38 results found
Tiegs SD, Costello DM, Isken MW, et al., 2019, Global patterns and drivers of ecosystem functioning in rivers and riparian zones, Science Advances, Vol: 5, ISSN: 2375-2548
River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to conduct a global-scale field experiment in greater than 1000 river and riparian sites. We found that Earth’s biomes have distinct carbon processing signatures. Slow processing is evident across latitudes, whereas rapid rates are restricted to lower latitudes. Both the mean rate and variability decline with latitude, suggesting temperature constraints toward the poles and greater roles for other environmental drivers (e.g., nutrient loading) toward the equator. These results and data set the stage for unprecedented “next-generation biomonitoring” by establishing baselines to help quantify environmental impacts to the functioning of ecosystems at a global scale.
Zhang F-G, Bell T, Zhang Q-G, 2018, Experimental testing of dispersal limitation in soil bacterial communities with a propagule addition approach, Microbial Ecology, ISSN: 0095-3628
The role of dispersal in the assembly of microbial communities remains contentious. This study tested the importance of dispersal limitation for the structuring of local soil bacterial communities using an experimental approach of propagule addition. Microbes extracted from soil pooled from samples collected at 20 localities across ~ 400 km in a temperate steppe were added to microcosms of local soils at three sites; the microcosms were then incubated in situ for 3 months. We then assessed the composition and diversity of bacterial taxa in the soils using 16S rRNA gene amplicon sequencing. The addition of the regional microbial pool did not cause significant changes in the overall composition or diversity of the total bacterial community, although a very small number of individual taxa may have been affected by the addition treatment. Our results suggest a negligible role of dispersal limitation in structuring soil bacterial communities in our study area.
Rivett DW, Bell T, 2018, Abundance determines the functional role of bacterial phylotypes in complex communities, NATURE MICROBIOLOGY, Vol: 3, Pages: 767-+, ISSN: 2058-5276
Rivett D, Jones M, Ramoneda J, et al., 2018, Elevated success of multispecies bacterial invasions impacts community composition during ecological succession, Ecology Letters, Vol: 21, Pages: 516-524, ISSN: 1461-023X
Successful microbial invasions are determined by a species’ ability to occupy a niche in the new habitat whilst resisting competitive exclusion by the resident community. Despite the recognised importance of biotic factors in determining the invasiveness of microbial communities, the success and impact of multiple concurrent invaders on the resident community has not been examined. Simultaneous invasions might have synergistic effects, for example if resident species need to exhibit divergent phenotypes to compete with the invasive populations. We used three phylogenetically diverse bacterial species to invade two compositionally distinct communities in a controlled, naturalised in vitro system. By initiating the invader introductions at different stages of succession, we could disentangle the relative importance of resident community structure, invader diversity and time pre‐invasion. Our results indicate that multiple invaders increase overall invasion success, but do not alter the successional trajectory of the whole community.
Jones ML, Ramoneda JM, Rivett DW, et al., 2017, Biotic resistance shapes the influence of propagule pressure on invasion success in bacterial communities, Ecology, ISSN: 1939-9170
The number of invaders and the timing of invasion are recognized as key determinants of successful invasions. Despite the recognized importance of “propagule pressure,” invasion ecology has largely focused on how characteristics of the native community confer invasion resistance. We simultaneously manipulated community composition and invader propagule pressure in microcosm communities of freshwater bacteria. We show that high propagule pressures can be necessary to establish an invader population, but that the influence of propagule pressure depends on the composition of the resident species. In particular, the number of individuals invading was most important to invasion success when one of the species in a resident community is a strong competitor against other species. By contrast, the timing of invasion was most important when communities had lower growth rates. The results suggest that the importance of propagule pressure varies both between communities and within the same community over time, and therefore have implications for the way we understand the relationship between biotic resistance and invasion success.
Bell T, Tylianakis JM, 2016, Microbes in the Anthropocene: spillover of agriculturally selected bacteria and their impact on natural ecosystems, Proceedings of the Royal Society B: Biological Sciences, Vol: 283, ISSN: 0962-8452
Soil microbial communities are enormously diverse, with at least millions of species and trillions of genes unknown to science or poorly described. Soil microbial communities are key components of agriculture, for example in provisioning nitrogen and protecting crops from pathogens, providing overall ecosystem services in excess of $1000bn per year. It is important to know how humans are affecting this hidden diversity. Much is known about the negative consequences of agricultural intensification on higher-organisms, but almost nothing is known about how alterations to landscapes affect microbial diversity, distributions and processes. Wereview what is known about spatial flows of microbes and their response to land use change, and outline nine hypotheses to advance research of microbiomes across landscapes. We hypothesise that intensified agriculture selects for certain taxa and genes, which then “spill over” into adjacent unmodified areas and generate a halo of genetic differentiation around agricultural fields.Consequently, the spatial configuration and management intensityof different habitats combines with the dispersal ability of individual taxa to determine the extent of spillover, which canimpact the functioning of adjacent unmodified habitats. When landscapes are heterogeneous and dispersal rates are high, this will select for large genomes that allow exploitation of multiple habitats, a process that may be accelerated through horizontal gene transfer.Continued expansion of agriculture will increase genotypic similarity, making microbial community functioning increasingly variable in human-dominated landscapes, potentially also impactingthe consistent provisioning of ecosystem services.While the resulting economic costs have not been calculated, it is clear that dispersal dynamics of microbes s
Lehmann K, Bell T, Bowes MJ, et al., 2016, Trace levels of sewage effluent are sufficient to increase class 1 integron prevalence in freshwater biofilms without changing the core community, WATER RESEARCH, Vol: 106, Pages: 163-170, ISSN: 0043-1354
Dupont AOC, Griffiths RI, Bell T, et al., 2016, Differences in soil micro-eukaryotic communities over soil pH gradients are strongly driven by parasites and saprotrophs, ENVIRONMENTAL MICROBIOLOGY, Vol: 18, Pages: 2010-2024, ISSN: 1462-2912
Barraclough TG, Bell TDC, Rivett D, et al., 2016, Resource-dependent attenuation of species interactions during bacterial succession, ISME Journal, Vol: 10, Pages: 2259-2268, ISSN: 1751-7362
Bacterial communities are vital for many economically and ecologically important processes. The role of bacterial community composition in determining ecosystem functioning depends critically on interactions among bacterial taxa. Several studies have shown that, despite a predominance of negative interactions in communities, bacteria are able to display positive interactions given the appropriate evolutionary or ecological conditions. We were interested in how interspecific interactions develop over time in a naturalistic setting of low resource supply rates. We assembled aquatic bacterial communities in microcosms and assayed the productivity (respiration and growth) and substrate degradation while tracking community composition. The results demonstrated that while bacterial communities displayed strongly negative interactions during the early phase of colonisation and acclimatisation to novel biotic and abiotic factors, this antagonism declined over time towards a more neutral state. This was associated with a shift from use of labile substrates in early succession to use of recalcitrant substrates later in succession, confirming a crucial role of resource dynamics in linking interspecific interactions with ecosystem functioning.
Fisher RM, Bell T, West SA, 2016, Multicellular group formation in response to predators in the alga Chlorella vulgaris, Journal of Evolutionary Biology, Vol: 29, Pages: 551-559, ISSN: 1420-9101
A key step in the evolution of multicellular organisms is the formation of cooperative multicellular groups. It has been suggested that predation pressure may promote multicellular group formation in some algae and bacteria, with cells forming groups to lower their chance of being eaten. We use the green alga Chlorella vulgaris and the protist Tetrahymena thermophila to test whether predation pressure can initiate the formation of colonies. We found that: (1) either predators or just predator exoproducts promote colony formation; (2) higher predator densities cause more colonies to form; and (3) colony formation in this system is facultative, with populations returning to being unicellular when the predation pressure is removed. These results provide empirical support for the hypothesis that predation pressure promotes multicellular group formation. The speed of the reversion of populations to unicellularity suggests that this response is due to phenotypic plasticity and not evolutionary change.
Barraclough TG, Lawrence D, Bell T, 2015, The effect of immigration on the adaptation of microbial communities to warming, American Naturalist, Vol: 187, ISSN: 1537-5323
Theory predicts that immigration can either enhance or impair the rate at which species and whole communities adapt to environmental change, depending on the traits of genotypes and species in the source pool relative to local conditions. These responses in turn will determine how well whole communities function in changing environments. We tested the effects of immigration and experimental warming on microbial communities during an 81 day field experiment. The effects of immigration depended on the warming treatment. In warmed communities immigration was detrimental to community growth whereas in ambient communities it was beneficial. This result is explained if colonists came from a local species pool pre-adapted to ambient conditions. Loss of metabolic diversity, however, was buffered by immigration in both environments. Communities showed increasing local adaptation to temperature conditions during the experiment and this was independent of whether or not they received immigration. Genotypes that comprised the communities were not locally adapted, however, indicating that community local adaptation can be independent of adaptation of component genotypes. Our results are consistent with a greater role for species interactions rather than adaptation of constituent species in determining local adaptation of whole communities, and confirm that immigration can either enhance or impair community responses to environmental change depending on the environmental context.
Lehmann K, Singer A, Bowes MJ, et al., 2015, 16S rRNA assessment of the influence of shading on early-successional biofilms in experimental streams, FEMS MICROBIOLOGY ECOLOGY, Vol: 91, ISSN: 0168-6496
Slade EM, Roslin T, Santalahti M, et al., 2015, Disentangling the "brown world' faecal-detritus interaction web: dung beetle effects on soil microbial properties, Oikos, Vol: 125, Pages: 629-635, ISSN: 0030-1299
Many ecosystem services are sustained by the combined action of microscopic and macroscopic organisms, and shaped by interactions between the two. However, studies tend to focus on only one of these two components. We combined the two by investigating the impact of macrofauna on microbial community composition and functioning in the context of a major ecosystem process: the decomposition of dung. We compared bacterial communities of pasture soil and experimental dung pats inhabited by one (Aphodius), two (Aphodius and Geotrupes), or no dung beetle genera. Overall, we found distinct microbial communities in soil and dung samples, and that the communities converged over the course of the experiment. Characterising the soil microbial communities underlying the dung pats revealed a signiﬁcant interactive eﬀect between the microﬂora and macrofauna, where the diversity and composition of microbial communities was signiﬁcantly aﬀected by the presence or absence of dung beetles. e speciﬁc identity of the beetles had no detectable impact, but the microbial evenness was lower in the presence of both Aphodius and Geotrupes than in the presence of Aphodius alone. Diﬀerences in microbial community composition were associated with diﬀerences in substrate usage as measured by Ecoplates. More-over, microbial communities with similar compositions showed more similar substrate usage. Our study suggests that the presence of macrofauna (dung beetles) will modify the microﬂora (bacteria) of both dung pats and pasture soil, including community diversity and functioning. In particular, the presence of dung beetles promotes the transfer of bacteria across the soil–dung interface, resulting in increased similarity in community structure and functioning. e results demonstrate that to understand how microbes contribute to the ecosystem process of dung decomposition, there is a need to understand their interactions with larger co-occurring fauna.
Barraclough TG, Bell T, Scheuerl T, 2015, Saturating effects of species diversity on life-history evolution in bacteria, Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol: 282, ISSN: 0080-4649
Species interactions can play a major role in shaping evolution in new environments. In theory, species interactions can either stimulate evolution by promoting coevolution or inhibit evolution by constraining ecological opportunity. The relative strength of these effects should vary as species richness increases, and yet there has been little evidence for evolution of component species in communities. We evolved bacterial microcosms containing between 1 and 12 species in three different environments. Growth rates and yields of isolates that evolved in communities were lower than those that evolved in monocultures, consistent with recent theory that competition constrains species to specialize on narrower sets of resources. This effect saturated or reversed at higher levels of richness, consistent with theory that directional effects of species interactions should weaken in more diverse communities. Species varied considerably, however, in their responses to both environment and richness levels. Mechanistic models and experiments are now needed to understand and predict joint evolutionary dynamics of species in diverse communities.
Friman V-P, Guzman LM, Reuman DC, et al., 2015, Bacterial adaptation to sublethal antibiotic gradients can change the ecological properties of multitrophic microbial communities, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 282, ISSN: 0962-8452
Fiegna F, Moreno-Letelier A, Bell T, et al., 2015, Evolution of species interactions determines microbial community productivity in new environments, ISME JOURNAL, Vol: 9, Pages: 1235-1245, ISSN: 1751-7362
Samani P, Low-Decarie E, McKelvey K, et al., 2015, Metabolic variation in natural populations of wild yeast, ECOLOGY AND EVOLUTION, Vol: 5, Pages: 722-732, ISSN: 2045-7758
Connolly J, Bell T, Bolger T, et al., 2013, An improved model to predict the effects of changing biodiversity levels on ecosystem function, JOURNAL OF ECOLOGY, Vol: 101, Pages: 344-355, ISSN: 0022-0477
Foster K, Bell T, 2012, Competition, Not Cooperation, Dominates Interactions among Culturable Microbial Species, Current Biology, Vol: 22, Pages: 1845-1850
Microbial cells secrete numerous enzymes, scavenging molecules, and signals that can promote the growth and survival of other cells around them [ , ,  and ]. This observation is consistent with the evolution of cooperation within species , and there is now an increasing emphasis on the importance of cooperation between different microbial species [ ,  and ]. We lack, however, a systematic test of the importance of mutually positive interactions between different species, which is vital for assessing the commonness and importance of cooperative evolution in natural communities. Here, we study the extent of mutually positive interaction among bacterial strains isolated from a common aquatic environment. Using data collected from two independent experiments evaluating community productivity across diversity gradients, we show that (1) in pairwise species combinations, the great majority of interactions are net negative and (2) there is no evidence that strong higher-order positive effects arise when more than two species are mixed together. Our data do not exclude the possibility of positive effects in one direction where one species gains at the expense of another, i.e., predator-prey-like interactions. However, these do not constitute cooperation and our analysis suggests that the typical result of adaptation to other microbial species will be competitive, rather than cooperative, phenotypes.
Lawrence D, Fiegna F, Behrends V, et al., 2012, Species interactions alter evolutionary responses to a novel environment., PLoS Biol, Vol: 10
Studies of evolutionary responses to novel environments typically consider single species or perhaps pairs of interacting species. However, all organisms co-occur with many other species, resulting in evolutionary dynamics that might not match those predicted using single species approaches. Recent theories predict that species interactions in diverse systems can influence how component species evolve in response to environmental change. In turn, evolution might have consequences for ecosystem functioning. We used experimental communities of five bacterial species to show that species interactions have a major impact on adaptation to a novel environment in the laboratory. Species in communities diverged in their use of resources compared with the same species in monocultures and evolved to use waste products generated by other species. This generally led to a trade-off between adaptation to the abiotic and biotic components of the environment, such that species evolving in communities had lower growth rates when assayed in the absence of other species. Based on growth assays and on nuclear magnetic resonance (NMR) spectroscopy of resource use, all species evolved more in communities than they did in monocultures. The evolutionary changes had significant repercussions for the functioning of these experimental ecosystems: communities reassembled from isolates that had evolved in polyculture were more productive than those reassembled from isolates that had evolved in monoculture. Our results show that the way in which species adapt to new environments depends critically on the biotic environment of co-occurring species. Moreover, predicting how functioning of complex ecosystems will respond to an environmental change requires knowing how species interactions will evolve.
Gravel D, Bell T, Barbera C, et al., 2012, Phylogenetic constraints on ecosystem functioning, Nature Communications, Vol: 3
There is consensus that biodiversity losses will result in declining ecosystem functioning if species have different functional traits. Phylogenetic diversity has recently been suggested as a predictor of ecosystem functioning because it could approximate the functional complementarity among species. Here we describe an experiment that takes advantage of the rapid evolutionary response of bacteria to disentangle the role of phylogenetic and species diversity. We impose a strong selection regime on marine bacterial lineages and assemble the ancestral and evolved lines in microcosms of varying lineage and phylogenetic diversity. We find that the relationship between phylogenetic diversity and productivity is strong for the ancestral lineages but brakes down for the evolved lineages. Our results not only emphasize the potential of using phylogeny to evaluate ecosystem functioning, but also they warn against using phylogenetics as a proxy for functional diversity without good information on species evolutionary history
Poisot T, Bell T, Martinez E, et al., 2012, Terminal investment induced by a bacteriophage in a rhizosphere bacterium., F1000Res, Vol: 1, ISSN: 2046-1402
Despite knowledge about microbial responses to abiotic stress, few studies have investigated stress responses to antagonistic species, such as competitors, predators and pathogens. While it is often assumed that interacting populations of bacteria and phage will coevolve resistance and exploitation strategies, an alternative is that individual bacteria tolerate or evade phage predation through inducible responses to phage presence. Using the microbial model Pseudomonas fluorescens SBW25 and its lytic DNA phage SBW25Φ2, we demonstrate the existence of an inducible response in the form of a transient increase in population growth rate, and found that the response was induced by phage binding. This response was accompanied by a decrease in bacterial cell size, which we propose to be an associated cost. We discuss these results in the context of bacterial ecology and phage-bacteria co-evolution.
Poroyko V, Morowitz M, Bell T, et al., 2011, Diet creates metabolic niches in the "inmature gut" that shape microbial communities, NUTRICION HOSPITALARIA, Vol: 26, Pages: 1283-1295, ISSN: 0212-1611
Barrett LG, Bell T, Dwyer G, et al., 2011, Cheating, trade-offs and the evolution of aggressiveness in a natural pathogen population, Ecology Letters, Vol: 14, Pages: 1149-1157
The evolutionary dynamics of pathogens are critically important for disease outcomes, prevalence and emergence. In this study we investigate ecological conditions that may promote the long-term maintenance of virulence polymorphisms in pathogen populations. Recent theory predicts that evolution towards increased virulence can be reversed if less-aggressive social 'cheats' exploit more aggressive 'cooperator' pathogens. However, there is no evidence that social exploitation operates within natural pathogen populations. We show that for the bacterium Pseudomonas syringae, major polymorphisms for pathogenicity are maintained at unexpectedly high frequencies in populations infecting the host Arabidopsis thaliana. Experiments reveal that less-aggressive strains substantially increase their growth potential in mixed infections and have a fitness advantage in non-host environments. These results suggest that niche differentiation can contribute to the maintenance of virulence polymorphisms, and that both within-host and between-host growth rates modulate cheating and cooperation in P. syringae populations.
Griffiths RI, Thomson BC, James P, et al., 2011, The bacterial biogeography of British soils, Vol: 13, Pages: 1642-1654, ISSN: 1462-2920
Gravel D, Bell T, Barbera C, et al., 2011, Experimental niche evolution alters the strength of the diversity-productivity relationship, Vol: 469, Pages: 89-92, ISSN: 0028-0836
The relationship between biodiversity and ecosystem functioning (BEF) has become a cornerstone of community and ecosystem ecology(1-3) and an essential criterion for making decisions in conservation biology and policy planning(4,5). It has recently been proposed that evolutionary history should influence the BEF relationship because it determines species traits and, thus, species' ability to exploit resources(6,7). Here we test this hypothesis by combining experimental evolution with a BEF experiment. We isolated 20 bacterial strains from a marine environment and evolved each to be generalists or specialists(8). We then tested the effect of evolutionary history on the strength of the BEF relationship with assemblages of 1 to 20 species constructed from the specialists, generalists and ancestors(9). Assemblages of generalists were more productive on average because of their superior ability to exploit the environmental heterogeneity(10). The slope of the BEF relationship was, however, stronger for the specialist assemblages because of enhanced niche complementarity. These results show how the BEF relationship depends critically on the legacy of past evolutionary events.
Gluecksman E, Bell T, Griffiths RI, et al., 2010, Closely related protist strains have different grazing impacts on natural bacterial communities, ENVIRONMENTAL MICROBIOLOGY, Vol: 12, Pages: 3105-3113, ISSN: 1462-2912
Bell T, 2010, Experimental tests of the bacterial distance-decay relationship, Vol: 4, Pages: 1357-1365, ISSN: 1751-7362
Bell T, Bonsall MB, Buckling A, et al., 2010, Protists have divergent effects on bacterial diversity along a productivity gradient, Vol: 6, Pages: 639-642, ISSN: 1744-9561
Productivity and predation are thought to be crucial drivers of bacterial diversity. We tested how the productivity-diversity of a natural bacterial community is modified by the presence of protist predators with different feeding preferences. In the absence of predators, there was a unimodal relationship between bacterial diversity and productivity. We found that three protist species (Bodo, Spumella and Cyclidium) had widely divergent effects on bacterial diversity across the productivity gradient. Bodo and Cyclidium had little effect on the shape of the productivity-diversity gradient, while Spumella flattened the relationship. We explain these results in terms of the feeding preferences of these predators.
Srivastava DS, Bell T, 2009, Reducing horizontal and vertical diversity in a foodweb triggers extinctions and impacts functions, Vol: 12, Pages: 1016-1028
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