The MicAB Two-Component Signaling System Is Involved in Virulence of Streptococcus pneumoniae

Abstract

In Streptococcus pneumoniae, the two-component signaling system MicAB was previously shown to contribute to repression of competence when oxygen is limited. In virulent strains expressing the serotype 2 and 6 capsule, mutation of the MicB kinase reduced the lag period of growth when cultures were switched from an aerobic to anaerobic atmosphere. After intranasal challenge of mice, the micB::km mutation decreased virulence, as shown by the absence of symptoms and by a lower level of recovery of CFU from lungs and blood. It is proposed that MicAB is involved in the adaptive response of the bacteria to changes in oxygen level during the course of infection.Streptococcus pneumoniae is an aerotolerant anaerobic human pathogen. During exponential growth in rich medium, central metabolism is essentially fermentative (4), despite NADH oxidase (1) and pyruvate oxidase (11), which reduce molecular substrate to H 2 O and H 2 O 2 , respectively. Implication of these oxidases in virulence (1, 11) indicates that oxidative metabolism is required for full virulence of S. pneumoniae. In vitro, oxidative metabolism also is involved in the control of genetic exchange via the regulation of competence for genetic transformation (1): competence is repressed under oxygen limitation (5).Integration of cellular redox status with competence occurs by phosphotransfer through the two-component systems (TCS) CiaRH and ComCDE (5-7). A third TCS, MicAB, contributes to repression of competence under oxygen limitation (7). Mutational analysis led to the proposal that the response regulator MicA is essential for bacterial growth, whereas the active form of the kinase, MicB, is not essential in vitro (7,9,12). MicB is the single protein in S. pneumoniae carrying the PAS signature (9).PAS domains are conserved motifs present in proteins that sense light or the redox and energetic status of the cell (2). Mutation of the PAS domain in MicB of S. pneumoniae abolishes the kinase activity of the recombinant protein and allows expression of competence under microaerobic conditions, suggesting that MicB phosphorylation both is dependent on PAS and constitutes one response to oxygen concentration (7).The requirement for this TCS in growth and in regulation of competence in vitro prompted us to investigate its role in the fate of pneumococci in vivo. The effect on in vivo growth and virulence of a mutation that annuls MicB kinase activity has been evaluated. Aerobic growth and anaerobic growth in vitro were studied for both serotype 2 and 6 pneumococcal micB::km mutants and their isogenic parents, and the virulence of these strains was determined with an in vivo model of pneumonia and bacteremia.The S. pneumoniae strains were a serotype 2 strain, D39 (NCTC 7466; National Collection of Type Cultures, London, United Kingdom), and a serotype 6B strain, S6 (10). Isogenic derivatives of these strains with the micB::km mutation were obtained by transformation of the wild-type strains with pPT12::Km, using 100 g of competence-stimulating peptide per ml (7). Trans...

Regulation of thepspAVirulence Factor and EssentialpcsBMurein Biosynthetic Genes by the Phosphorylated VicR (YycF) Response Regulator inStreptococcus pneumoniae

“…1) (21,59,60), and VicK contains a single transmembrane domain compared to the two transmembrane domains in other YycG homologues (43). Furthermore, pneumococcal vicK mutants are attenuated for virulence in murine models of infection (27,42), which further supports an important role for VicRK in pathogenesis.…”

“…In contrast to YycG homologues in other grampositive species (13,15,36), mutants containing the deletion for the gene encoding the pneumococcal VicK (YycG) HK grow in laboratory medium (see Fig. 1) (12,27,31,42,61,66). However, the VicK HK does become essential when the amount of the VicR RR is reduced from a regulatable promoter (42).…”

Evidence that the Essential Response Regulator YycF inStreptococcus pneumoniaeModulates Expression of Fatty Acid Biosynthesis Genes and Alters Membrane Composition

“…Mutation of the PAS domain in YycG abolishes its kinase activity and allows the expression of competence under microaerobic conditions. Also, Kadioglu et al (25) proposed that the YycFG TCS of the pneumococcus is involved in the adaptive response of the bacteria to changes in oxygen levels. Interestingly, changes in the fatty acid compositions of membrane lipid pools have been observed to occur in S. aureus cells transitioning between aerobic growth and anaerobic growth (43).…”

Defects in ex vivo and in vivo growth and sensitivity to osmotic stress of group A Streptococcus caused by interruption of response regulator gene vicR

“…Nevertheless, the essential processes regulated by VicRK in these organisms remain unknown. Defects in morphology and cell wall synthesis, decreased competence, sensitivity to antibiotics and fatty acids, attenuated virulence, and defects in biofilm formation have been associated with null vicK mutants or conditional mutants under non-functional conditions for VicR (Martin et al, 1999;Echenique & Trombe, 2001;Kadioglu et al, 2003;Ng et al, 2004;Senadheera et al, 2005). Some of these phenotypes appear to be organism-specific; however, no studies on GAS VicRK have been reported.…”