The antioxidant defence of Dekkera bruxellensis against hydrogen peroxide and its relationship to nitrate metabolism.

AIMS: The yeast Dekkera bruxellensis is a Crabtree-positive yeast that tends towards the oxidative/respiratory metabolism in aerobiosis. However, it is more sensitive to H2O2 than Saccharomyces cerevisiae. In order to investigate this metabolic paradox, the present work aimed to uncover the biological defence mechanism used by this yeast to tolerate the presence of exogenous H2O2. METHODS AND RESULTS: Growth curves and spot tests were performed to establish the values of minimal inhibitory concentration and minimal biocidal concentration of H2O2 for different combinations of carbon and nitrogen sources. Cells in exponential growth phase in different culture conditions were used to measure superoxide and thiols [protein (PT) and non-PT], enzyme activities and gene expression. CONCLUSIONS: The combination of glutathione peroxidase (Gpx) and sulfhydryl-containing PT formed the preferred defence mechanism against H2O2, which was more efficiently active under respiratory metabolism. However, the action of this mechanism was suppressed when the cells were metabolizing nitrate (NO3). SIGNIFICANCE AND IMPACT OF STUDY: These results were relevant to figure out the fitness of D. bruxellensis to metabolize industrial substrates containing oxidant molecules, such as molasses and plant hydrolysates, in the presence of a cheaper nitrogen source such as NO3.

Vitamin D receptor polymorphisms and expression profile in rheumatoid arthritis Brazilian patients.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation and important joint commitment, being the most common systemic autoimmune disease worldwide. RA displays important genetic background with a variety of genes contributing to the immune balance breakdown. Recent studies have demonstrated that vitamin D, through its receptor (VDR), is able to regulate the immune balance and suppress the autoimmunity process, being a potential target in autoimmune diseases. In the present genetic association study, we assessed 5 Tag single nucleotide polymorphisms (SNPs) (rs11168268, rs2248098, rs1540339, rs4760648 and rs3890733), which cover most of the VDR gene, in three different Brazilian populations (from Northeast, Southeast and South Brazil). We also evaluated the VDR expression profile in whole blood and monocytes from RA patients. For genotyping study, 428 RA patients and 616 healthy controls were genotyped with fluorogenic allele specific probes on an ABI7500 platform. For gene expression study, VDR mRNA levels of 15 RA patients and 26 healthy individuals were assessed by RT-PCR. Our results showed that SNPs rs4760648 and rs3890733 are associated to RA susceptibility (p value = 0.0026, OR 1.31 and p value = 0.0091, OR 1.28 with statistical power = 0.999 and 0.993, respectively). Regarding RA clinical features, the studied SNPs did not show significant associations. The gene expression assays showed that VDR mRNA levels were down regulated in both whole blood (-3.3 fold) and monocytes (-3.2 fold) of RA patients when compared to healthy controls. Our results, the first reported for distinct Brazilian populations, support a role of the VDR gene in the susceptibility to RA.

5-Hydroxymethylfurfural induces ADH7 and ARI1 expression in tolerant industrial Saccharomyces cerevisiae strain P6H9 during bioethanol production.

The aims of this work were to obtain, by evolutionary engineering, an industrial strain of Saccharomyces cerevisiae tolerant to high concentrations of HMF and to determine the expression levels of genes previously described as responsible for this tolerance. Cells were grown under anaerobic and oxygen limited conditions, in the presence of glucose or sucrose as carbon sources. P6H9 strain presented high expression levels for genes ADH7 and ARI1 in presence of HMF. This tolerant strain also showed higher ethanol productivity, biomass formation and alcohol dehydrogenase activity comparing to sensitive strains. Results suggest that S. cerevisiae P6H9 strain presents potential to be used for second-generation ethanol production.

Quantitative aerobic physiology of the yeast Dekkera bruxellensis, a major contaminant in bioethanol production plants.

Dekkera bruxellensis has been described as the major contaminant yeast of industrial ethanol production, although little is known about its physiology. The aim of this study was to investigate the growth of this yeast in diverse carbon sources and involved conducting shake-flask and glucose- or sucrose-limited chemostats experiments, and from the chemostat data, the stoichiometry of biomass formation during aerobic growth was established. As a result of the shake-flask experiments with hexoses or disaccharides, the specific growth rates were calculated, and a different behavior in rich and mineral medium was observed concerning to profile of acetate and ethanol production. In C-limited chemostats conditions, the metabolism of this yeast was completely respiratory, and the biomass yields reached values of 0.62 gDW gS(-1) . In addition, glucose pulses were applied to the glucose- or sucrose-limited chemostats. These results showed that D. bruxellensis has a short-term Crabtree effect. While the glucose pulse was at the sucrose-limited chemostat, sucrose accumulated at the reactor, indicating the presence of a glucose repression mechanism in D. bruxellensis.