Rgg-Shp regulators are important for pneumococcal colonization and invasion through their effect on mannose utilization and capsule synthesis

Xiangyun Zhi,Sulman Shafeeq,Iman Tajer Abdullah,Ozcan Gazioglu,Peter W Andrew,Iman Tajer Abdullah,Oscar P Kuipers,Irfan Manzoor,Hasan Yesilkaya,N Luisa Hiller

doi:10.1038/s41598-018-24910-1

Abstract

Microbes communicate with each other by using quorum sensing (QS) systems and modulate their collective ‘behavior’ for in-host colonization and virulence, biofilm formation, and environmental adaptation. The recent increase in genome data availability reveals the presence of several putative QS sensing circuits in microbial pathogens, but many of these have not been functionally characterized yet, despite their possible utility as drug targets. To increase the repertoire of functionally characterized QS systems in bacteria, we studied Rgg144/Shp144 and Rgg939/Shp939, two putative QS systems in the important human pathogen Streptococcus pneumoniae. We find that both of these QS circuits are induced by short hydrophobic peptides (Shp) upon sensing sugars found in the respiratory tract, such as galactose and mannose. Microarray analyses using cultures grown on mannose and galactose revealed that the expression of a large number of genes is controlled by these QS systems, especially those encoding for essential physiological functions and virulence-related genes such as the capsular locus. Moreover, the array data revealed evidence for cross-talk between these systems. Finally, these Rgg systems play a key role in colonization and virulence, as deletion mutants of these QS systems are attenuated in the mouse models of colonization and pneumonia.

Highlights

During colonization and invasion of human tissues Streptococcus pneumoniae, which causes bacterial pneumonia, meningitis, and septicemia, will encounter a wide range of differing physical and nutritional environments[1,2,3,4]
We studied the role of the Gly-Gly virulence peptide 1 (VP1) in the chinchilla model of middle ear infection by pneumococci, and demonstrated that vp[1] is regulated by a Rgg/SHP quorum sensing (QS) system[9]
The pneumococcal set includes genomes used in the first large-scale pneumococcal pangenome study[31], genomes from PCV-7 immunized children[32], as well as genomes from non-encapsulated strains that make up a distinct phyletic group within the pneumococcus[33,35,36,42]. Together these strains reflect a large variety of multilocus sequence types (MLSTs) and serotypes, as well as strains isolated from different disease states and geographic locations

Summary

Introduction

During colonization and invasion of human tissues Streptococcus pneumoniae (the pneumococcus), which causes bacterial pneumonia, meningitis, and septicemia, will encounter a wide range of differing physical and nutritional environments[1,2,3,4]. Rgg proteins ( known as Gad or Mut) are a conserved family of stand-alone transcriptional regulators characterised by an N-terminal helix-turn-helix motif (HTH), which binds to the promoter of Rgg-regulated genes, and a conserved C-terminal regulatory domain rich in alpha-helices[6,16] They are widely present in a subset of low-G + C Gram-positive bacteria, including Streptococcus, Listeria and Lactobacillus[6]. Studies in other streptococci have shown that Rggs exert control over a wide range of physiological events, including oxidative stress response, non-glucose sugar metabolism, bacteriocin production, biofilm formation, quorum sensing, and virulence[8,11,17] Knowledge of their contribution to S. pneumoniae biology is sparse and requires further investigation[9,18]. Our characterization of the Rgg regulons demonstrates evidence of cross talk between these Rgg/Shp systems and highlights both common and specific components in the Rgg regulons

Methods

Results

Conclusion