A Streptococcus Quorum Sensing System Enables Suppression of Innate Immunity

Abstract

Some bacterial pathogens utilize cell-cell communication systems, such as quorum sensing (QS), to coordinate genetic programs during host colonization and infection. The human-restricted pathosymbiont Streptococcus pyogenes (group A streptococcus [GAS]) uses the Rgg2/Rgg3 QS system to modify the bacterial surface, enabling biofilm formation and lysozyme resistance. Here, we demonstrate that innate immune cell responses to GAS are substantially altered by the QS status of the bacteria. We found that macrophage activation, stimulated by multiple agonists and assessed by cytokine production and NF-κB activity, was substantially suppressed upon interaction with QS-active GAS but not QS-inactive bacteria. Neither macrophage viability nor bacterial adherence, internalization, or survival were altered by the QS activation status, yet tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), and interferon beta (IFN-β) levels and NF-κB reporter activity were drastically lower following infection with QS-active GAS. Suppression required contact between viable bacteria and macrophages. A QS-regulated biosynthetic gene cluster (BGC) in the GAS genome, encoding several putative enzymes, was also required for macrophage modulation. Our findings suggest a model wherein upon contact with macrophages, QS-active GAS produce a BGC-derived factor capable of suppressing inflammatory responses. The suppressive capability of QS-active GAS is abolished after treatment with a specific QS inhibitor. These observations suggest that interfering with the ability of bacteria to collaborate via QS can serve as a strategy to counteract microbial efforts to manipulate host defenses. IMPORTANCE Streptococcus pyogenes is restricted to human hosts and commonly causes superficial diseases such as pharyngitis; it can also cause severe and deadly manifestations including necrotizing skin disease or severe postinfectious sequelae like rheumatic heart disease. Understanding the complex mechanisms used by this pathogen to manipulate host defenses could aid in developing new therapeutics to treat infections. Here, we examine the impact of a bacterial cell-cell communication system, which is highly conserved across S. pyogenes, on host innate immune responses. We find that S. pyogenes uses this system to suppress macrophage proinflammatory cytokine responses in vitro. Interference with this communication system could serve as a strategy to disarm bacteria and maintain an effective immune response.

The proteomic and transcriptomic landscapes altered by Rgg2/3 activity in Streptococcus pyogenes

“…al , 2022, submitted). stcA is associated with enhanced lysozyme resistance and biofilm formation, whereas spy49_0450-0460 is required for QS-induced immune suppression (5, 9, 14).…”

“…Genetic programs that regulate virulence attributes of GAS are responsive to the microorganism's environment, and its metabolic status, through intercellular signaling networks. Quorum sensing (QS), a form of intercellular communication, is used by GAS to regulate gene expression in response to molecular signals produced by bacteria (5)(6)(7)(8)(9)(10)(11). QS activity is often coupled to the status of the environment, where characteristics such as nutrient availability or pH can impact expression or action of QS-centric genes.…”

“…GAS possesses four Rgg proteins, RopB (Rgg1), Rgg2 and Rgg3 (Rgg2/3), and ComR (Rgg4) (13). Several studies have documented their roles in virulence, biofilm formation, and lysozyme resistance (5,6,8,9,11,14,15). Rgg2 and Rgg3 are allosteric regulators of transcription that respond indiscriminately to the short hydrophobic peptides SHP2 and SHP3.…”

Quorum sensing regulation of a major facilitator superfamily transporter affects multiple streptococcal virulence factors

“…A PHYRE search using the GAS amino acid sequence revealed structural matches to other MFS proteins including the human iron export protein ferroportin-1, the bacilysin/siderophore transporter BacE, and the lipoteichoic acid flippase LtaA 24 . The former two hits are potentially interesting given that we previously observed that Rgg2/3 signaling is induced under conditions of iron limitation 3 and spy49_0460 is located at the end of a BGC, and the latter is interesting due to the possibility that the BCG produces a factor that alters the GAS cell surface and its subsequent interactions with macrophages 6 . However, we have not found a role for the BGC in iron uptake or a role for Spy49_0460 specifically in macrophage suppression to date.…”

“…Four types of quorum-sensing systems have been described for GAS: Sil, lantibiotic systems, LuxS/AI-2, and regulator gene of glucosyltransferase (Rgg) systems 2 . Of the latter, GAS possess four Rgg-type transcription factors which interact with small oligopeptide pheromones to control three discrete regulons: RopB (Rgg1) mediates expression of the SpeB cysteine protease, a well-characterized virulence factor; ComR (Rgg4) is implicated in natural competence; and Rgg2 and Rgg3 together regulate genes linked to cell aggregation, biofilm formation, lysozyme resistance, nasopharyngeal colonization, pharyngitis and macrophage immunosuppression [3][4][5][6][7][8][9][10] . The Rgg2/3 system is unique in that the two homologous regulators recognize the same pheromones (short hydrophobic peptides 2 and 3; SHP2 and SHP3) yet exert opposing effects on the same gene targets.…”