Biology subjects

Clegg, T.

Publications and source records attributed to Clegg, T..

5 recordsLinked to original sources

bioRxiv2023

Bacterial responses to complex mixtures of chemical pollutants

Our understanding of how microbes respond to pollutants is almost wholly based on single-species responses to individual chemicals. However, in natural environments, microbes experience the effects of multiple pollutants simultaneously, and their responses to these mixtures of chemicals may not be readily predictable based on their responses to each pollutant in isolation. Here we extended the scope and complexity of previous multi-stressor experiments by assaying the growth of model and non-model strains of bacteria in all 255 combinations of 8 chemical stressors. This approach allowed us to identify fitness effects arising from potential high-order interactions among stressor responses. We found that the bacterial strains responded in different ways to stressor mixtures, which could not be predicted simply from their phylogenetic relatedness. Responses to increasingly complex chemical mixtures were more likely to show a significant deviation from a null model based on the responses to each chemical alone. However, these net responses were mainly driven by lower-order interactions among a small number of chemicals, suggesting a limited role for complex high-order interactions. These results simplify the predictability of microbial populations and communities responding to multiple stressors, paving the way for the development of efficient next-generation eco-toxicological assays.

microbiology↗

bioRxiv2022

Variation in thermal physiology can drive the temperature-dependence of microbial community richness

Predicting how species diversity changes along environmental gradients is an enduring problem in ecology. Current theories cannot explain the observation that microbial taxonomic richness can show positive, unimodal, as well as negative diversity-temperature gradients. Here we derive a general empirically-grounded theory that can explain this phenomenon by linking microbial species richness in local communities to variation in their temperature-driven competitive interaction and growth rates. It predicts that richness depends on variation in shape of the thermal performance curves of these metabolic traits across species in the community. Specifically, the shape of the microbial community temperature-richness relationship depends on how the strength of competition across the community and the degree of variation in growth rates changes across temperature. These in turn can be predicted from the variation in thermal performance across the community. We show that empirical variation in the thermal performance curves of metabolic traits across extant bacterial taxa is indeed sufficient to generate the variety of community-level temperature-richness responses observed in the real world. Our results provide a new mechanism that can help explain temperature-diversity gradients in microbial communities, and provide a quantitative framework for interlinking variation in the thermal physiology of microbial species to their community-level diversity.

ecology↗

bioRxiv2021

The role of competition versus cooperation in microbial community coalescence

New microbial communities often arise through the mixing of two or more separately assembled parent communities, a phenomenon that has been termed "community coalescence". Understanding how the interaction structures of complex parent communities determine the outcomes of coalescence events is an important challenge. While recent work has begun to elucidate the role of competition in coalescence, that of cooperation, a key interaction type commonly seen in microbial communities, is still largely unknown. Here, using a general consumer-resource model, we study the combined effects of competitive and cooperative interactions on the outcomes of coalescence events. In order to do so, we simulate coalescence events between pairs of communities with different degrees of competition for shared carbon resources and cooperation through cross-feeding on leaked metabolic by-products (facilitation). We also study how structural and functional properties of post-coalescence communities evolve when they are subjected to repeated coalescence events. We find that in coalescence events, the less competitive and more cooperative parent communities contribute a higher proportion of species to the new community, because this endows superior ability to deplete resources and resist invasions. Consequently, when a community is subjected to repeated coalescence events, it gradually evolves towards being less competitive and more cooperative, as well as more species rich, robust and efficient in resource use. Encounters between microbial communities are becoming increasingly frequent as a result of anthropogenic environmental change, and there is great interest in how the coalescence of microbial communities affects environmental and human health. Our study provides new insights into the mechanisms behind microbial community coalescence, and a framework to predict outcomes based on the interaction structures of parent communities. Author summaryIn nature, new microbial communities often arise from the fusion of whole, previously separate communities (community coalescence). Despite the crucial role that interactions among microbes play in the dynamics of complex communities, our ability to predict how these affect the outcomes of coalescence events remains limited. Here, using a general mathematical model, we study how the structure of species interactions confers an advantage upon a microbial community when it encounters another, and how communities evolve after undergoing repeated coalescence events. We find that competitive interactions between species preclude their survival upon a coalescence event, while cooperative interactions are advantageous for post-coalescence survival. Furthermore, after a community is exposed to many coalescence events, the remaining species become less competitive and more cooperative. Ultimately, this drives the community evolution, yielding post-coalescence communities that are more species-rich, productive, and resistant to invasions. There are many potential environmental and health implications of microbial community coalescence, which will benefit from the theoretical insights that we offer here about the fundamental mechanisms underlying this phenomenon.

ecology↗

bioRxiv2021

Species interactions amplify the temperature dependence of microbial community respiration

The respiratory release of CO2 by microbes is a dominant component of the global carbon cycle. However, large uncertainties exist about the effects of climatic warming on the respiration of microbial communities due to lack of mechanistic, empirically-tested theory that accounts for dynamic species interactions. We developed a general mathematical model which predicts that thermal sensitivity of microbial community respiration increases as species interactions become more positive, i.e., change from competition to facilitation. This is because facilitation disproportionately increases positive feedbacks between the thermal sensitivities of species-level metabolic and biomass accumulation rates at warmer temperatures. We experimentally validated this prediction in bacterial communities of 8 taxa, finding that a shift from competition to facilitation after a month of co-adaptation caused a 60% increase in the thermal sensitivity of their respiration relative to de novo communities that had not co-adapted. Thus, rapid changes in species interactions can profoundly change the temperature-dependence of microbial community respiration and should be considered in climate change models.

ecology↗

bioRxiv2020

Systematic variation in the temperature dependence of bacterial carbon use efficiency

Understanding the temperature dependence of carbon use efficiency (CUE) is critical for understanding microbial physiology, population dynamics, and community-level responses to changing environmental temperatures 1,2. Currently, microbial CUE is widely assumed to decrease with temperature 3,4. However, this assumption is based largely on community-level data, which are influenced by many confounding factors 5, with little empirical evidence at the level of individual strains. Here, we experimentally characterise the CUE thermal response for a diverse set of environmental bacterial isolates. We find that contrary to current thinking, bacterial CUE typically responds either positively to temperature, or has no discernible temperature response, within biologically meaningful temperature ranges. Using a global data-synthesis, we show that our empirical results are generalisable across a much wider diversity of bacteria than have previously been tested. This systematic variation in the thermal responses of bacterial CUE stems from the fact that relative to respiration rates, bacterial population growth rates typically respond more strongly to temperature, and are also subject to weaker evolutionary constraints. Our results provide fundamental new insights into microbial physiology, and a basis for more accurately modelling the effects of shorter-term thermal fluctuations as well as longer-term climatic warming on microbial communities.

microbiology↗