Bacteria differently deploy type-IV pili on surfaces to adapt to nutrient availability

Abstract

The structure of bacterial biofilms depends on environmental conditions, such as availability of nutrients, during biofilm formation. In turn, variations in biofilm structure in part reflect differences in bacterial motility during early biofilm formation. Pseudomonas aeruginosa deprived of nutrients remain dispersed on a surface, whereas cells supplemented with additional nutrients cluster and form microcolonies. At the single-cell scale, how bacteria modify their motility to favour distinct life cycle outcomes remains poorly understood. High-throughput algorithms were used to track thousands of P. aeruginosa moving using type-IV pili (TFP) on surfaces in varying nutrient conditions and hence identify four distinct motility types. A minimal stochastic model was used to reproduce the TFP-driven motility types. We report that P. aeruginosa cells differently deploy TFP to alter the distribution of motility types under different nutrient conditions. Bacteria preferentially crawl unidirectionally under nutrient-limited conditions, but preferentially stall under nutrient-supplemented conditions. Motility types correlate with subcellular localisation of FimX, a protein required for TFP assembly and implicated in environmental response. The subcellular distribution of FimX is asymmetric for unidirectional crawling, consistent with TFP assembled primarily at the leading pole, whereas for non-translational types FimX expression is symmetric or non-existent. These results are consistent with a minimal stochastic model that reproduces the motility types from the subcellular average concentration and asymmetry of FimX. These findings reveal that P. aeruginosa deploy TFP symmetrically or asymmetrically to modulate motility behaviours in different nutrient conditions and thereby form biofilms only where nutrients are sufficient, which greatly enhances their competitive capacity in diverse environments.

Microenvironmental Niches and Sanctuaries: A Route to Acquired Resistance

“…In particular, it has been experimentally shown that the emergence of bacterial antibiotic resistance was accelerated in heterogeneous microenvironments [66]. Further, various strains of bacteria were shown to possess the capability to actively form niches to adapt to different environments, such as changes in nutrient availability [45]. It is also worth noting that the concept of persister cells was first described in the context of bacterial infections in which a small number of antibiotic-resistant mutants survived in a dormant non-dividing state [4,36].…”

Modelling bacterial twitching in fluid flows: a CFD-DEM approach

“…Bacterial motility would be affected by the number of pili and how those pili distribute at the bacteria poles 2,17 . Therefore, the present model is employed to understand how the number of pili and the distribution angle ( α ) influence twitching characteristics.…”

“…Twitching motility could depend on many factors including surface properties, pili arrangement on bacterial surface, and environmental conditions such as oxygen concentration and fluid flow rate 16 . For example, when pili emanate only at the poles of bacteria (e.g., Pseudomonas aeruginosa ), the bacteria will have persistent motion 17,18 . But, if pili are all around the cell body (e.g., Neisseria gonorrhoeae ), the bacteria will have trapped or diffusive motion due to the tug of war mechanism 19,20 .…”

“…However, when the surface has micro-scale grooves, bacteria may display persistent twitching along grooves because cells can be guided by the groove walls 2,23 . Bacteria can also differently deploy pili 17 and change pili retraction speed 24 to adapt to nutrient availability. In fluid flow environments, rod-shaped bacteria tend to twitch against the flow because the fluid flow tends to align the bacteria along the flow direction while they are anchored to the tethering points, and then the fluid drag causes bacteria to flip around the anchoring point and twitch upstream (see Figure 1) 25-27 .…”

Toward plasmonic monitoring of surface effects on bacterial quorum-sensing

“…The next stages involve the clumping of cells into microcolonies and growth into a biofilm structure, which can be flat or mushroom-like (Figure 1). The shape of the colony is influenced by the growth and rearrangement of cells through pili-mediated gliding, depending on the available nutrients [5,6]. In the final stage of biofilm growth some motile cells are shed from the biofilm, where they are then able to colonize other surfaces in a new location.…”