Tunable effect of divalent cations on tendril patterning during swarming motility of Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa’s remarkable adaptability makes it valuable for bioremediation but problematic in healthcare settings, highlighting the need for context-dependent regulation of its colonization. Current research on bacterial swarming is limited by the lack of a minimal media that allows systematic study of factors affecting tendril patterning. Using a simplified swarming media (SM), we demonstrate that divalent cations tune P. aeruginosa’s colonization by modulating cell density, surface charges, and rhamnolipid production without altering flagellar numbers. At colony edges, divalent cations stimulate cell growth and trigger quorum signalling while reducing surface charges. This creates a dynamic environment where bacterial cells with reduced surface charges and active flagella are suspended in an aqueous-rhamnolipid solution experience the Marangoni effect. This leads to non-uniform cell distribution within the colony, concentrating cells at tendril tips where fresh divalent cations are available. This localized concentration amplifies cell density and rhamnolipid expression through a positive feedback loop, promoting the formation of additional tendrils rather than increasing tendril thickness. Overall, our findings reveal how a single environmental parameter − divalent cation concentration − alone can effectively tune bacterial colonization behaviour. This mechanistic insight could enable the development of targeted strategies offering potential applications in both bioremediation and medical contexts, though further research is needed to validate these applications under field conditions.