Bacteriophage infection reveals pre-emptive cooperative dormancy in stationary phase Escherichia coli

Escherichia coli cultures entering their stationary phase (SP) undergo significant physiological changes to enable survival when the medium's resources are depleted. While it was previously thought that these stress responses were triggered by individual cells reacting to environmental cues like starvation or toxic metabolites, a recent study suggests that pre-emptive cooperative dormancy may be at play.

Escherichia coli phage DH23 can infect and replicate within SP cultures of E. coli MG1655, even though most bacteriophages are rendered ineffective in such conditions. The researchers found that phage replication was possible until 11 hours post-inoculation, but then abruptly dropped off at 13 hours, marking the onset of deeper dormancy during SP.

This middle-SP dormancy (MSPD) appeared to be mediated by intercellular communication through larger than 100 kDa signal particles (MSP) containing both RNA and DNA. These MSP particles inactivate RNAse or DNAse, allowing phage growth in 14-hour-old cultures and reducing the tolerance of these cultures to kanamycin.

Furthermore, the treatment with RNAse or DNAse made 24-hour culture spent media suitable for additional cell growth, and cultures initiated in fresh LB supplemented with RNAse reached an OD600 value about 1.5 times higher compared to untreated controls. This indicates that MSP signaling influences cell physiology well before MSPD onset, enabling the population to cease growth pre-emptively. This adaptive behavior saves about one-third of medium resources, ensuring the population's viability during the stationary phase.