The Listeria monocytogenes Hibernation-Promoting Factor Is Required for the Formation of 100S Ribosomes, Optimal Fitness, and Pathogenesis

Abstract

During exposure to certain stresses, bacteria dimerize pairs of 70S ribosomes into translationally silent 100S particles in a process called ribosome hibernation. Although the biological roles of ribosome hibernation are not completely understood, this process appears to represent a conserved and adaptive response that contributes to optimal survival during stress and post-exponential-phase growth. Hibernating ribosomes are formed by the activity of one or more highly conserved proteins; gammaproteobacteria produce two relevant proteins, ribosome modulation factor (RMF) and hibernation promoting factor (HPF), while most Gram-positive bacteria produce a single, longer HPF protein. Here, we report the formation of 100S ribosomes by an HPF homolog in Listeria monocytogenes. L. monocytogenes 100S ribosomes were observed by sucrose density gradient centrifugation of bacterial extracts during mid-logarithmic phase, peaked at the transition to stationary phase, and persisted at lower levels during post-exponential-phase growth. 100S ribosomes were undetectable in bacteria carrying an hpf::Himar1 transposon insertion, indicating that HPF is required for ribosome hibernation in L. monocytogenes. Additionally, epitope-tagged HPF cosedimented with 100S ribosomes, supporting its previously described direct role in 100S formation. We examined hpf mRNA by quantitative PCR (qPCR) and identified several conditions that upregulated its expression, including carbon starvation, heat shock, and exposure to high concentrations of salt or ethanol. Survival of HPF-deficient bacteria was impaired under certain conditions both in vitro and during animal infection, providing evidence for the biological relevance of 100S ribosome formation. Listeria monocytogenes is a Gram-positive, food-borne, facultative intracellular pathogen that infects a broad range of vertebrate hosts (1, 2). The bacterium leads a saprophytic lifestyle in the environment and is commonly found in soil, water, and decaying organic matter. L. monocytogenes most commonly causes disease in elderly, immunocompromised, or pregnant individuals but can pose a general public health risk in cases of severe food contamination. Because of its ability to shift quickly between saprophytic growth in the environment and potentially lethal pathogenesis upon contacting a host, L. monocytogenes has been referred to as a bacterial "Dr. Jekyll and Mr. Hyde" (3). The ability to tolerate or thrive in a variety of unfavorable conditions, including high salt, low pH, and refrigeration temperatures, has made L. monocytogenes a formidable challenge to the food industry (1, 2). Therefore, it is important to understand the set of factors that enable L. monocytogenes to survive so effectively in a wide variety of inhospitable environments. Some of these factors are involved in conserved bacterial stress responses, while others may be specific to Listeria spp. and their close relatives (4).Ribosome hibernation is thought to be an alternative to the classical ribosome recycling pathway, shunting r...

Resuscitation of Pseudomonas aeruginosa from dormancy requires hibernation promoting factor (PA4463) for ribosome preservation

“…Mycobacterium spp. and Listeria monocytogenes, which encode long HPF, require HPF for cell viability maintenance during prolonged incubation and during hypoxic conditions (22,23).…”

Ribosome Hibernation Facilitates Tolerance of Stationary-Phase Bacteria to Aminoglycosides

“…In Escherichia coli, the formation of 100S ribosomes is restricted to stationary phase, where they comprise the majority of the ribosome content (19,20). In contrast, 100S ribosomes formed by long HPF homologs are detected at all phases of growth, with abundance peaking during the transition from logarithmic to stationary-phase growth, where they comprise 50% of the ribosome content (18,21). The function of translationally silent 100S particles during logarithmic growth remains to be elucidated.…”

“…Hibernation-associated factors are important for adaptation to a number of different stresses present during stationary phase, including deprivation of carbon, amino acids, and polyamines, as well as osmotic, heat, and acid stress (23)(24)(25)(26)(27). In addition, our lab recently described ribosome hibernation in L. monocytogenes and highlighted for the first time that 100S ribosomes contribute to bacterial pathogenesis (21). Because 100S ribosomes are induced during nutrient starvation, it has been pro-posed that ribosome hibernation serves to reduce the level of active translation to that commensurate with available nutrients and/or to store and protect ribosomes for use later, when favorable growth conditions return (13,15,23,28).…”

“…Ribosome hibernation is critical for survival during and recovery from a prolonged stationary phase (18,(20)(21)(22)(23). Hibernation-associated factors are important for adaptation to a number of different stresses present during stationary phase, including deprivation of carbon, amino acids, and polyamines, as well as osmotic, heat, and acid stress (23-27).…”

Long-Term Survival of Borrelia burgdorferi Lacking the Hibernation Promotion Factor Homolog in the Unfed Tick Vector

“…Deletion of hpf in E. coli, and of an hpf homolog in Lactococcus lactis, shows that the gene products are involved in ribosome dimerization, and mutants lacking HPF exhibited subtle effects on bacterial survival in E. coli and recovery of L. lactis following starvation (21,32). In addition, deletion of the Listeria monocytogenes hpf homolog eliminated ribosome dimerization and impaired tissue colonization in two mouse infection models (33), while deleting the hpf homolog in Erwinia amylovora, a plant pathogen, rendered this pathogen noninfectious to tobacco leaves and immature pear fruits (34). These studies suggest that HPF plays a role in bacterial survival in vitro and perhaps in vivo.…”