Oxidative stress in bacteria and protein damage by reactive oxygen species

The advent of O2 in the atmosphere was among the first major pollution events occurred on earth The reaction between ferrous iron, very abundant in the reductive early atmosphere, and oxygen results in the formation of harmful superoxide and hydroxyl radicals, which affect all macromolecules (DNA, lipids and proteins). Living organisms have to build up mechanisms to protect themselves against oxidative stress, with enzymes such as catalase and superoxide dismutase, small proteins like thioredoxin and glutaredoxin, and molecules such as glutathione. Bacterial genetic responses to oxidative stress are controlled by two major transcriptional regulators (OxyR and SoxRS). This paper reviews major key points in the generation of reactive oxygen species in bacteria, defense mechanisms and genetic responses to oxidative stress. Special attention is paid to the oxidative damage to proteins

Mitochondrial localization of the yeast forkhead factor Hcm1

Hcm1 is a member of the forkhead transcription factor family involved in segregation, spindle pole dynamics, and budding in Saccharomyces cerevisiae. Our group described the role of Hcm1 in mitochondrial biogenesis and stress resistance, and in the cellular adaptation to mitochondrial respiratory metabolism when nutrients decrease. Regulation of Hcm1 activity occurs at the protein level, subcellular localization, and transcriptional activity. Here we report that the amount of protein increased in the G1/S transition phase when the factor accumulated in the nucleus. In the G2/M phases, the Hcm1 amount decreased, and it was translocated outside the nucleus with a network-like localization. Preparation of highly purified mitochondria by a sucrose gradient density demonstrated that Hcm1 colocalized with mitochondrial markers, inducing expression of COX1, a mitochondrial encoded subunit of cytochrome oxidase, in the G2/M phases. Taken together, these results show a new localization of Hcm1 and suggest that it acts as a mitochondrial transcription factor regulating the metabolism of this organelle.This research was funded by Ministerio de Ciencia e Innovación (Spain), grants BFU2010-17387 and CSD2007-20 Consolider Ingenio

Reduction of oxidative cellular damage by overexpression of the thioredoxin TRX2 gene improves yield and quality of wine yeast dry active biomass

<p>Abstract</p> <p>Background</p> <p>Wine <it>Saccharomyces cerevisiae </it>strains, adapted to anaerobic must fermentations, suffer oxidative stress when they are grown under aerobic conditions for biomass propagation in the industrial process of active dry yeast production. Oxidative metabolism of sugars favors high biomass yields but also causes increased oxidation damage of cell components. The overexpression of the <it>TRX2 </it>gene, coding for a thioredoxin, enhances oxidative stress resistance in a wine yeast strain model. The thioredoxin and also the glutathione/glutaredoxin system constitute the most important defense against oxidation. Trx2p is also involved in the regulation of Yap1p-driven transcriptional response against some reactive oxygen species.</p> <p>Results</p> <p>Laboratory scale simulations of the industrial active dry biomass production process demonstrate that <it>TRX2 </it>overexpression increases the wine yeast final biomass yield and also its fermentative capacity both after the batch and fed-batch phases. Microvinifications carried out with the modified strain show a fast start phenotype derived from its enhanced fermentative capacity and also increased content of beneficial aroma compounds. The modified strain displays an increased transcriptional response of Yap1p regulated genes and other oxidative stress related genes. Activities of antioxidant enzymes like Sod1p, Sod2p and catalase are also enhanced. Consequently, diminished oxidation of lipids and proteins is observed in the modified strain, which can explain the improved performance of the thioredoxin overexpressing strain.</p> <p>Conclusions</p> <p>We report several beneficial effects of overexpressing the thioredoxin gene <it>TRX2 </it>in a wine yeast strain. We show that this strain presents an enhanced redox defense. Increased yield of biomass production process in <it>TRX2 </it>overexpressing strain can be of special interest for several industrial applications.</p