Implementing intelligent cores using processor virtualization for fault tolerance

Processor virtualization for process migration in distributed parallel computing systems has formed a significant component of research on load balancing. In contrast, the potential of processor virtualization for fault tolerance has been addressed minimally. The work reported in this paper is motivated towards extending concepts of processor virtualization towards ‘intelligent cores’ as a means to achieve fault tolerance in distributed parallel computing systems. Intelligent cores are an abstraction of the hardware processing cores, with the incorporation of cognitive capabilities, on which parallel tasks can be executed and migrated. When a processing core executing a task is predicted to fail the task being executed is proactively transferred onto another core. A parallel reduction algorithm incorporating concepts of intelligent cores is implemented on a computer cluster using Adaptive MPI and Charm ++. Preliminary results confirm the feasibility of the approach.

Intelligent agents for fault tolerance: from multi-agent simulation to cluster-based implementation

Recent research in multi-agent systems incorporate fault tolerance concepts, but does not explore the extension and implementation of such ideas for large scale parallel computing systems. The work reported in this paper investigates a swarm array computing approach, namely 'Intelligent Agents'. A task to be executed on a parallel computing system is decomposed to sub-tasks and mapped onto agents that traverse an abstracted hardware layer. The agents intercommunicate across processors to share information during the event of a predicted core/processor failure and for successfully completing the task. The feasibility of the approach is validated by simulations on an FPGA using a multi-agent simulator, and implementation of a parallel reduction algorithm on a computer cluster using the Message Passing Interface.

Physiological and proteomic approaches to address heat tolerance during anthesis in rice (Oryza sativa L.)

Episodes of high temperature at anthesis, which in rice is the most sensitive stage to temperature, are expected to occur more frequently in future climates. The morphology of the reproductive organs and pollen number, and changes in anther protein expression, were studied in response to high temperature at anthesis in three rice (Oryza sativa L.) genotypes. Plants were exposed to 6 h of high (38 °C) and control (29 °C) temperature at anthesis and spikelets collected for morphological and proteomic analysis. Moroberekan was the most heat-sensitive genotype (18% spikelet fertility at 38 °C), while IR64 (48%) and N22 (71%) were moderately and highly heat tolerant, respectively. There were significant differences among the genotypes in anther length and width, apical and basal pore lengths, apical pore area, and stigma and pistil length. Temperature also affected some of these traits, increasing anther pore size and reducing stigma length. Nonetheless, variation in the number of pollen on the stigma could not be related to measured morphological traits. Variation in spikelet fertility was highly correlated (r=0.97, n=6) with the proportion of spikelets with ≥20 germinated pollen grains on the stigma. A 2D-gel electrophoresis showed 46 protein spots changing in abundance, of which 13 differentially expressed protein spots were analysed by MS/MALDI-TOF. A cold and a heat shock protein were found significantly up-regulated in N22, and this may have contributed to the greater heat tolerance of N22. The role of differentially expressed proteins and morphology during anther dehiscence and pollination in shaping heat tolerance and susceptibility is discussed.

Varietal effects of cowpea, Vigna unguiculata, on tolerance to malathion in Callosobruchus maculatus (Coleoptera: Bruchidae)

The impact of cowpea variety on the response of cowpea bruchid, Callosobruchus maculatus, to malathion was investigated. The interaction of six cowpea varieties (Adamawa Brown, Ife BPC, Ife Brown, Lilongwe, Ntcheu and NCRI-L25) with the geographical strains of C. maculatus (Brazil and Cameroon), temperature (23, 25, 27 C) and insecticide concentration were considered. Cowpea variety (V) had an unpredictable effect on C. maculatus response to malathion. Bruchid populations produced by Ife BPC were the most susceptible to malathion while those yielded by NCRI-L25 were the most tolerant. Regardless of the cowpea variety, the Brazil strain showed higher tolerance than the Cameroon strain. There was significant effect of temperature (T) and insecticide concentration (C) on malathion tolerance in both strains (S). Likewise, there was significant impact of all two-way interactions on cowpea bruchid tolerance except V x C. Significant three-way interactions on C. maculatus tolerance to malathion was only observed in S T V and S T C. The predictability of changing one of the factors on the susceptibility of C. maculatus to insecticide was very low. This study suggests a need to take the insecticide tolerance of insect populations produced by novel varieties into account during plant breeding in addition to factors such as yield and resistance to insect and disease attack.

Synergistic effects of geographical strain, temperature and larval food on insecticide tolerance in Callosobruchus maculatus (F.)

This study investigated the multifactorial interaction of various environmental factors including 17 geographical strain (Brazil, Cameroon and Yemen strains), temperature, dose and larval food 18 (cowpea and mungbean) on the response of Callosobruchus maculatus adult to insecticide. All 19 the main factors, their two-way interactions and the four-way interaction had significant effects 20 on C. maculatus response to malathion (an organophosphate insecticide). However, the three-21 way interactions were not statistically significant (except strain x food x dose, P = 0.002). The 22 2 Brazil strain was the most responsive to temperature irrespective of the larval food type. The 23 impact of food type differs from one strain to the other, for instance, the food that imparts higher 24 tolerance in a strain might reduce the tolerance in another. Likewise, the hierarchy of tolerance 25 among the cowpea-reared strains (Brazil > Cameroon > Yemen) was totally different from the 26 mungbean-reared strains (Cameroon > Yemen > Brazil). The reasons for these differences were 27 discussed in the light of their impact on C. maculatus management. The management of both C. 28 maculatus and development of resistance could be complex, hence, the states of a variety of 29 environmental factors need to be considered. This is necessary in order to maximize management 30 success of this bruchid especially in tropical/subtropical developing countries.

Identification of components of the Sigma B Regulon in Listeria monocytogenes that contribute to acid and salt tolerance

Sigma B (σB) is an alternative sigma factor that controls the transcriptional response to stress in Listeria monocytogenes and is also known to play a role in the virulence of this human pathogen. In the present study we investigated the impact of a sigB deletion on the proteome of L. monocytogenes grown in a chemically defined medium both in the presence and in the absence of osmotic stress (0.5 M NaCl). Two new phenotypes associated with the sigB deletion were identified using this medium. (i) Unexpectedly, the strain with the ΔsigB deletion was found to grow faster than the parent strain in the growth medium, but only when 0.5 M NaCl was present. This phenomenon was independent of the carbon source provided in the medium. (ii) The ΔsigB mutant was found to have unusual Gram staining properties compared to the parent, suggesting that σB contributes to the maintenance of an intact cell wall. A proteomic analysis was performed by two-dimensional gel electrophoresis, using cells growing in the exponential and stationary phases. Overall, 11 proteins were found to be differentially expressed in the wild type and the ΔsigB mutant; 10 of these proteins were expressed at lower levels in the mutant, and 1 was overexpressed in the mutant. All 11 proteins were identified by tandem mass spectrometry, and putative functions were assigned based on homology to proteins from other bacteria. Five proteins had putative functions related to carbon utilization (Lmo0539, Lmo0783, Lmo0913, Lmo1830, and Lmo2696), while three proteins were similar to proteins whose functions are unknown but that are known to be stress inducible (Lmo0796, Lmo2391, and Lmo2748). To gain further insight into the role of σB in L. monocytogenes, we deleted the genes encoding four of the proteins, lmo0796, lmo0913, lmo2391, and lmo2748. Phenotypic characterization of the mutants revealed that Lmo2748 plays a role in osmotolerance, while Lmo0796, Lmo0913, and Lmo2391 were all implicated in acid stress tolerance to various degrees. Invasion assays performed with Caco-2 cells indicated that none of the four genes was required for mammalian cell invasion. Microscopic analysis suggested that loss of Lmo2748 might contribute to the cell wall defect observed in the ΔsigB mutant. Overall, this study highlighted two new phenotypes associated with the loss of σB. It also demonstrated clear roles for σB in both osmotic and low-pH stress tolerance and identified specific components of the σB regulon that contribute to the responses observed.

Thiamine plays a critical role in the acid tolerance of Listeria monocytogenes

Understanding the molecular basis of acid tolerance in the food-borne pathogen Listeria monocytogenes is important as this property contributes to survival in the food-chain and enhances survival within infected hosts. The aim of this study was to identify genes contributing to acid tolerance in L. monocytogenes using transposon mutagenesis and subsequently to elucidate the physiological role of these genes in acid tolerance. One mutant harboring a Tn917 insertion in the thiT gene (formerly lmo1429), which encodes a thiamine (vitamin B1) uptake system, was found to be highly sensitive to acid. The acid-sensitive phenotype associated with loss of this gene was confirmed with an independently isolated mutant, from which the thiT gene was deleted (ΔthiT). Cells of both wild-type and ΔthiT mutant that were thiamine depleted were found to be significantly more acid sensitive than control cultures. Thiamine-depleted cultures failed to produce significant concentrations of acetoin, consistent with the known thiamine dependence of acetolactate synthase, an enzyme required for acetoin synthesis from pyruvate. As acetoin synthesis is a proton-consuming process, we suggest that the acid sensitivity observed in thiamine-depleted cultures may be owing to an inability to produce acetoin.

Flooding tolerance in four 'Garrigue' landscape plants: implications for their future use in the urban landscapes of north-west Europe?

Within a changing climate, Mediterranean ‘Garrigue’ xerophytes are increasingly recommended as suitable urban landscape plants in north-west Europe, based on their capacity to tolerate high temperature and reduced water availability during summer. Such species, however, have a poor reputation for tolerating waterlogged soils; paradoxically a phenomenon that may also increase in north-west Europe due to predictions for both higher volumes of winter precipitation, and short, but intensive periods of summer rainfall. This study investigated flooding tolerance in four landscape ‘Garrigue’ species, Stachys byzantina, Cistus × hybridus, Lavandula angustifolia and Salvia officinalis. Despite evolving in a dry habitat, the four species tested proved remarkably resilient to flooding. All species survived 17 days flooding in winter, with Stachys and Lavandula also surviving equivalent flooding duration during summer. Photosynthesis and biomass production, however, were strongly inhibited by flooding although the most tolerant species, Stachys quickly restored its photosynthetic capacity on termination of flooding. Overall, survival rates were comparable to previous studies on other terrestrial (including wetland) species. Subsequent experiments using Salvia (a species we identified as ‘intermediate’ in tolerance) clearly demonstrated adaptations to waterlogging, e.g. acclimation against anoxia when pre-treated with hypoxia. Despite anecdotal information to the contrary, we found no evidence to suggest that these xerophytic species are particularly intolerant of waterlogging. Other climatic and biotic factors may restrict the viability and distribution of these species within the urban conurbations of north-west Europe, but we believe increased incidence of flooding per se should not preclude their consideration.

Characterization of a Listeria monocytogenes Scott A isolate with high tolerance towards high hydrostatic pressure

An isolate of L. monocytogenes Scott A that is tolerant to high hydrostatic pressure (HHP), named AK01, was isolated upon a single pressurization treatment of 400 MPa for 20 min and was further characterized. The survival of exponential- and stationary-phase cells of AK01 in ACES [N-(2-acetamido)-2-aminoethanesulfonic acid] buffer was at least 2 log units higher than that of the wild type over a broad range of pressures (150 to 500 MPa), while both strains showed higher HHP tolerance (piezotolerance) in the stationary than in the exponential phase of growth. In semiskim milk, exponential-phase cells of both strains showed lower reductions upon pressurization than in buffer, but again, AK01 was more piezotolerant than the wild type. The piezotolerance of AK01 was retained for at least 40 generations in rich medium, suggesting a stable phenotype. Interestingly, cells of AK01 lacked flagella, were elongated, and showed slightly lower maximum specific growth rates than the wild type at 8, 22, and 30°C. Moreover, the piezotolerant strain AK01 showed increased resistance to heat, acid, and H2O2 compared with the wild type. The difference in HHP tolerance between the piezotolerant strain and the wild-type strain could not be attributed to differences in membrane fluidity, since strain AK01 and the wild type had identical in situ lipid melting curves as determined by Fourier transform infrared spectroscopy. The demonstrated occurrence of a piezotolerant isolate of L. monocytogenes underscores the need to further investigate the mechanisms underlying HHP resistance of food-borne microorganisms, which in turn will contribute to the appropriate design of safe, accurate, and feasible HHP treatments.

Assessment of wheat cultivars for drought tolerance via osmotic stress imposed at early seedling growth stages

A study was conducted in the Department of Plant Breeding and Genetics,Sindh Agriculture University, Tandojam, Pakistan during the year 2009. Sixteen spring wheat cultivars (Triticum aestivum L.) were screened under osmotic stress with three treatments i.e. control-no PEG (polyethylene glycol), 15 percent and 25 percent PEG-6000 solution. The analysis of variance indicated significant differences among treatments for all seedling traits except seed germination percentage. Varieties also differed significantly in germination percentage, coleoptile length, shoot root length, shoot weight, root/shoot ratio and seed vigour index. However, shoot and root weights were non-significant. Significant interactions revealed that cultivars responded variably to osmotic stress treatments; hence provided better opportunity to select drought tolerant cultivars at seedling growth stages. The relative decrease over averages due to osmotic stress was 0.8 percent in seed germination, 53 percent in coleoptile length 62.9 percent in shoot length, 74.4 percent in root length, 50.6 percent in shoot weight, 45.1 percent in root weight, 30.2 percent in root/shoot ratio and 68.5 percent in seed vigour index. However, relative decrease of individual variety for various seedling traits could be more meaningful which indicated that cultivar TD-1 showed no reduction in coleoptile length, while minimum decline was noted in Anmol. For shoot length, cultivar Sarsabz expressed minimum reduction followed by Anmol. However, cultivars Anmol, Moomal, Inqalab-91, and Pavan gave almost equally lower reductions for root length suggesting their higher stress tolerance. In other words, cultivars Anmol, Moomal, Inqalab-91, Sarsabz, TD-1, ZA-77 and Pavan had relatively longer coleoptiles, shoots and roots, and were regarded as drought tolerant. Correlation coefficients among seedlings traits were significant and positive for all traits except germination percentage which had no significant correlation with any of other trait. The results indicated that increase in one trait may cause simultaneous increase in other traits; hence selection for any of these seedling attributes will lead to develop drought tolerant wheat cultivars.

Virulence in the chick model and stress tolerance of Salmonella enterica serovar Orion var. 15+

Three Salmonella enterica serovar Orion var. 15+ isolates of distinct provenance were tested for survival in various stress assays. All were less able to survive desiccation than a virulent S. Enreritidis strain, with levels of survival similar to a rpoS mutant of the S. Enteritidis strain, whereas one isolate (F3720) was significantly more acid tolerant. The S. Orion var. 15+ isolates were motile by flagellae and elaborated type-1 and curli-like fimbriae; surface organelles that are considered virulence determinants in Salmonella pathogenesis. Each adhered and invaded HEp-2 tissue culture cells with similar proficiency to the S. Enteritidis control but were significantly less virulent than S. En teritidis in the one-day-old and seven-day-old chick model. Given an oral dose of 1 x 10(3) cfu to one-day-old chicken, S. Orion var. 15+ isolates colonised 25% of liver and spleens examined at 24 h whereas S. Enteritidis colonised 100% of organs by the same with the same dose. Given an oral dose of 1 x 10(7) cfu at seven-day old, S. Orion var. 15+ failed to colonise livers and spleens in any bird examined at 24 h whereas S. Enteritidis colonised 50% of organs by the same with the same dose. Based on the number of internal organs colonised, one of the three S. Orion var. 15+ isolates tested (strain F3720) was significantly more invasive than the other two (B1 and B7). Also, strain F3720 was shed less than either B1 or B7 supporting the concept that there may be an inverse relationship between the ability to colonise deep tissues and to persist in the gut. These data are discussed in the light that S. Orion var. 15+ is associated with sporadic outbreaks of human infection rather than epidemics.