Distinct transcriptome and traits of freshly dispersed Pseudomonas aeruginosa cells

Bacteria assume two distinct lifestyles: the planktonic and biofilm modes of growth. Additionally, dispersion has emerged as a third phenotype, accompanied by the distinct phenotypes and the unique expression of >600 genes. Here, we asked whether the distinct phenotype of dispersed cells is already apparent within minutes of egressing from the biofilm. We used RNA-seq to show that the physiology of freshly dispersed cells from Pseudomonas aeruginosa biofilms is highly different from those of planktonic and biofilm cells, apparent by dispersed cells uniquely expressing 194 genes. Unique and differentially expressed genes relative to planktonic or biofilm cells include genes associated with type IV pili, pyoverdine, type III and type VI secretion systems, and antibiotic resistance that are downregulated in dispersed cells, whereas the transcript abundance of genes involved in swimming motility, Hxc type II secretion system and various other virulence factors, and metabolic and energy-generating pathways are increased, indicative of dispersion coinciding with an awakening and re-energizing of dispersed cells, and a switch in virulence, further apparent by freshly dispersed cells significantly subverting engulfment by macrophages. The findings suggest that dispersed cells display a distinct phenotype within minutes of egressing from the biofilm, with freshly dispersed cells already capable of efficiently evading phagocytosis.

Dispersion is considered a transitionary phenotype, enabling bacteria to switch between the communal, biofilm lifestyle, where cells share resources and are protected from harmful conditions to the planktonic state. Here, we demonstrate that within minutes of leaving the biofilm, dispersed cells express genes and display phenotypic traits that are distinct from biofilms and planktonic cells. Our findings suggest that dispersed cells quickly adapt to a less structured and protected but more nutrient-rich environment, with this trade-off in environment coinciding with an awakening and a switch in virulence, specifically a switch from directly intoxicating host cells and potential competitors toward more broadly active virulence factors and strategies of evasion. To our knowledge, this is the first report of dispersed cells' distinct (trade-off) phenotype and their enhanced resilience so soon after egressing from the biofilm.