Quorum sensing elicits functionally distinct subpopulations of infectious Legionella

Clonal bacterial populations respond to unfavorable conditions with growth arrest and 20 persistence. Here we show that quorum sensing (QS) determines functionally distinct subpopulations of non-growing, virulent Legionella. QS increases the fraction of bacteria re- initiating growth in microcolonies, while it restricts the ratio of bacteria resuming growth in free- living protozoan predators. QS continues to govern the population heterogeneity throughout growth. Intracellular non-growers and growing bacteria are characterized by distinct proteomes 25 reflecting different stress and drug tolerance as well as alternative metabolic pathways. Strikingly, individual intracellular non-growers are persisters, which endure host killing mechanisms, produce virulence factors, form a replication-permissive compartment, and are highly infectious. Thus, QS underlies a bet-hedging strategy of non-growing intracellular bacterial pathogens to resume growth and to fine-tune virulence.