SpxA1 and SpxA2 Act Coordinately To Fine-Tune Stress Responses and Virulence in Streptococcus pyogenes

Abstract

SpxA is a unique transcriptional regulator highly conserved among members of the phylum Firmicutes that binds RNA polymerase and can act as an antiactivator. Why some Firmicutes members have two highly similar SpxA paralogs is not understood. Here, we show that the SpxA paralogs of the pathogen Streptococcus pyogenes, SpxA1 and SpxA2, act coordinately to regulate virulence by fine-tuning toxin expression and stress resistance. Construction and analysis of mutants revealed that SpxA1− mutants were defective for growth under aerobic conditions, while SpxA2− mutants had severely attenuated responses to multiple stresses, including thermal and oxidative stresses. SpxA1− mutants had enhanced resistance to the cationic antimicrobial molecule polymyxin B, while SpxA2− mutants were more sensitive. In a murine model of soft tissue infection, a SpxA1− mutant was highly attenuated. In contrast, the highly stress-sensitive SpxA2− mutant was hypervirulent, exhibiting more extensive tissue damage and a greater bacterial burden than the wild-type strain. SpxA1− attenuation was associated with reduced expression of several toxins, including the SpeB cysteine protease. In contrast, SpxA2− hypervirulence correlated with toxin overexpression and could be suppressed to wild-type levels by deletion of speB. These data show that SpxA1 and SpxA2 have opposing roles in virulence and stress resistance, suggesting that they act coordinately to fine-tune toxin expression in response to stress. SpxA2− hypervirulence also shows that stress resistance is not always essential for S. pyogenes pathogenesis in soft tissue.

RocA Has Serotype-Specific Gene Regulatory and Pathogenesis Activities in Serotype M28 Group A Streptococcus

“…Similarly, the stress response genes ciaHR, nrdR, and spxA2 and the arginine deiminase pathway genes arcABCD had significantly increased transcript levels in the ΔrocA M28 mutant strain ( Fig. 4) (44,48,61,74,75). Consistent with the RNA-seq data, the isogenic ΔrocA strain had increased resistance to acidic stress, a condition encountered in purulent lesions (70)(71)(72).…”

“…During infection, GAS cells are exposed to oxidative and acid stress in purulent lesions (70)(71)(72). Among the 41 transcription regulators that are directly or indirectly regulated by RocA in M28 GAS, 4 are implicated in oxidative and acidic stress responses, including the CiaHR twocomponent system, NrdR, and SpxA2 (Table 1) (44,48,61). Additionally, the arcABCD operon had significantly increased transcript levels in the ΔrocA mutant strain ( Fig.…”

Transcriptional regulator SpxA1a controls the resistance of the honey bee pathogen Melissococcus plutonius to the antimicrobial activity of royal jelly

“…SpxA is a unique transcriptional regulator highly conserved among members of the phylum Firmicutes (Port et al, 2017). Spx proteins lack a DNA-binding domain and instead mediate positive or negative transcriptional regulation by interacting with the carboxyl terminal domain of the RNA polymerase α-subunit (α-CTD) (Nakano et al, 2003a).…”

The group A Streptococcus accessory protein RocA: regulatory activity, interacting partners and influence on disease potential

“…The group A Streptococcus (GAS; Streptococcus pyogenes ) causes a range of human diseases, from self‐limiting pharyngitis (aka strep throat) to the often lethal necrotizing fasciitis (aka the flesh‐eating infection) (Cunningham, ). Due to divergent disease manifestations, and significant genome sequence data, GAS has become a model organism to investigate how the virulence and disease potential of a pathogen is influenced by differences in gene content and expression (Sumby et al , ; Olsen et al , ; Hondorp et al , ; Lynskey et al , ; Nasser et al , ; Miller et al , ; Do et al , ; Port et al , ; Kachroo et al , ). Multiple standalone transcriptional regulators (McIver, ), two‐component systems (Vega et al , ), quorum sensing systems (Jimenez and Federle, ) and small regulatory RNAs (Miller et al , ) have been characterized, and together they form an interconnecting web of regulatory networks that influence virulence gene expression (Kreikemeyer et al , ; Sarkar and Sumby, ).…”