Significance The dormant subpopulations of Pseudomonas aeruginosa biofilms are linked to chronic infections because dormant cells tolerate antibiotic treatment and then repopulate the infections when conditions become favorable. Dormant cells must maintain cellular integrity, including preformed ribosomes, to resuscitate. The small-ribosome–binding proteins, ribosome modulation factor, and hibernation promoting factor (HPF) have evolved to maintain ribosomes in an inactive state. Using both population and single-cell–level studies, we show that HPF provides the primary mechanism used by P. aeruginosa to maintain ribosome integrity during dormancy, and that HPF is required for optimal P. aeruginosa resuscitation from dormancy. Preventing regrowth of the dormant subpopulation by targeting HPF may provide an effective means for eliminating the dormant subpopulations of P. aeruginosa infections.

Pseudomonas aeruginosa is an opportunistic human pathogen that causes severe, life-threatening infections in patients with cystic fibrosis (CF), endocarditis, wounds, or artificial implants. During CF pulmonary infections, P. aeruginosa often encounters environments where the levels of calcium (Ca 2؉ ) are elevated. Previously, we showed that P. aeruginosa responds to externally added Ca 2؉ through enhanced biofilm formation, increased production of several secreted virulence factors, and by developing a transient increase in the intracellular Ca 2؉ level, followed by its removal to the basal submicromolar level. However, the molecular mechanisms responsible for regulating Ca . In addition, a mutation in carP had a pleotropic effect in a Ca 2؉ -dependent manner, altering swarming motility, pyocyanin production, and tobramycin sensitivity. Overall, the results indicate that the two-component system CarSR is responsible for sensing high levels of external Ca 2؉ and responding through its regulatory targets that modulate Ca 2؉ homeostasis, surface-associated motility, and the production of the virulence factor pyocyanin. P seudomonas aeruginosa, a natural inhabitant of soil and water, is able to infect a variety of hosts, including plants and humans. In humans, it causes severe acute and chronic infections by colonizing respiratory and urinary tracts and burned or wounded epithelia, cornea, and muscles (1-3). The versatility of P. aeruginosa pathogenicity is associated with diverse metabolic capabilities, multiple mechanisms of resistance, a large repertoire of virulence factors, and adaptability, due in part to the tightly coordinated regulation of gene expression. A large portion of the P. aeruginosa PAO1 genome, approximately 9.4%, encodes transcriptional regulators (4, 5), including two-component regulators: 89 response regulators, 55 sensor kinases, and 14 sensorresponse regulator hybrids (2). The regulatory targets for most of these regulatory systems are unknown. IMPORTANCE During infectious disease,Calcium plays an important signaling role in both eukaryotic and prokaryotic cells. In prokaryotes, Ca 2ϩ is an essential nutrient, since it is a necessary cofactor for many enzymes. However, Ca 2ϩ can be toxic to cells at high concentrations; therefore, bacteria maintain a low-submicromolar intracellular concentration of Ca 2ϩ (6). P. aeruginosa may encounter environments where

No abstract

Bacteria have traditionally been studied as single-cell organisms. In laboratory settings, aerobic bacteria are usually cultured in aerated flasks, where the cells are considered essentially homogenous. However, in many natural environments, bacteria and other microorganisms grow in mixed communities, often associated with surfaces. Biofilms are comprised of surface-associated microorganisms, their extracellular matrix material, and environmental chemicals that have adsorbed to the bacteria or their matrix material. While this definition of a biofilm is fairly simple, biofilms are complex and dynamic. Our understanding of the activities of individual biofilm cells and whole biofilm systems has developed rapidly, due in part to advances in molecular, analytical, and imaging tools and the miniaturization of tools designed to characterize biofilms at the enzyme level, cellular level, and systems level.

No abstract