Quorum sensing controls persistence, resuscitation, and virulence ofLegionellasubpopulations in biofilms

The water-borne bacteriumLegionella pneumophilais the causative agent of Legionnaires' disease. In the environment, the opportunistic pathogen colonizes different niches, including free-living protozoa and biofilms. The physiological state(s) of sessileLegionellain biofilms and their functional consequences are not well understood. Using single-cell techniques and fluorescent growth rate probes as well as promoter reporters, we show here that sessileL. pneumophilaexhibits phenotypic heterogeneity and adopts growing and nongrowing (dormant) states in biofilms and microcolonies. Phenotypic heterogeneity is controlled by theLegionellaquorum sensing (Lqs) system, the transcription factor LvbR, and the temperature. The Lqs system and LvbR determine the ratio between growing and nongrowing sessile subpopulations, as well as the frequency of growth resumption (resuscitation) and microcolony formation of individual bacteria. NongrowingL. pneumophilacells are metabolically active, express virulence genes and show tolerance toward antibiotics. Therefore, these sessile nongrowers are persisters. Taken together, the Lqs system, LvbR and the temperature control the phenotypic heterogeneity of sessileL. pneumophila, and these factors regulate the formation of a distinct subpopulation of nongrowing, antibiotic tolerant, virulent persisters. Hence, the biofilm niche ofL. pneumophilahas a profound impact on the ecology and virulence of this opportunistic pathogen.

Automated summary

The study reveals that sessile L. pneumophila in biofilms exhibit phenotypic heterogeneity, adopting growing and nongrowing states, which are controlled by the Legionella quorum sensing system, the transcription factor LvbR, and temperature. This diversity plays a key role in the formation of antibiotic-tolerant, virulent persisters in the biofilm niche, impacting the ecology and virulence of this opportunistic pathogen.