Mitochondrial ribosomal proteins involved in tellurite resistance in yeast Saccharomyces cerevisiae.

A considerable body of evidence links together mitochondrial dysfunctions, toxic action of metalloid oxyanions, and system and neurodegenerative disorders. In this study we have used the model yeast Saccharomyces cerevisiae to investigate the genetic determinants associated with tellurite resistance/sensitivity. Nitrosoguanidine-induced K2TeO3-resistant mutants were isolated, and one of these mutants, named Sc57-Te5R, was characterized. Both random spore analysis and tetrad analysis and growth of heterozygous (TeS/Te5R) diploid from Sc57-Te5R mutant revealed that nuclear and recessive mutation(s) was responsible for the resistance. To get insight into the mechanisms responsible for K2TeO3-resistance, RNA microarray analyses were performed with K2TeO3-treated and untreated Sc57-Te5R cells. A total of 372 differentially expressed loci were identified corresponding to 6.37% of the S. cerevisiae transcriptome. Of these, 288 transcripts were up-regulated upon K2TeO3 treatment. About half of up-regulated transcripts were associated with the following molecular functions: oxidoreductase activity, structural constituent of cell wall, transporter activity. Comparative whole-genome sequencing allowed us to identify nucleotide variants distinguishing Sc57-Te5R from parental strain Sc57. We detected 15 CDS-inactivating mutations, and found that 3 of them affected genes coding mitochondrial ribosomal proteins (MRPL44 and NAM9) and mitochondrial ribosomal biogenesis (GEP3) pointing out to alteration of mitochondrial ribosome as main determinant of tellurite resistance.

Sorghum, a healthy and gluten-free food for celiac patients as demonstrated by genome, biochemical, and immunochemical analyses.

Wheat (Triticum spp. L.), rye (Secale cereal L.), and barley (Hordeum vulgare L.) seeds contain peptides toxic to celiac patients. Maize (Zea mays L.) and rice (Oryza sativa L.) are distant relatives of wheat as well as sorghum (Sorghum bicolor (L.) Moench) and are known to be safe for celiacs. Both immunochemical studies and in vitro and in vivo challenge of wheat-free sorghum food products support this conclusion, although molecular evidence is missing. The goal of the present study was to provide biochemical and genetic evidence that sorghum is safe for celiac patients. In silico analysis of the recently published sorghum genome predicts that sorghum does not contain peptides that are toxic for celiac patients. Aqueous/alcohol-soluble prolamins (kafirins) from different sorghum varieties, including pure lines and hybrids, were evaluated by SDS-PAGE and HPLC analyses as well as an established enzyme-linked immunosorbent assay (ELISA) based on the R5 antibody. These analyses provide molecular evidence for the absence of toxic gliadin-like peptides in sorghum, confirming that sorghum can be definitively considered safe for consumption by people with celiac disease.

Effects of tellurite on growth of Saccharomyces cerevisiae.

The effects of potassium tellurite on growth and survival of rho(+) and rho(0) Saccharomyces cerevisiae strains were investigated. Both rho(+) and rho(0) strains grew on a fermentable carbon source with up to 1.2 mM K(2)TeO(3), while rho(+) yeast cells grown on a non-fermentable carbon source were inhibited at tellurite levels as low as 50 muM suggesting that this metalloid specifically inhibited mitochondrial functions. Growth of rho(+) yeast cells in the presence of increasing amount of tellurite resulted in dose-dependent blackening of the culture, a phenomenon not observed with rho(0) cultures. Transmission electron microscopy of S. cerevisiae rho(+) cells grown in the presence of tellurite showed that blackening was likely due to elemental tellurium (Te(0)) that formed large deposits along the cell wall and small precipitates in both the cytoplasm and mitochondria.

Nitrite metabolism in Debaryomyces hansenii TOB-Y7, a yeast strain involved in tobacco fermentation.

The Italian cigar manufacturing process includes a fermentation step that leads to accumulation of nitrite and tobacco-specific nitrosamines (TSNA), undesirable by-products due to their negative impact on health. In this study, growth and biochemical properties of Debaryomyces hansenii TOB-Y7, a yeast strain that predominates during the early phase of fermentation, have been investigated. With respect to other D. hansenii collection strains (Y7426, J26, and CBS 1796), TOB-Y7 was characterized by the ability to tolerate very high nitrite levels and to utilize nitrite, but not nitrate, as a sole nitrogen source in a chemically defined medium, a property that was enhanced in microaerophilic environment. The ability to assimilate nitrite was associated to the presence of YNI1, the gene encoding the assimilatory NAD(P)H:nitrite reductase (NiR), absent in Y7426, J26, and CBS 1796 by Southern blot data. YNI1 from TOB-Y7 was entirely sequenced, and its expression was analyzed in different media by Northern blot and reverse transcriptase polymerase chain reaction. The evidence that, in D. hansenii TOB-Y7, YNI1 was transcriptional active also in the presence of high ammonia concentration typical of tobacco fermentation, stimulated the development of an improved process that, on a laboratory scale, was proved to be effective in minimizing nitrite and TSNA accumulation.

Phenotypes of a naturally defective recB allele in Neisseria meningitidis clinical isolates.

Neisseria meningitidis strains belonging to the hypervirulent lineage ET-37 and several unrelated strains are extremely UV sensitive. The phenotype is consequent to the presence of a nonfunctional recB(ET-37) allele carrying multiple missense mutations. Phenotypic analysis has been performed with congenic meningococcal strains harboring either the wild-type recB allele or the recB(ET-37) allele. Congenic recB(ET-37) meningococci, in addition to being sensitive to UV, were defective both in repair of DNA lesions induced by UV treatment and, partially, in recombination-mediated transformation. Consistently, the wild-type, but not the recB(ET-37), allele was able to complement the Escherichia coli recB21 mutation to UV resistance and proficiency in recombination. recB(ET-37) meningococci did not exhibit higher frequencies of spontaneous mutation to rifampin resistance than recB-proficient strains. However, mutation rates were enhanced following UV treatment, a phenomenon not observed in the recB-proficient counterpart. Interestingly, the results of PCR-based assays demonstrated that the presence of the recB(ET-37) allele considerably increased the frequency of recombination at the pilin loci. The main conclusion that can be drawn is that the presence of the defective recB(ET-37) allele in N. meningitidis isolates causes an increase in genetic diversity, due to an ineffective RecBCD-dependent DNA repair and recombination pathway, and an increase in pilin antigenic variation.