NAD+ pool depletion as a signal for the Rex regulon involved in Streptococcus agalactiae virulence.

Thierry Franza,Philippe Gaudu,Mikael C Bauer,Claes Von Wachenfeldt,Saravanamuthu Thiyagarajan,Aurelie Derré-Bobillot,Derek T Logan,Philippe Glaser,Matthew J Sullivan,Violette Da Cunha,Annika Rogstam,Kelvin G K Goh,Glen C Ulett

doi:10.1371/journal.ppat.1009791

Abstract

In many Gram-positive bacteria, the redox-sensing transcriptional repressor Rex controls central carbon and energy metabolism by sensing the intra cellular balance between the reduced and oxidized forms of nicotinamide adenine dinucleotide; the NADH/NAD+ ratio. Here, we report high-resolution crystal structures and characterization of a Rex ortholog (Gbs1167) in the opportunistic pathogen, Streptococcus agalactiae, also known as group B streptococcus (GBS). We present structures of Rex bound to NAD+ and to a DNA operator which are the first structures of a Rex-family member from a pathogenic bacterium. The structures reveal the molecular basis of DNA binding and the conformation alterations between the free NAD+ complex and DNA-bound form of Rex. Transcriptomic analysis revealed that GBS Rex controls not only central metabolism, but also expression of the monocistronic rex gene as well as virulence gene expression. Rex enhances GBS virulence after disseminated infection in mice. Mechanistically, NAD+ stabilizes Rex as a repressor in the absence of NADH. However, GBS Rex is unique compared to Rex regulators previously characterized because of its sensing mechanism: we show that it primarily responds to NAD+ levels (or growth rate) rather than to the NADH/NAD+ ratio. These results indicate that Rex plays a key role in GBS pathogenicity by modulating virulence factor gene expression and carbon metabolism to harvest nutrients from the host.

Highlights

Streptococcus agalactiae, or group B streptococcus (GBS), is a Gram-positive commensal bacterium that asymptomatically colonizes the human gastrointestinal tract and the vaginal flora of 10 to 30% of healthy women
To further understand how Rex operates in Gram-positive bacteria, we investigated the structure, function and role of this regulator in the serotype III strain NEM316 of GBS isolated from a fatal case of septicaemia [12]
A total of 35 genes were identified as highly differentially expressed as a result of rex deletion (>5-fold change, p

Summary

Introduction

Streptococcus agalactiae, or group B streptococcus (GBS), is a Gram-positive commensal bacterium that asymptomatically colonizes the human gastrointestinal tract and the vaginal flora of 10 to 30% of healthy women. In a sub-population of humans, mainly in newborns or immunocompromised elderly individuals, GBS can become an opportunistic pathogen causing diverse pathologies from meningitis to systemic infections [1,2,3]. GBS can undergo fermentation or aerobic respiration. Endogenous synthesis pathways for haem and DHNA are absent in GBS [12]. These molecules allow activation of a respiratory chain, which is ended by a high-oxygen-affinity cytochrome bd terminal oxidase, CydAB. Respiratory metabolism confers many advantages to GBS, including higher biomass yield, robust senescence in vitro and enhanced virulence in a systemic infection model in mice, indicating its role in GBS pathogenicity [11,13,14]

Methods

Results

Conclusion