Biology subjects

Bloxham, B.

Publications and source records attributed to Bloxham, B..

3 recordsLinked to original sources

bioRxiv2024

Repulsion from slow-diffusing nutrients improves chemotaxis towards moving sources

Chemotaxis, or the following of chemical concentration gradients, is essential for microbes to locate nutrients. However, microbes often display paradoxical behaviors, such as Escherichia coli being repelled by several amino acids. Here, we explore chemotaxis towards a moving source and demonstrate that when multiple nutrients are released from the source repulsion from certain nutrients actually improves chemotaxis towards the source. Because a moving source leaves most of the nutrient plume behind it, simply following the concentration gradient results in aiming behind the source and failing to intercept it. However, when attraction to a fast-diffusing nutrient and repulsion from a slow-diffusing nutrient are combined, motion in a new direction emerges and the chance of intercepting the source is increased up to six-fold. We demonstrate that this "differential strategy" is robust against numerous variations, including order-of-magnitude increases in the repellent release rate. Finally, we leverage existing data to show that E. coli is attracted to fast-diffusing amino acids and repelled by slow-diffusing ones, suggesting it may utilize a differential strategy and providing an explanation for its repulsion from these amino acids. Our results thus illuminate new possibilities in how microbes can integrate signals from multiple gradients to accomplish the difficult chemotactic tasks.

ecology↗

bioRxiv2023

Resource competition can explain simplicity in microbial community assembly

Predicting the composition and diversity of communities is a central goal in ecology. While community assembly is considered hard to predict, laboratory microcosms often follow a simple assembly rule based on the outcome of pairwise competitions. This assembly rule predicts that a species that is excluded by another species in pairwise competition cannot survive in a multispecies community with that species. Despite the empirical success of this bottom-up prediction, its mechanistic origin has remained elusive. In this study, we elucidate how this simple pattern in community assembly can emerge from resource competition. Our geometric analysis of a consumer-resource model shows that trio community assembly is always predictable from pairwise outcomes when one species grows faster than another species on every resource. We also identify all possible trio assembly outcomes under three resources and find that only two outcomes violate the assembly rule. Simulations demonstrate that pairwise competitions accurately predict trio assembly with up to 100 resources and the assembly of larger communities containing up to twelve species. We then further demonstrate accurate quantitative prediction of community composition using harmonic mean of pairwise fractions. Finally, we show that cross-feeding between species does not decrease assembly rule prediction accuracy. Our findings highlight that simple community assembly can emerge even in ecosystems with complex underlying dynamics. SignificanceMultispecies microbial communities play an essential role in the health of ecosystems ranging from the ocean to the human gut. A major challenge in microbial ecology is to understand and predict which species can coexist within a community. While a simple empirical rule utilizing only pairwise outcomes successfully predicts multispecies laboratory communities, its mechanistic origin has remained unexplained. Here, we find that the observed simplicity can emerge from competition for resources. Using a generic consumer-resource model, we demonstrate that community assembly of highly complex ecosystems is nevertheless well predicted by pairwise competitions. Our results argue that community assembly can be surprisingly simple despite the potential complexity associated with competition and crossfeeding of many different resources by many different species.

ecology↗

bioRxiv2023

Biodiversity is enhanced by sequential resource utilization and environmental fluctuations via emergent temporal niches

How natural communities maintain their remarkable biodiversity and which species survive in complex communities are central questions in ecology. Resource competition models successfully explain many phenomena but typically predict only as many species as resources can coexist. Here, we demonstrate that sequential resource utilization, or diauxie, with periodic growth cycles can support many more species than resources. We explore how communities modify their own environments by sequentially depleting resources to form sequences of temporal niches, or intermediately depleted environments. Biodiversity is enhanced when community-driven or environmental fluctuations modulate the resource depletion order and produce different temporal niches on each growth cycle. Community-driven fluctuations under constant environmental conditions are rare, but exploring them illuminates the temporal niche structure that emerges from sequential resource utilization. With environmental fluctuations, we find most communities have more stably coexisting species than resources with survivors accurately predicted by the same temporal niche structure and each following a distinct optimal strategy. Our results thus present a new niche-based approach to understanding highly diverse fluctuating communities.

systems biology↗