Role of starvation survival response mechanisms on ribosome integrity, antibiotic tolerances, and virulence of Pseudomonas aeruginosa biofilms.

Bacterial biofilms contain physiologically diverse subpopulations of cells, including cells that are nutrient stressed or dormant. We determined how two dormancy pathways, ribosome hibernation and the stringent response, contribute to the survival and antibiotic tolerance of Pseudomonas aeruginosa biofilms. Analyses of whole biofilms and single cells showed that these pathways have differing effects on biofilm cell physiology. Ribosome hibernation, mediated by hibernation promoting factor (HPF), is essential for optimal survival and resuscitation of starved biofilm cells. In the absence of HPF, starved cells progressively lose ribosome integrity. However, loss of HPF does not increase the sensitivity of P. aeruginosa biofilm cells to ciprofloxacin or tobramycin. In contrast, the stringent response, mediated by RelA and SpoT, is not required for viability or ribosome integrity in starved biofilm cells, but does affect biofilm antibiotic tolerance. In a plant model of biofilm infection, disruption of either ribosome hibernation or the stringent response reduced bacterial virulence. The results show that ribosome hibernation preserves ribosomal integrity necessary for recovery from starvation and for pathogenesis, while the stringent response is required for growth arrest, antibiotic tolerance, and pathogenesis. These two ribosome-mediated pathways play distinct yet complementary roles in regulating dormancy and persistence of P. aeruginosa biofilms.