were also not able to maintain stable interactions. Moreover, the pso9-1 mutant strain could no longer sense DNA damage since it continued in the cell cycle after 8-MOP + UVA treatment. Taken together, these observations allowed us to propose a model for checkpoint activation generated by photo-induced adducts.

Repressor mutant forms of the Azospirillum brasilense NtrC protein.

The Azospirillum brasilense mutant strains FP8 and FP9, after treatment with nitrosoguanidine, showed a null Nif phenotype and were unable to use nitrate as their sole nitrogen source. Sequencing of the ntrC genes revealed single nucleotide mutations in the NtrC nucleotide-binding site. The phenotypes of these strains are discussed in relation to their genotypes.

Characterization and mapping of an informational suppressor in Aspergillus nidulans.

The present work was undertaken to characterize a suppressor gene present in a mutant strain of A. nidulans obtained with NTG (N-Methyl-N'-Nitro-N-Nitrosoguanidine). Analyses of this mutant have shown that this suppressor, designated suO1, induces phenotypic co-reversion of several auxotrophic mutations and makes the strain sensitive to aminoglycoside antibiotics and lower temperatures. suO1 has shown to be on linkage group VIII. The vegetative growth of the mutant strain is very unstable because the suppressor gene induces the production of prototrophic mitotic sectors. The strains bearing the suO1 gene produce cleistothecia containing a reduced number of viable ascospores during the sexual cycle. The segregation of the genetic markers has also been observed in the mutant strain self crossed. From the above results it may be concluded that suO1 is an informational suppressor.

Characterization and mapping of an informational suppressor in Aspergillus nidulans

The present work was undertaken to characterize a suppressor gene present in a mutant strain of A. nidulans obtained with NTG (N-Methyl-N'-Nitro-N-Nitrosoguanidine). Analyses of this mutant have shown that this suppressor, designated suO1, induces phenotypic co-reversion of several auxotrophic mutations and makes the strain sensitive to aminoglycoside antibiotics and lower temperatures. suO1 has shown to be on linkage group VIII. The vegetative growth of the mutant strain is very unstable because the suppressor gene induces the production of prototrophic mitotic sectors. The strains bearing the suO1 gene produce cleistothecia containing a reduced number of viable ascospores during the sexual cycle. The segregation of the genetic markers has also been observed in the mutant strain self crossed. From the above results it may be concluded that suO1 is an informational suppressor.

Zearalenone production in fusarium graminearum variants after treatment with nitrosoguanidine

A Zearalenona é um metabólito secundário produzido por Fusarium graminearum e, aparentemente, envolvido no controle de sua reproduçäo sexuada. Em alguns animais, quando ingerida, provoca efeitos estrogênicos. A reduçäo química da Zearalenona produz o derivado zearalenol, que possui efeito anabolizante em bois e ovelhas, predominando sobre o efeito estrogênico. A partir de um isolado de Fusarium graminearum, considerado bom produtor de zearalenona, investigou-se, através da açäo do mutagênico nitrosoquanidina sobre seus conidios, a possibilidade de obtençäo de variantes com maior produçäo de zearalenona. Foram selecionadas 40 amostras em funçäo de seus aspectos morfológicos, pigmentaçäo e tempo de crescimento compatíveis com exemplares mais produtores de zearalenona em isolamento natural. Através de quantificaçäo de zearalenona em HPLC, obtiveram-se 10 variantes com produçäo entre 2 a 16 vezes supeiror ao controle quando do seu isolamento. A estabilidade destes variantes foi testada através de 12 transferências sucessivas em meio de cultivo. Nas condiçöes testadas obtiveram-se 2 variantes considerados estáveis e que mantiveram a superproduçäo de zearalenona

[Biomass production enriched in intracellular methionine by a mutant of Saccharomyces cerevisiae]. / Producción de biomasa enriquecida en metionina intracelular por un mutante de Saccharomyces cerevisiae.

According with FAO reported data the methionine intracellular content in Saccharomyces cerevisiae is higher than another yeast. For increasing the yeast methionine internal concentration three S. cerevisiae mutant strains were chosen (M2, M4 y M9), obtained by ethionine (0.1 mg/ml) and norleucine (0.33 mg/ml) resistance by González Miliani (personal communication). The resistance levels in culture were modified until selection of a mutant LF-M9 etr norr, which shows resistance to ethionine (6 mg/ml). Optimal conditions for growth were fixed on shaked flasks and later mutationaly experiments were conducted with nitrosoguanidine (0.5 mg/ml) and U.V. light (240 nm in 9 minutes d = 32 cm). Mutants obtained were selected on plate replicates and microbiological test, using Escherichia coli 303 (Wollman, met- b1- strr) as the indicating strain. The mutant LF-M9 treo- etr norr, shows an intracellular methionine content 3 times higher than the control strain DSM D273-10B and 1.8 times higher than parental strain M9. The mutant was cultivated on different agroindustrial wastes and the optimal growth was reached in acid hydrolysates of cassava foliage. Fermentations in 1 litre stirred fermentor were accomplished using these medium and the biomass obtained was 6.3 g of the yeast (dry weight) enriched in methionine per litre of extract.

Genetic analysis of compact mutants of Aspergillus nidulans.

Foram isolados doze mutantes compactos de Aspergillus nidulans que apresentaram alem do reduzido crescimento, escassa producao de conidios, enrugamento da colonia em graus variaveis e alteracoes na coloracao do micelio. Eles foram obtidos a partir de linhagens normais apos tratamento com luz ultra violeta ou nitrosoguanidina. A analise genetica efetuada mostrou que sete dos mutantes apresentaram segrecao normal (1:1), enquanto que os demais mutantes apresentaram segrecao complexa indicando a ocorrencia de aberracoes cromossomicas envolvendo um ou dois grupos de ligacao. Os determinantes morfologicos foram localizados em quase todos os grupos de ligacao conhecidos, exceto para o III e VI. O consumo de oxigenio medido atraves do respirometro de Warburg foi menor nos mutantes compactos variando de 26 a 86% em relacao a linhagem normal