Characterizing the Molecular Mechanisms Involved in the Formation of Multidrug-tolerant Persister Cells in Streptococcus mutans

Bacterial populations contain a small fraction of specialized dormant cells known as persisters that ensure survival from killing by all antibiotics currently in use. These multidrug-tolerant persisters are phenotypic variants that withstand cell death from antibiotics due to inactive cellular processes that most conventional antibiotics target, and are capable of reverting to normal growing cells upon the removal of antibiotics. Thus, persisters are a major contributor in resiliency of chronic microbial infections towards antibiotic therapy. Streptococcus mutans utilizes quorum-sensing for coordinating and regulating bacterial behaviors and adaptive responses at a population-wide level. Previous work has shown that this cariogenic pathogen utilizes its CSP-ComDE quorum-sensing system to direct its stress response for survival. Our objectives were to investigate the nonheritable persister phenotype in S. mutans, and to identify the molecular mechanisms by which it forms these multidrug-tolerant persisters. Persister formation in S. mutans was found to be regulated by multiple mechanisms, including two toxin-antitoxin systems, genes involved in transcription/replication, sugar metabolism, cell wall synthesis, and energy metabolism. Furthermore, we identified that the inducible CSP ‘alarmone’, the peptide pheromone responsible for communicating stress and triggering adaptive responses in the population, is important for the induction of persister formation. We demonstrated that this inducible mechanism is regulated by a CSP-inducible gene encoding a transcriptional repressor that is responsible for regulating DNA damage tolerance and identified novel persister genes that contribute to the formation of quorum-sensing-induced persister cells.Ph.D