Hydrogen peroxide induces a specific DNA base change profile in the presence of the iron chelator 2, 2’ dipyridyl in Escherichia coli

Pretreatment of Escherichia coli cultures with the iron chelator 2,2’-dipyridyl (1 mM) protects against the lethal effects of low concentrations of hydrogen peroxide (<15 mM). However, at H2O2 concentrations equal to or greater than 15 mM, dipyridyl pretreatment increases lethality and mutagenesis, which is attributed to the formation of different types of DNA lesions. We show here that pretreatment with dipyridyl (1 mM) prior to challenge with high H2O2 concentrations (≥15 mM) induced mainly G:C→A:T transitions (more than 100X with 15 mM and more than 250X with 20 mM over the spontaneous mutagenesis rate) in E. coli. In contrast, high H2O2 concentrations in the absence of dipyridyl preferentially induced A:T→T:A transversions (more than 1800X and more than 300X over spontaneous mutagenesis for 15 and 20 mM, respectively). We also show that in the fpg nth double mutant, the rpoB gene mutation (RifS-RifR) induced by 20 mM H2O2 alone (20X higher) was increased in 20 mM H2O2 and dipyridyl-treated cultures (110X higher), suggesting additional and/or different lesions in cells treated with H2O2 under iron deprivation. It is suggested that, upon iron deprivation, cytosine may be the main damaged base and the origin of the pre-mutagenic lesions induced by H2O2.

Chromosomal organization of simple sequence repeats in the Pacific oyster (Crassostrea gigas): (GGAT)(4), (GT)(7) and (TA)(10) chromosome patterns.

Chromosome identification is essential in oyster genomic research. Fluorescence in situ hybridization (FISH) offers new opportunities for the identification of oyster chromosomes. It has been used to locate satellite DNAs, telomeres or ribosomal DNA sequences. However, regarding chromosome identification, no study has been conducted with simple sequence repeats (SSRs). FISH was used to probe the physical organization of three particular SSRs, (GGAT)(4), (GT)(7) and (TA)(10) onto metaphase chromosomes of the Pacific oyster, Crassostrea gigas. Hybridization signals were observed in all the SSR probes, but the distribution and intensity of signals varied according to the oligonucleotide repeat. The intercalary, centromeric and telomeric bands were observed along the chromosomes, and for each particular repeat every chromosome pair presented a similar pattern, allowing karyotypic analysis with all the SSRs tested. Our study is the first in mollusks to show the application of SSR in situ hybridization for chromosome identification and karyotyping. This technique can be a useful tool for oyster comparative studies and to understand genome organization in different oyster taxa.

Avaliação fototóxica e screening mutagênico de extratos de propolis, Aloe spp. e Hamamelis virginiana / Evaluation of phototoxic and mutagenic activity of propolis, Aloe spp. and Hamamelis virginiana extracts

A utilização de extratos vegetais em produtos farmacêuticos e cosméticos tem mostrado ser uma tendência mundial e cresceu substancialmente nas duas últimas décadas. No entanto, há ainda poucos relatos na literatura com relação à atividade mutagênica ou fototóxica de extratos vegetais. No presente trabalho foi avaliada a atividade fototóxica e o screening mutagênico de extratos fuidos e secos de própolis, Aloe spp. e Hamamelis virginiana. Na investigação de fototoxicidade foram realizados ensaios microbiológicos, utilizando cepas de Candida albicans e Saccharomyces cerevisiae, bem como ensaios biológicos com cobaias albinos. Extratos etanólicos de Ruta graveolens e Citrus spp., além de 8-metoxipsoraleno (fármaco sintético padrão), foram usados como controles positivos de ambos os testes. A atividade mutagênica foi avaliada qualitativamente segundo o spot test descrito por Maron & Ames, com cepas de Salmonella typhimurium TA97, TA98, TA100 e TA102, empregando como controle positivo o óxido de 4-nitroquinolina. Não foi observada atividade fototóxica, em ambos os ensaios realizados, para qualquer dos extratos. O ensaio microbiológico demonstrou uma atividade fungistática ou fungicida nos extratos secos de hamamélis. Os resultados obtidos nos ensaios microbiológicos com a levedura S. cerevisiae indicam que este microrganismo apresentou eficiência no procedimento de screening de atividade fototóxica comparável à obtida com C. albicans. Os extratos vegetais não apresentaram atividade mutagênica nos ensaios preliminares realizados

Análise epidemiológica de consenso nacional sobre espasticidade / Epidemiological analysis of nacional consense about spasticity

The National Consense abot Spasticity by Brazilian Society of Physical Medicine and Rehabilitation (SBMFR) and Brazilian Medical Association (AMB) was done based on critical analysis of epidemiological studies, showing that traditional terapeutic resources need more studies for posterior approving

Lethal interaction between hydrogen peroxide and o-phenanthroline in Escherichia coli

The iron chelator o-phenanthroline enhances the lethal effect of H2O2 about four hundred times in Escherichia coli when both substances are added simultaneously to the culture mediu. If o-phenanthroline is added for increasing periods of time prior to the addition of H2O2, there is a shift from this lethal interaction to protection by the chelator about seven hundred times. It is known that the Fe2+ -o-phenanthroline(I) and Fe2+ -o-phenanthroline(II) complexes are formed quickly whereas the final and more stable Fe2+ -o-phenanthroline(III) complex is formed slowly, Moreover, the mono and bis complexes react with H2O2 to produce OH., whereas the tris complex is stable towards H2O2. Therefore, the lethal effect could be explained by the kinetics of reaction of o-phenanthroline with intracellular Fe2+, i.e., the mono and bis complexes are more reactive than intracellular Fe2+

Membrane permeability and sensitivity to lethal heat are affected by lexA and recA mutations in Escherichia coli K12

Membrane permeability was evaluated in several SOS-deficient strains. Great heat sensitivity was observed in all the lexA (Ind-) strains, which was associated to an increase in membrane permeability (up to 120 per cent increase above the wild-type control), as assayed by the crystal violet (CV) growth inhibition. After irradiation with a single UV dose (75 J.m-2 delivered to wild-type and 2 J.m-2 to the lex A3 strain), survival was followed by plating cells in both nutrient and membrane permeability-selective (nutrient + CV) media and a great lethality due to CV was observed in a lexA mutant, which appeared to be about 100 times more sensitive to CV compared to its wild-type parent stain. The decreased membrane integrity found in the lex A-deficient strains suggests that LexA protein and/or LexA-repressed genes may interact with the bacterial membrane, which could be the location of SOS events

Mutagenic and genotoxic effects of mate (Ilex paraguariensis) in prokaryotic organisms

1. The mutagenic and genotoxic effects of mate (Ilex paraguariensis) aqueous solutions were analyzed in bacterial cells. 2. Mate solutions showed mutagenic activity in the Ames test (TA97, TA98, TA100 and TA102 strains) at concentrations of 20 to 50 mg/plate (mutagenic factors of 3.5 to 5.6) and genotoxic activity in the inductest (WP2s (lambda) strain), with a maximal phage induction at concentrations of 10 to 20 mg/plate. Above these concentrations the mate solutions were cytotoxic. 3. Addition of 5 U/ml catalase, 20 microliters/ml S9 rat liver microsomal fraction, 100 mM thiourea or 10 mM dipyridyl completely inhibited the lysogenic induction produced by mate; however, the addition of 1,000 U/ml superoxide dismutase was almost ineffective. 4. Oxygen reactive species may be present in mate solutions playing an essential role in its genotoxicity.

Chloramphenicol pretreatment enhances resistance to UV, X-rays and H2O2 damage in Escherichia coli but not of infecting UV damaged phages

Chloramphenicol pretreatment of Escherichcia coli increases resistence to UV, X-rays and H2O2 damage. Increased ssurvival of UV-irradiated, infecting gama phages is not observed. The hypothesis that enhanced survival of chloramphenicol-pretrated cells is due to the induction of plasmid "repairons" is questioned