Bisesi, A. T. | Search bioRxiv

bioRxiv2026

Cross-feeding reshapes interactions between antibiotic stressors through metabolic feedbacks

Stressors can combine to inhibit organismal growth or function more (synergy) or less (antagonism) strongly than expected from their individual effects, yet whether these interactions are intrinsic properties of cells or stressors, or emergent consequences of ecological interactions remains unclear. Antibiotic combinations provide a tractable model for studying stressor interactions, but have been characterized largely in bacterial monocultures. Here, we compared antibiotic stressor interactions in Escherichia coli growth in monoculture versus when cross-feeding with Salmonella enterica. Across 36 antibiotic pairs, cross-feeding frequently shifts interactions toward antagonism and away from synergy. In the sulfamethoxazole-trimethoprim pair, dual treatment increases carbon excretion by E. coli, promoting partner growth and attenuating stressor synergy through reciprocal metabolic feedback. Perturbing partner metabolite usage restores monoculture-like interaction outcomes across multiple drug pairs. Together, our results demonstrate that stressor interactions in microorganisms can emerge from ecological feedbacks mediated by metabolic excretion.

microbiology↗

bioRxiv2023

Bacteriophage diet breadth is impacted by interactions between bacteria

Predators play a central role in shaping community structure, function, and stability. The degree to which bacteriophage predators (viruses that infect bacteria) evolve to be specialists with a single bacterial prey species versus generalists able to consume multiple types of prey has implications for their effect on microbial communities. The presence and abundance of multiple bacterial prey types can alter selection for phage generalists, but less is known about how interactions between prey shapes diet breadth in microbial systems. Using a phenomenological mathematical model of phage and bacterial populations, we find that the dominant phage strategy depends on prey ecology. Given a fitness cost for generalism, generalist predators maintain an advantage when prey species compete, while specialists dominate when prey are obligately engaged in cross-feeding interactions. We test these predictions in a synthetic microbial community with interacting strains of Escherichia coli and Salmonella enterica by competing a generalist T5-like phage able to infect both prey against P22vir, an S. enterica-specific phage. Our experimental data conform to our modeling expectations when prey are competing or obligately mutualistic, although our results suggest that the in vitro cost of generalism is caused by a biological mechanism not represented in our model. Our work demonstrates that interactions between bacteria play a role in shaping ecological selection on diet breadth in bacteriophage and emphasizes the diversity of ways in which fitness trade-offs can manifest.

ecology↗