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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has been shown previously that the otsA and otsB mutations block osmoregulatory trehalose synthesis in Escherichia coli. We report that the transcription of these osmoregulated ots genes is dependent on KatF (AppR), a putative sigma factor for certain stationary phase- and starvation-induced genes. The transcription of the osmoregulated bet and proU genes was not katF dependent. Our genetic analysis showed that katF carries an amber mutation in E. coli K-12 and many of its derivatives but that katF has reverted to an active form in the much-used strain MC4100. This amber mutation in katF leads to strain variations in trehalose synthesis and other katF-dependent functions of E. coli. We have performed a molecular cloning of the otsBA genes, and we present evidence that they constitute an operon encoding trehalose-6-phosphate phosphatase and trehalose-6-phosphate synthase. A cloning and restriction site analysis, performed by comparing the cloned fragments with the known physical map of the E. coli chromosome, revealed that the otsBA genes are situated on a 2.9-kb HindIII fragment located 8 to 11 kb clockwise of tar (41.6 min).
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PMID:Molecular cloning and physical mapping of the otsBA genes, which encode the osmoregulatory trehalose pathway of Escherichia coli: evidence that transcription is activated by katF (AppR) 131 94

The polymorphic life history of the marine naked amoeba Flabellula baltica was studied. It can be interpreted in terms of adaptations to an environment that is patchy in time and space and it represents trade-off between longevity during starvation and the ability to initiate multiplication soon after food resource become available. The life history also represents bet hedging in that different cells within a clonal culture may respond in different ways when food is depleted.
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PMID:The life history of Flabellula baltica Smirnov (Gymnamoebae, Rhizopoda): adaptations to a spatially and temporally heterogeneous environment. 2001 61

The majority of phytophagous insects are relatively specialized in their food habits, and specialization in resource use is expected to be favored by selection in most scenarios. Ecological generalization is less common and less well understood, but it should be selected for by (1) rarity of resources, (2) resource inconstancy, or (3) unreliability of resource quality. Here, we test these predictions by studying egg distribution and offspring survival in the orange tip butterfly, Anthocharis cardamines, on different host plants in Sweden over a five-year period. A total of 3800 eggs were laid on 16 of the 18 crucifers available at the field site during the five years. Three main factors explained host plant generalization: (1) a rarity of food resources in which the female encounter rate of individual crucifer plants was low and within-year phenological succession of flowering periods of the different crucifers meant that individual species were suitable for oviposition only within a short time window, which translates to a low effective abundance of individual crucifer species as experienced by females searching for host plants, making specialization on a single crucifer species unprofitable; (2) variation in food resources in which among-year variation in availability of any one host plant species was high; and (3) larval survivorship varied unpredictably among years on all host plants, thereby necessitating a bet-hedging strategy and use of several different host plants. Unpredictable larval survival was caused by variation in plant stand habitat characteristics, which meant that drowning and death from starvation affected different crucifers differently, and by parasitism, which varied by host plant and year. Hence, our findings are in agreement with the theoretical explanation of ecological generalization above, helping to explain why A. cardamines is a generalist throughout its range with respect to genera within the Cruciferae.
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PMID:The evolutionary ecology of generalization: among-year variation in host plant use and offspring survival in a butterfly. 2012 Aug 9

The expression of phenotypic variability can enhance geometric mean fitness and act as a bet-hedging strategy in unpredictable environments. Metazoan bet hedging usually involves phenotypic diversification among an individual's offspring, such as differences in seed dormancy. Virtually all known microbial bet-hedging strategies, in contrast, rely on low-probability stochastic switching of a heritable phenotype by individual cells in a clonal group. This is less effective at generating within-group diversity when group size is small. Here we describe a novel microbial bet-hedging behavior that resembles individual-level metazoan bet hedging. Sinorhizobium meliloti stores carbon and energy in poly-3-hydroxybutyrate (PHB) as a contingency against carbon scarcity. We show that, when starved, dividing S. meliloti bet hedge by forming two daughter cells with different phenotypes. These have high and low PHB levels and are suited to long- and short-term starvation, respectively. The low-PHB cells have greater competitiveness for resources, whereas the high-PHB cells can survive for over a year without food, perhaps until a legume host is next available.
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PMID:Individual-level bet hedging in the bacterium Sinorhizobium meliloti. 2086 44

Uncovering the mechanisms underlying robust responses of cells to stress is crucial for our understanding of cellular physiology. Indeed, vast amounts of data have been collected on transcriptional responses in Saccharomyces cerevisiae. However, only a handful of pioneering studies describe the dynamics of proteins in response to external stimuli, despite the fact that regulation of protein levels and localization is an essential part of such responses. Here we characterized unprecedented proteome plasticity by systematically tracking the localization and abundance of 5,330 yeast proteins at single-cell resolution under three different stress conditions (DTT, H2O2, and nitrogen starvation) using the GFP-tagged yeast library. We uncovered a unique "fingerprint" of changes for each stress and elucidated a new response arsenal for adapting to radical environments. These include bet-hedging strategies, organelle rearrangement, and redistribution of protein localizations. All data are available for download through our online database, LOQATE (localization and quantitation atlas of yeast proteome).
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PMID:A novel single-cell screening platform reveals proteome plasticity during yeast stress responses. 2350 72

The social amoeba Dictyostelium discoideum is widely studied for its multicellular development program as a response to starvation and constitutes a model of choice in microbial cooperation studies. Aggregates of up to 10 (6) cells form fruiting bodies containing two cell types: (i) dormant spores (~80%) that can persist for months in the absence of nutrients, and (ii) dead stalk cells (~20%) that promote the dispersion of the spores towards nutrient-rich areas. It is often overlooked that not all cells aggregate upon starvation. Using a new quantitative approach based on time-lapse fluorescence microscopy and a low ratio of reporting cells, we have quantified this fraction of non-aggregating cells. In realistic starvation conditions, up to 15% of cells do not aggregate, which makes this third cell fate a significant component of the population-level response of social amoebae to starvation. Non-aggregating cells have an advantage over cells in aggregates since they resume growth earlier upon arrival of new nutrients, but have a shorter lifespan under prolonged starvation. We find that phenotypic heterogeneities linked to cell nutritional state bias the representation of cells in the aggregating vs. non-aggregating fractions, and thus regulate population partitioning. Next, we report that the fraction of non-aggregating cells depends on genetic factors that regulate the timing of starvation, signal sensing efficiency and aggregation efficiency. In addition, interactions between clones in mixtures of non-isogenic cells affect the partitioning of each clone into both fractions. We further test the evolutionary significance of the non-aggregating cell fraction. The partitioning of cells into aggregating and non-aggregating fractions is optimal in fluctuating environments with an unpredictable duration of starvation periods. D. discoideum thus constitutes a model system lying at the intersection of microbial cooperation and bet hedging, defining a new frontier in microbiology and evolution studies.
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PMID:An evolutionarily significant unicellular strategy in response to starvation stress in Dictyostelium social amoebae. 2530 31

Cellular slime molds, including the well-studied Dictyostelium discoideum, are amoebae whose life cycle includes both a single-cellular and a multicellular stage. To achieve the multicellular stage, individual amoebae aggregate upon starvation to form a fruiting body made of dead stalk cells and reproductive spores, a process that has been described in terms of cooperation and altruism. When amoebae aggregate they do not perfectly discriminate against nonkin, leading to chimeric fruiting bodies. Within chimeras, complex interactions among genotypes have been documented, which should theoretically reduce genetic diversity. This is however inconsistent with the great diversity of genotypes found in nature. Recent work has shown that a little-studied component of D. discoideum fitness--the loner cells that do not participate in the aggregation--can be selected for depending on environmental conditions and that, together with the spores, they could represent a bet-hedging strategy. We suggest that in all cellular slime molds the existence of loners could resolve the apparent diversity paradox in two ways. First, if loners are accounted for, then apparent genotypic skew in the spores of chimeras could simply be the result of different investments into spores versus loners. Second, in an ecosystem with multiple local environments differing in their food recovery characteristics and connected globally via weak-to-moderate dispersal, coexistence of multiple genotypes can occur. Finally, we argue that the loners make it impossible to define altruistic behavior, winners or losers, without a clear description of the ecology.
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PMID:Fitness tradeoffs between spores and nonaggregating cells can explain the coexistence of diverse genotypes in cellular slime molds. 2571 43

Within bacterial populations, a small fraction of persister cells is transiently capable of surviving exposure to lethal doses of antibiotics. As a bet-hedging strategy, persistence levels are determined both by stochastic induction and by environmental stimuli called responsive diversification. Little is known about the mechanisms that link the low frequency of persisters to environmental signals. Our results support a central role for the conserved GTPase Obg in determining persistence in Escherichia coli in response to nutrient starvation. Obg-mediated persistence requires the stringent response alarmone (p)ppGpp and proceeds through transcriptional control of the hokB-sokB type I toxin-antitoxin module. In individual cells, increased Obg levels induce HokB expression, which in turn results in a collapse of the membrane potential, leading to dormancy. Obg also controls persistence in Pseudomonas aeruginosa and thus constitutes a conserved regulator of antibiotic tolerance. Combined, our findings signify an important step toward unraveling shared genetic mechanisms underlying persistence.
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PMID:Obg and Membrane Depolarization Are Part of a Microbial Bet-Hedging Strategy that Leads to Antibiotic Tolerance. 2835 5

Starvation during early development can have lasting effects that influence organismal fitness and disease risk. We characterized the long-term phenotypic consequences of starvation during early larval development in Caenorhabditis elegans to determine potential fitness effects and develop it as a model for mechanistic studies. We varied the amount of time that larvae were developmentally arrested by starvation after hatching ("L1 arrest"). Worms recovering from extended starvation grew slowly, taking longer to become reproductive, and were smaller as adults. Fecundity was also reduced, with the smallest individuals most severely affected. Feeding behavior was impaired, possibly contributing to deficits in growth and reproduction. Previously starved larvae were more sensitive to subsequent starvation, suggesting decreased fitness even in poor conditions. We discovered that smaller larvae are more resistant to heat, but this correlation does not require passage through L1 arrest. The progeny of starved animals were also adversely affected: Embryo quality was diminished, incidence of males was increased, progeny were smaller, and their brood size was reduced. However, the progeny and grandprogeny of starved larvae were more resistant to starvation. In addition, the progeny, grandprogeny, and great-grandprogeny were more resistant to heat, suggesting epigenetic inheritance of acquired resistance to starvation and heat. Notably, such resistance was inherited exclusively from individuals most severely affected by starvation in the first generation, suggesting an evolutionary bet-hedging strategy. In summary, our results demonstrate that starvation affects a variety of life-history traits in the exposed animals and their descendants, some presumably reflecting fitness costs but others potentially adaptive.
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PMID:Transgenerational Effects of Early Life Starvation on Growth, Reproduction, and Stress Resistance in Caenorhabditis elegans. 2618 23

The social amoeba Dictyostelium discoideum has been recently suggested as an example of bet-hedging in microbes. In the presence of resources, amoebae reproduce as unicellular organisms. Resource depletion, however, leads to a starvation phase in which the population splits between aggregators, which form a fruiting body made of a stalk and resistant spores, and non-aggregators, which remain as vegetative cells. Spores are favored when starvation periods are long, but vegetative cells can exploit resources in environments where food replenishes quickly. The investment in aggregators versus non-aggregators can therefore be understood as a bet-hedging strategy that evolves in response to stochastic starvation times. A genotype (or strategy) is defined by the balance between each type of cells. In this framework, if the ecological conditions on a patch are defined in terms of the mean starvation time (i.e. time between the onset of starvation and the arrival of a new food pulse), a single genotype dominates each environment, which is inconsistent with the huge genetic diversity observed in nature. Here we investigate whether seasonality, represented by a periodic, wet-dry alternation in the mean starvation times, allows the coexistence of several strategies in a single patch. We study this question in a non-spatial (well-mixed) setting in which different strains compete for a common pool of resources over a sequence of growth-starvation cycles. We find that seasonality induces a temporal storage effect that can promote the stable coexistence of multiple genotypes. Two conditions need to be met in our model. First, there has to be a temporal niche partitioning (two well-differentiated habitats within the year), which requires not only different mean starvation times between seasons but also low variance within each season. Second, each season's well-adapted strain has to grow and create a large enough population that permits its survival during the subsequent unfavorable season, which requires the number of growth-starvation cycles within each season to be sufficiently large. These conditions allow the coexistence of two bet-hedging strategies. Additional tradeoffs among life-history traits can expand the range of coexistence and increase the number of coexisting strategies, contributing toward explaining the genetic diversity observed in D. discoideum. Although focused on this cellular slime mold, our results are general and may be easily extended to other microbes.
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PMID:Seasonality can induce coexistence of multiple bet-hedging strategies in Dictyostelium discoideum via storage effect. 2853 35


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