Antibiotic stress selects against cooperation in the pathogenic bacterium Pseudomonas aeruginosa

Cheats are a pervasive threat to public goods production in natural and human communities, as they benefit from the commons without contributing to it. Although ecological antagonisms such as predation, parasitism, competition, and abiotic environmental stress play key roles in shaping population biology, it is unknown how such stresses generally affect the ability of cheats to undermine cooperation. We used theory and experiments to address this question in the pathogenic bacterium, Pseudomonas aeruginosa Although public goods producers were selected against in all populations, our competition experiments showed that antibiotics significantly increased the advantage of nonproducers. Moreover, the dominance of nonproducers in mixed cultures was associated with higher resistance to antibiotics than in either monoculture. Mathematical modeling indicates that accentuated costs to producer phenotypes underlie the observed patterns. Mathematical analysis further shows how these patterns should generalize to other taxa with public goods behaviors. Our findings suggest that explaining the maintenance of cooperative public goods behaviors in certain natural systems will be more challenging than previously thought. Our results also have specific implications for the control of pathogenic bacteria using antibiotics and for understanding natural bacterial ecosystems, where subinhibitory concentrations of antimicrobials frequently occur

Contrasted Effects of Diversity and Immigration on Ecological Insurance in Marine Bacterioplankton Communities

The ecological insurance hypothesis predicts a positive effect of species richness on ecosystem functioning in a variable environment. This effect stems from temporal and spatial complementarity among species within metacommunities coupled with optimal levels of dispersal. Despite its importance in the context of global change by human activities, empirical evidence for ecological insurance remains scarce and controversial. Here we use natural aquatic bacterial communities to explore some of the predictions of the spatial and temporal aspects of the ecological insurance hypothesis. Addressing ecological insurance with bacterioplankton is of strong relevance given their central role in fundamental ecosystem processes. Our experimental set up consisted of water and bacterioplankton communities from two contrasting coastal lagoons. In order to mimic environmental fluctuations, the bacterioplankton community from one lagoon was successively transferred between tanks containing water from each of the two lagoons. We manipulated initial bacterial diversity for experimental communities and immigration during the experiment. We found that the abundance and production of bacterioplankton communities was higher and more stable (lower temporal variance) for treatments with high initial bacterial diversity. Immigration was only marginally beneficial to bacterial communities, probably because microbial communities operate at different time scales compared to the frequency of perturbation selected in this study, and of their intrinsic high physiologic plasticity. Such local “physiological insurance” may have a strong significance for the maintenance of bacterial abundance and production in the face of environmental perturbations

Novel loci for childhood body mass index and shared heritability with adult cardiometabolic traits

The genetic background of childhood body mass index (BMI), and the extent to which the well-known associations of childhood BMI with adult diseases are explained by shared genetic factors, are largely unknown. We performed a genome-wide association study meta-analysis of BMI in 61,111 children aged between 2 and 10 years. Twenty-five independent loci reached genome-wide significance in the combined discovery and replication analyses. Two of these, located nearNEDD4LandSLC45A3, have not previously been reported in relation to either childhood or adult BMI. Positive genetic correlations of childhood BMI with birth weight and adult BMI, waist-to-hip ratio, diastolic blood pressure and type 2 diabetes were detected (R(g)ranging from 0.11 to 0.76, P-values Author summary Although twin studies have shown that body mass index (BMI) is highly heritable, many common genetic variants involved in the development of BMI have not yet been identified, especially in children. We studied associations of more than 40 million genetic variants with childhood BMI in 61,111 children aged between 2 and 10 years. We identified 25 genetic variants that were associated with childhood BMI. Two of these have not been implicated for BMI previously, located close to the genesNEDD4LandSLC45A3. We also show that the genetic background of childhood BMI overlaps with that of birth weight, adult BMI, waist-to-hip-ratio, diastolic blood pressure, type 2 diabetes, and age at menarche. Our results suggest that the biological processes underlying childhood BMI largely overlap with those underlying adult BMI. However, the overlap is not complete. Additionally, the genetic backgrounds of childhood BMI and other cardio-metabolic phenotypes are overlapping. This may mean that the associations of childhood BMI and later cardio-metabolic outcomes are partially explained by shared genetics, but it could also be explained by the strong association of childhood BMI with adult BMI.Peer reviewe

Ecological strategies shape the insurance potential of biodiversity

International audienc

Data from: Evolutionary dynamics of separate and combined exposure of Pseudomonas fluorescens SBW25 to antibiotics and bacteriophage

The use of bacteriophages against pathogenic bacteria in health care and in the food industry is now being advocated as an alternative to the use of antibiotics. But what is the evolutionary response for a bacterial population if both antibiotics and phages are used in combination? We employ an experimental evolution approach to address these questions and exposed Pseudomonas fluorescens SBW25 and a related hypermutator strain (mutS-) to the action of the antibiotic rifampicin and the lytic bacteriophage SBW25φ2. We then compared the densities, growth rates, and the mutations at the rpoB locus leading to rifampicin resistance of the evolved bacterial populations. We observed that the evolutionary response of populations under different treatments varied depending on the order in which the antimicrobials were added and whether the bacterium was a hypermutator. We found that wild type rifampicin-resistant populations involved in biofilm formation often reverted to rifampicin sensitivity when stresses were added sequentially. In contrast, when the mortality agents were added simultaneously, phage populations frequently went extinct and the bacteria evolved antibiotic resistance. Finally, populations of the hypermutator mutS- converged to a single genotype at the rpoB locus. Future investigation on other bacteria and using different antibiotics and bacteriophage are needed to evaluate the generality of our findings

Evolutionary rescue and local adaptation under different rates of temperature increase: a combined analysis of changes in phenotype expression and genotype frequency in Paramecium microcosms

International audienceEvolutionary rescue (ER) occurs when populations, which have declined due to rapid environmental change, recover through genetic adaptation. The success of this process and the evolutionary trajectory of the population strongly depend on the rate of environmental change. Here we investigated how different rates of temperature increase (from 23 to 32 °C) affect population persistence and evolutionary change in experimental microcosms of the protozoan Paramecium caudatum. Consistent with theory on ER, we found that those populations experiencing the slowest rate of temperature increase were the least likely to become extinct and tended to be the best adapted to the new temperature environment. All high-temperature populations were more tolerant to severe heat stress (35, 37 °C), indicating a common mechanism of heat protection. High-temperature populations also had superior growth rates at optimum temperatures, leading to the absence of a pattern of local adaptation to control (23 °C) and high-temperature (32 °C) environments. However, high-temperature populations had reduced growth at low temperatures (5-9 °C), causing a shift in the temperature niche. In part, the observed evolutionary change can be explained by selection from standing variation. Using mitochondrial markers, we found complete divergence between control and high-temperature populations in the frequencies of six initial founder genotypes. Our results confirm basic predictions of ER and illustrate how adaptation to an extreme local environment can produce positive as well as negative correlated responses to selection over the entire range of the ecological niche

Predicting biotic interactions and their variability in a changing environment

International audienceGlobal environmental change is altering the patterns of biodiversity worldwide. Observation and theory suggest that species' distributions and abundances depend on a suite of processes, notably abiotic filtering and biotic interactions, both of which are constrained by species' phylogenetic history. Models predicting species distribution have historically mostly considered abiotic filtering and are only starting to integrate biotic interaction. However, using information on present interactions to forecast the future of biodiversity supposes that biotic interactions will not change when species are confronted with new environments. Using bacterial microcosms, we illustrate how biotic interactions can vary along an environmental gradient and how this variability can depend on the phylogenetic distance between interacting species

Predicting evolution in experimental range expansions of an aquatic model system

Abstract Predicting range expansion dynamics is a challenge for both fundamental and applied research in conservation and global change biology. However, if ecological and evolutionary processes occur on the same time scale, predictions are challenging to make. Combining experimental evolution and mathematical modelling, we assessed the predictability of independent realisations of range expansions in a laboratory model system, the freshwater protozoan Paramecium caudatum . We followed ecological dynamics and evolutionary change in range core and front populations in the experiment. These settings were recreated in a predictive mathematical model, parametrized with dispersal and growth data of the of the 20 founder strains in the experiment. We find that short-term evolution was driven by selection for increased dispersal at the front and general selection for higher growth rates in all treatments. There was a good quantitative match of predicted and observed trait changes. Phenotypic divergence was mirrored by a complete genotypic divergence, indicating the highly repeatable fixation of strains that also were the most likely winners in our model. Long-term evolution in the experimental range front lines resulted in the emergence of a dispersal syndrome, namely a competition - colonisation trade-off. Altogether, both model and experiment highlight the importance of dispersal evolution as a driver of range expansions. Our study suggests that evolution at range fronts may follow predictable trajectories, at least for simple scenarios, and that predicting these dynamics may be possible from knowledge of few key parameters

Evaluación geotécnica para la construcción de la presa Huanzo

TesisEsta investigación trata de la evaluación geotécnica de la zona de emplazamiento y material de préstamo para una presa de tierra cuyo almacenamiento es con fines de irrigación y con una capacidad de almacenamiento de 13’000,000 m 3 . El área de estudio se localiza en el distrito de Santiago de Lucanamarca, provincia de Huancasancos, departamento de Ayacucho. Los objetivos de la investigación son: caracterizar los parámetros geotécnicos, análisis de estabilidad de talud de la presa, infiltración en el cuerpo y lugar de desplante de presa, en los cuales se realizaron trabajos de exploración geotécnica tales como mapeo geológico local, prospección geofísica, perforaciones diamantinas, excavación de calicatas, ensayos in situ de permeabilidad, ensayos de laboratorio y determinar el diseño de la geometría apropiado para la construcción de la presa. La metodología empleada es el cuantitativo, además de descriptivo, las técnicas de estudio conciernen a actividades de campo, laboratorio y gabinete con el fin de cuantificar los parámetros geotécnicos. Geológicamente el área presenta terrenos morrénicos (arenas limosas con bloques y material aluvial). Geomorfológicamente presenta relieves de pendiente suave a poco empinados. Los parámetros geotécnicos del cuerpo de presa corresponden a una clasificación SUCS arena limosa con gravas (SMGM), su resistencia corresponde a un ángulo de fricción 42.4º, cohesión 0.36 kg/cm 2 y una permeabilidad promedio de 4.44xE-5 cm/s. Para el presente caso, el diseño de presa es: 12 m. de altura, 5 m. de coronación, taludes 1V/2H aguas arriba, 1V/1.8H aguas abajo, con un filtro horizontal de 15 m. Los parámetros geotécnicos para el lugar de cimentacion son: clasificación SUCS arena limosa (SM), la resistencia corresponde a una cohesión de 0.34 Kg/ cm 2 , ángulo de fricción 33.7° y una permehabilidad de 7.96E05 cm/s. Se hará un tratamiento con geosintético en la pantalla aguas arriba y tres líneas de inyecciones de cemento en el pie del talud aguas arriba. Se obtuvieron parámetros geotécnicos apropiados para su construcción, por lo cual la presa es estable debido a los factores de seguridad obtenidos; aguas arriba 2.181, aguas abajo 1.713 y para un desembalse rápido 1.416, utilizando el coeficiente sísmico 0.22 g. La infiltración obtenida con el tratamiento en la sección del eje de presa se redujo de 0.38 m 3 /hora a 0.11 m 3 /hora, en la zona del pie de talud aguas arriba se redujo de 0.43 m 3 /hora a 0.15 m 3 /hora

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