Abstract
The facultative intracellular bacterium Legionella pneumophila replicates in environmental amoebae and in lung macrophages, and causes Legionnaires’ disease. Here we show that L. pneumophila reversibly forms replicating and nonreplicating subpopulations of similar size within amoebae. The nonreplicating bacteria are viable and metabolically active, display increased antibiotic tolerance and a distinct proteome, and show high virulence as well as the capacity to form a degradation-resistant compartment. Upon infection of naïve or interferon-γ-activated macrophages, the nonreplicating subpopulation comprises ca. 10% or 50%, respectively, of the total intracellular bacteria; hence, the nonreplicating subpopulation is of similar size in amoebae and activated macrophages. The numbers of nonreplicating bacteria within amoebae are reduced in the absence of the autoinducer synthase LqsA or other components of the Lqs quorum-sensing system. Our results indicate that virulent, antibiotic-tolerant subpopulations of L. pneumophila are formed during infection of evolutionarily distant phagocytes, in a process controlled by the Lqs system.
Highlights
The facultative intracellular bacterium Legionella pneumophila replicates in environmental amoebae and in lung macrophages, and causes Legionnaires’ disease
To explore whether a clonal population of L. pneumophila shows phenotypic heterogeneity within host cells, we investigated growth rate heterogeneity of single bacteria in their natural host, the free-living ameba Acanthamoeba castellanii
As a readout for the growth rate, we adapted for L. pneumophila the Timerbac system, a stable fluorescent reporter that slowly maturates from a green to a red fluorescent protein[2]
Summary
The facultative intracellular bacterium Legionella pneumophila replicates in environmental amoebae and in lung macrophages, and causes Legionnaires’ disease. We show that L. pneumophila reversibly forms replicating and nonreplicating subpopulations of similar size within amoebae. 10% or 50%, respectively, of the total intracellular bacteria; the nonreplicating subpopulation is of similar size in amoebae and activated macrophages. The numbers of nonreplicating bacteria within amoebae are reduced in the absence of the autoinducer synthase LqsA or other components of the Lqs quorum-sensing system. Our results indicate that virulent, antibiotictolerant subpopulations of L. pneumophila are formed during infection of evolutionarily distant phagocytes, in a process controlled by the Lqs system. The nonreplicating subpopulation is of similar size in amoebae and interferon-γ-activated macrophages, and is controlled by the Lqs system
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