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This study investigates sibling inhibition in Pseudomonas aeruginosa, a phenomenon in which genetically identical bacterial colonies growing in soft agar hydrogels avoid each other and form sharp boundary lines. Using quantitative density measurements combined with a minimal biophysical model, the researchers demonstrate that this separation is not caused by gel compression, lethal inhibition, or quorum sensing-based communication. Instead, the effect is driven by localized nutrient depletion through a dynamic feedback loop between bacterial growth and motility, a conclusion supported by the model's ability to reproduce the observed dependence of inhibition strength on initial nutrient concentration.
Why it matters
Understanding the physical and nutritional mechanisms behind bacterial spatial organization has direct implications for predicting microbial behavior in clinical contexts such as tissue infections, as well as in environmental and engineered microbiome settings. This framework could inform the design of strategies to manipulate bacterial colony dynamics in soils, biomedical applications, and synthetic microbiome engineering.
arXiv:2605.13927v1 Announce Type: new
Abstract: The striking variety of macroscopic morphologies displayed by bacterial colonies depends on microscopic environmental and behavioural details in a manner that is currently not well understood. A surprising example is sibling inhibition, whereby isogenic bacterial colonies spreading in soft agar hydrogels tend to avoid each other and form sharp demarcation lines when growing nearby. Here we investigate this effect with the common pathogen textit{Pseudomonas aeruginosa}, by combining quantitative density measurements with a minimal biophysical model. Our results show that the phenomenon does not depend on gel compression, lethal inhibition or quorum sensing-dependent cell communication. Instead, colony separation is driven by localised nutrient depletion through a dynamic feedback between growth and motility. The model, which is calibrated using experimental data, captures key observations including the dependence of inhibition strength on the initial nutrient concentration. This work establishes nutrient availability and non-lethal motility inhibition as central factors underlying sibling inhibition, providing a generalisable framework for microbial spatial dynamics with implications for understanding bacterial interactions in tissues, soils and engineered microbiomes.