Regulation Of Pneumococcal Epigenetic And Colony Phases By Two-component Regulatory Systems

Streptococcus pneumoniae is a Gram-positive human pathogen,which occasionally causes infectious diseases including otitis media,pneumonia,sepsis and meningitis.This bacterium is well known for phase variation between opaque(O)and transparent(T)colonies within clonal populations.While the O variant is specialized in invasive infection(with a thicker capsule and higher resistance to host clearance),the T counterpart possesses a relatively thinner capsule and thereby higher airway adherence and colonization.Our previous study found that phase variation is caused by reversible switches of the “opaque ON-or-OFF” methylomes of pneumococcal genome,which is dominantly driven by the Psr A-catalyzed inversions of the DNA methyltransferase hsd S genes in the cod locus,a type I restriction-modification system(RM).This study revealed that the switching orientation between O and T variants is regulated by five transcriptional response regulators(rr)of the two-component signal transduction systems(TCSs).The mutants of rr06,rr08,rr09,rr11 and rr14 produced significantly fewer O and more T colonies.Further mutagenesis revealed that RR06,RR08,RR09 and RR11 enrich the O variant by modulating the directions of the Psr A-catalyzed inversion reactions.In contrast,the impact of RR14(Rit R)on phase variation is independent of Psr A-catalyzed DNA inversions.Consistently,SMRT sequencing uncovered significantly diminished “opaque ON” methylome in the mutants of rr06,rr08,rr09 and rr11 but not that of rr14.Lastly,the phosphorylated form of RR11 was shown to activate the transcription of com W and two sugar utilization systems that are necessary for maintenance of the “opaque ON”genotype and phenotype.Since two-component systems represent a fundamental mechanism for bacterial sensing and responding to environmental conditions,this work has uncovered a new level of molecular sophistication and complexity in bacterial finetuning of its biological activities and behaviors by linking the environmental sensing systems to the epigenetic switching machinery.Together,this work has thus revealed multiple novel mechanisms that balance pneumococcal epigenetic status and physiology,which is a breakthrough understanding of pneumococcal pathogenesis.