The Mucoid Switch in Pseudomonas aeruginosa Represses Quorum Sensing Systems and Leads to Complex Changes to Stationary Phase Virulence Factor Regulation

Abstract

The opportunistic pathogen Pseudomonas aeruginosa chronically infects the airways of Cystic Fibrosis (CF) patients during which it adapts and undergoes clonal expansion within the lung. It commonly acquires inactivating mutations of the anti-sigma factor MucA leading to a mucoid phenotype, caused by excessive production of the extracellular polysaccharide alginate that is associated with a decline in lung function. Alginate production is believed to be the key benefit of mucA mutations to the bacterium in the CF lung. A phenotypic and gene expression characterisation of the stationary phase physiology of mucA22 mutants demonstrated complex and subtle changes in virulence factor production, including cyanide and pyocyanin, that results in their down-regulation upon entry into stationary phase but, (and in contrast to wildtype strains) continued production in prolonged stationary phase. These findings may have consequences for chronic infection if mucoid P. aeruginosa were to continue to make virulence factors under non-growing conditions during infection. These changes resulted in part from a severe down-regulation of both AHL-and AQ (PQS)-dependent quorum sensing systems. In trans expression of the cAMP-dependent transcription factor Vfr restored both quorum sensing defects and virulence factor production in early stationary phase. Our findings have implications for understanding the evolution of P. aeruginosa during CF lung infection and it demonstrates that mucA22 mutation provides a second mechanism, in addition to the commonly occurring lasR mutations, of down-regulating quorum sensing during chronic infection this may provide a selection pressure for the mucoid switch in the CF lung.

Phenotypic characterization of an international Pseudomonas aeruginosa reference panel: strains of cystic fibrosis (CF) origin show less in vivo virulence than non-CF strains

“…Fluctuations in pyocyanin production in a series of 40 LES strains were reported, with overproduction during exacerbations in some CF patient strains and loss of pyocyanin during exacerbations in others (Fothergill et al, 2010). Downregulation of pyocyanin production was associated with a mucoid to non-mucoid switch (Ryall et al, 2014). Consistent with this, the mucoid strain IST 27 produced more pyocyanin relative to the spontaneous non-mucoid variant, IST 27N.…”

A Low-Molecular-Weight Alginate Oligosaccharide Disrupts Pseudomonal Microcolony Formation and Enhances Antibiotic Effectiveness

“…In P. aeruginosa, this adaption occurs with a switch to the mucoid phenotype, characterized by overproduction of high-molecular-mass (Ͼ15-kDa) alginate exopolysaccharide (EPS) (7,8). This switch is accompanied by modification of acyl homoserine lactone (AHL)-and Pseudomonas quinolone signal (PQS)-dependent quorum-sensing (QS) systems (9), with altered production of virulence factors, e.g., pyocyanin and hydrogen cyanide (10). Extracellular alginate affords protection from host innate immune responses, including phagocytosis and neutrophil-derived reactive oxygen species (11).…”

Influence of the alginate production on cell‐to‐cell communication in Pseudomonas aeruginosa PAO1

“…In this study, we show that alginate production alters the signalling response in P. aeruginosa PAO1 mucA22 strain. In a previous study, it was shown that both quinolone signalling and AHL signalling were repressed in the mucoid variant due to the low expression of QS genes (Ryall et al ., ). We further show that the alginate production itself influences the response to quinolone signals but not AHLs.…”

“…An equivalent amount of DMSO was added to control cultures. The pyocyanin assay was performed as described (Ryall et al ., ). The supernatant was collected by centrifugation.…”