Transcriptional profiling of Pseudomonas aeruginosa biofilm life cycle stages reveals dispersal-specific biomarkers

Bacteria exhibit two lifestyles: planktonic free-floating individual cells or sessile multicellular aggregates known as biofilms. The biofilm lifecycle is characterised by three distinct stages: attachment, maturation and dispersal. Specific signals govern each stage triggering responses that spatially and temporally regulate bacterial attachment to a surface, synthesis of extracellular matrix components and their subsequent degradation. Characterising these signals is therefore a valuable approach to develop novel antibiofilm therapies. Here, we used the model biofilm-forming bacterium Pseudomonas aeruginosa PAO1 to characterise the transcriptional profiles of each stage of the biofilm life cycle: attachment, biofilm maturation and spontaneous dispersal. We report that surface attachment was accompanied by the upregulation of genes comprising the mechanosensor Pil-Chp, whereas biofilm maturation characterised with the upregulation of genes involved in Pel polysaccharide synthesis, siaD and PA4396 diguanylate cyclases as well as pipA, fimX and PA5442. In contrast, dispersing cells upregulated genes responsible for alginate, rhamnolipid, and extracellular nucleases (eddA, eddB) biosynthesis, as well as the transcriptional regulator of dispersal amrZ. Additionally, genes encoding the quorum sensing dispersal molecule cis-2-decenoic acid (dspS and dspI), canonical phosphodiesterases (nbdA and rbdA) and eleven other c-di-GMP-related enzymes were also upregulated during dispersal. Our comprehensive analysis of transcriptional profiles associated with different biofilm stages allowed us to define a subset of fourteen genes as biomarkers of biofilm dispersal. Our study therefore provides benchmarking stage-specific transcriptional profiles for P. aeruginosa biofilms in closed culture systems, which led to the identification of a dispersal fingerprint marking the onset of dispersal.