Modeling downstream impact of a quorum sensing system of Pseudomonas aeruginosa in colony spreading

A single bacterial colony typically consists of two or more individual cells. To further growth, the cells within the colony need to coordinate through Quorum Sensing (QS), which serves as a communication mechanism between cells. The Quorum Sensing signalling system in Pseudomonas aeruginosa is known to involve multiple control components, notably the las and rhl systems. The las system controls the rhl system in a hierarchical signalling cascade, and the rhl system regulates certain gene expressions, including the rhlA and rhlB genes. Transcription of rhlA and rhlB results in the production of the enzyme rhamnosyltransferase, which leads to the biosurfactant production identified as rhamnolipids. In this paper, we investigate how the las system controls the rhl system to influence rhamnolipids production. We illustrate how the pulsed production of signal molecules in the las system affects the rhl system, leading to an increase in rhamnolipids concentration. Rhamnolipids play a crucial role in bacterial spreading. We employ a simple symmetric diffusion model to simulate colony spreading and demonstrate how bacteria spread from the centre of the colony. Our findings shed light on the interaction between the las and rhl systems, which may enable cells to trigger rhamnolipids production at the edge of the bacterial colony.