Streptococcus pyogenes Malate Degradation Pathway Links pH Regulation and Virulence

Abstract

The ability of Streptococcus pyogenes to infect different niches within its human host most likely relies on its ability to utilize alternative carbon sources. In examining this question, we discovered that all sequenced S. pyogenes strains possess the genes for the malic enzyme (ME) pathway, which allows malate to be used as a supplemental carbon source for growth. ME is comprised of four genes in two adjacent operons, with the regulatory two-component MaeKR required for expression of genes encoding a malate permease (maeP) and malic enzyme (maeE). Analysis of transcription indicated that expression of maeP and maeE is induced by both malate and low pH, and induction in response to both cues is dependent on the MaeK sensor kinase. Furthermore, both maePE and maeKR are repressed by glucose, which occurs via a CcpA-independent mechanism. Additionally, malate utilization requires the PTS transporter EI enzyme (PtsI), as a PtsI -mutant fails to express the ME genes and is unable to utilize malate. Virulence of selected ME mutants was assessed in a murine model of soft tissue infection. MaeP -, MaeK -, and MaeR -mutants were attenuated for virulence, whereas a MaeE -mutant showed enhanced virulence compared to that of the wild type. Taken together, these data show that ME contributes to S. pyogenes' carbon source repertory, that malate utilization is a highly regulated process, and that a single regulator controls ME expression in response to diverse signals. Furthermore, malate uptake and utilization contribute to the adaptive pH response, and ME can influence the outcome of infection.A lthough it has a relatively small genome (approximately 1.8 Mbp), the pathogenic Gram-positive bacterium Streptococcus pyogenes has a remarkable ability to adapt to a variety of human tissues. This trait allows it to cause numerous diseases, ranging from superficial and self-limiting infections in soft tissues like the skin (impetigo) and pharynx (pharyngitis) to more problematic infections at a number of diverse anatomical sites (1). Understanding the complex regulatory interactions that allow it to adapt to these diverse environments provides a unique opportunity to gain insight into how a pathogen can efficiently employ a relatively limited genetic repertory to maximize its ability to cause disease.An important question is how S. pyogenes uses its limited metabolic potential to grow efficiently in diverse tissues. Considerable evidence has accrued to suggest that the patterns by which S. pyogenes exploits available growth substrates are intimately associated with both temporal and compartment-specific patterns of virulence gene expression (2-4). As a lactic acid bacterium, S. pyogenes relies exclusively on fermentation via the homolactic and mixedacid pathways to generate energy (5-7). However, the specific carbon sources it preferentially utilizes in different tissues, the temporal patterns with which these are consumed, and how these patterns impact regulation of virulence gene expression are not well understood.One approach to...

Discovery and Characterization of Human-Urine Utilization by Asymptomatic-Bacteriuria-Causing Streptococcus agalactiae

“…A recent study on group A streptococcus (51) identified malate degradation as a link between pH and virulence. Our findings of increased transcriptional activity of the maeE and maeP genes in ABSA in response to malate are also consistent with the response of group A streptococcus (51).…”

“…Therefore, we analyzed whether the growth of ABSA and UPSA strains would differ in a synthetic medium that contained a defined amount of malate. For this, we used SHU as defined in previous studies (56)(57)(58) supplemented with 40 mM malic acid, a concentration consistent with prior studies that have used 30 to 50 mM malic acid in vitro (51,(53)(54)(55)(59)(60)(61)(62). We observed that the growth of ABSA 834 and ABSA 729 was significantly higher than the growth of UPSA 058 and UPSA 714 in SHU (Fig.…”

“…The finding that ABSA can metabolize L-malic acid in urine is interesting; this compound is a widespread organic acid found at high levels in currants, rhubarb, green apples, and grape musts (61,78); pumpkin fruits (79); and wine (71) and is naturally excreted in human urine (70,71,80); its concentration varies dramatically depending on dietary intake. Other variable components in human urine include glucose (51,53,55,70) and fructose, which may inhibit metabolic pathways, including the ME pathway, as reported in Streptococcus lactis (81), E. faecalis (74), and L. casei (55). Considering the various levels of these components in human urine, we used a standardized SHU medium to compare the growth rates of WT and mutant ABSA under controlled growth conditions.…”

The malate sensing two-component system MaeKR is a non-canonical class of sensory complex for C4-dicarboxylates

“…The fact that maeK mutants in different species do not activate mae genes in response to the presence of L-malate 18, 22 clearly indicate that MaeK is a functional L-malate sensor. However, it is intriguing how a HK devoid of its ATP-dependent kinase activity can operate in signalling.…”

“…In S. pyogenes and L. casei , in addition to L-malate, low pH also induced the expression of maePE 22 . Interestingly, it has been shown that induction by low pH is independent of L-malate but requires a functional MaeK in S. pyogenes 22 .…”