Descripción: The possible associations between longevity, early fecundity, and stress-resistance traits were explored using artificial selection on longevity in a laboratory population of Drosophila buzzatii. Three replicated lines were selected for increased lifespan (L lines) and compared with the respective unselected controls (C lines) after the 14th generation of selection. Mean longevity exhibited a significant response to selection. The baseline mortality tended to decrease in the L lines and a negative correlated response to longevity selection was found for early fecundity. Egg-to-adult developmental time increased in L lines. Longevity selection increased stress resistance for both high and low temperatures, as measured by heat knockdown resistance and chill-coma recovery. Starvation resistance also tended to be higher in L than in C lines. The results obtained are consistent with the hypothesis of trade-offs between longevity and early fecundity, and also suggest a trade-off association between adult longevity and developmental time. Correlated selection responses were generally consistent with correlations among the traits previously inferred from altitudinal clines for longevity and stress-resistance phenotypes. © 2009 The Linnean Society of London.

Descripción: Phasins (PhaP) are proteins normally associated with granules of poly(3-hydroxybutyrate) (PHB), a biodegradable polymer accumulated by many bacteria as a reserve molecule. These proteins enhance growth and polymer production in natural and recombinant PHB producers. It has been shown that the production of PHB causes stress in recombinant Escherichia coli, revealed by an increase in the concentrations of several heat stress proteins. In this work, quantitative reverse transcription (qRT)-PCR analysis was used to study the effect of PHB accumulation, and that of PhaP from Azotobacter sp. strain FA8, on the expression of stress-related genes in PHB-producing E. coli. While PHB accumulation was found to increase the transcription of dnaK and ibpA, the expression of these genes and of groES, groEL, rpoH, dps, and yfiD was reduced, when PhaP was coexpressed, to levels even lower than those detected in the non-PHB-accumulating control. These results demonstrated the protective role of PhaP in PHB-synthesizing E. coli and linked the effects of the protein to the expression of stress-related genes, especially ibpA. The effect of PhaP was also analyzed in non-PHBsynthesizing strains, showing that expression of this heterologous protein has an unexpected protective effect in E. coli, under both normal and stress conditions, resulting in increased growth and higher resistance to both heat shock and superoxide stress by paraquat. In addition, PhaP expression was shown to reduce RpoH protein levels during heat shock, probably by reducing or titrating the levels of misfolded proteins. © 2011, American Society for Microbiology.

Descripción: Survival of a potentially lethal high temperature stress is a genetically variable thermal adaptation trait in many organisms. Organisms cope with heat stress by basal or induced thermoresistance. Here, we tested quantitative trait loci (QTL) for heat stress survival (HSS) in Drosophila melanogaster, with and without a cyclic heat-hardening pre-treatment, for flies that were reared at low (LD) or high (HD) density. Mapping populations were two panels of recombinant inbred lines (RIL), which were previously constructed from heat stress-selected stocks: RIL-D48 and RIL-SH2, derived from backcrosses to stocks of low and high heat resistance, respectively. HSS increased with heat hardening in both LD and HD flies. In addition, HSS increased consistently with density in non-hardened flies. There was a significant interaction between heat hardening and density effects in RIL-D48. Several QTL were significant for both density and hardening treatments. Many QTL overlapped with thermotolerance QTL identified for other traits in previous studies based on LD cultures only. However, three new QTL were found in HD only (cytological ranges: 12E-16F6; 30A3-34C2; 49C-50C). Previously found thermotolerance QTL were also significant for flies from HD cultures. © 2012. Published by The Company of Biologists Ltd.

Descripción: We have studied the effects of accumulating cyclic electrical pulses of increasing amplitude on the non-volatile resistance state of interfaces made by sputtering a metal (Au, Pt) on top of the surface of a cuprate superconductor YBa2Cu3O7-δ. We have analyzed the influence of the number of applied pulses N on the relative amplitude of the remnant resistance change between the high (RH) and the low (R L) state [( = (R H-R L) / R L] at different temperatures (T). We show that the critical voltage (Vc) needed to produce a resistive switching (RS, i.e., > 0) decreases with increasing N or T. We also find a power law relation between the voltage of the pulses and the number of pulses N 0 required to produce a RS of = 0. This relation remains very similar to the Basquin equation used to describe the stress-fatigue lifetime curves in mechanical tests. This points out to the similarity between the physics of the RS, associated with the diffusion of oxygen vacancies induced by electrical pulses, and the propagation of defects in materials subjected to repeated mechanical stress. © 2013 AIP Publishing LLC.

Descripción: Polyhydroxyalkanoates (PHAs) are accumulated as intracellular granules by many bacteria under unfavorable conditions, enhancing their fitness and stress resistance. Poly(3-hydroxybutyrate) (PHB) is the most widespread and best-known PHA. Apart from the genes that catalyze polymer biosynthesis, natural PHA producers have several genes for proteins involved in granule formation and/or with regulatory functions, such as phasins, that have been shown to affect polymer synthesis. This study evaluates the effect of PhaP, a phasin, on bacterial growth and PHB accumulation from glycerol in bioreactor cultures of recombinant Escherichia coli carrying phaBAC from Azotobacter sp. strain FA8. Cells expressing phaP grew more, and accumulated more PHB, both using glucose and using glycerol as carbon sources. When cultures were grown in a bioreactor using glycerol, PhaP-bearing cells produced more polymer (2.6 times) and more biomass (1.9 times) than did those without the phasin. The effect of this protein on growth promotion and polymer accumulation is expected to be even greater in high-density cultures, such as those used in the industrial production of the polymer. The recombinant strain presented in this work has been successfully used for the production of PHB from glycerol in bioreactor studies, allowing the production of 7.9 g/liter of the polymer in a semisynthetic medium in 48-h batch cultures. The development of bacterial strains that can efficiently use this substrate can help to make the industrial production of PHAs economically feasible. Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Descripción: To determine whether the stationary sigma factor, σS, influences polyhydroxyalkanoate metabolism in Pseudomonas putida KT2440, an rpoS-negative mutant was constructed to evaluate polyhydroxyalkanoate accumulation and expression of a translational fusion to the promoter region of the genes that code for polyhydroxyalkanoate synthase 1 (phaC1) and polyhydroxyalkanoate depolymerase (phaZ). By comparison with the wild-type, the rpoS mutant showed a higher polyhydroxyalkanoate degradation rate and increased expression of the translational fusion during the stationary growth phase. These results suggest that σS might control the genes involved in polyhydroxyalkanoate metabolism, possibly in an indirect manner. In addition, survival and oxidative stress assays performed under polyhydroxyalkanoate- and nonpolyhydroxyalkanoate- accumulating conditions demonstrated that the accumulated polyhydroxyalkanoate increased the survival and stress tolerance of the rpoS mutant. According to this, polyhydroxyalkanoate accumulation would help cells to overcome the adverse conditions encountered during the stationary phase in the strain that lacks RpoS. © 2008 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Descripción: Pseudomonas oleovorans GPo1 and its polyhydroxyalkanoic acid (PHA) depolymerization-minus mutant, GPo500 phaZ, residing in natural water microcosms, were utilized to asses the effect of PHA availability on survival and resistance to stress agents. The wild-type strain showed increased survival compared to the PHA depolymerase-minus strain. The appearance of a round cellular shape, characteristic of bacteria growing under starvation conditions, was delayed in the wild type in comparison to the mutant strain. Percent survival at the end of ethanol and heat challenges was always higher in GPo1 than in GPo500. Based on these results and on early experiments (H. Hippe, Arch. Mikrobiol. 56:248-277, 1967) that suggested an association of PHA utilization with respiration and oxidative phosphorylation, we investigated the association between PHA degradation and nucleotide accumulation. ATP and guanosine tetraphosphate (ppGpp) production was analyzed under culture conditions leading to PHA depolymerization. A rise in the ATP and ppGpp levels appeared concomitant with PHA degradation, while this phenomenon was not observed in the mutant strain unable to degrade the polymer. Complementation of the phaZ mutation restored the wild-type phenotype.

Descripción: Aims: To study the modification of the cell wall of Lactobacillus casei ATCC 393 grown in high salt conditions. Methods and Results: Differences in the overall structure of cell wall between growth in high salt (MRS + 1 mol l -1 NaCl; N condition) and control (MRS; C condition) conditions were determined by transmission electronic microscopy and analytical procedures. Lactobacillus casei cells grown in N condition were significantly larger than cells grown under unstressed C condition. Increased sensitivity to mutanolysin and antibiotics with target in the cell wall was observed in N condition. Purified cell wall also showed the increased sensitivity to lysis by mutanolysin. Analysis of peptidoglycan (PG) from stressed cells showed that modification was at the structural level in accordance with a decreased PG cross-link involving penicillin-binding proteins (PBP). Nine PBP were first described in this species and these proteins were expressed in low percentages or presented a modified pattern of saturation with penicillin G (Pen G) during growth in high salt. Three of the essential PBP were fully saturated in N condition at lower Pen G concentrations than in C condition, suggesting differences in functionality in vivo. Conclusions: The results show that growth in high salt modified the structural properties of the cell wall. Significance and Impact of Study: Advances in understanding the adaptation to high osmolarity, in particular those involving sensitivity to lysis of lactic acid bacteria.