Characterization of MtsR, a new metal regulator in group A streptococcus, involved in iron acquisition and virulence

Differential regulation of iron- and manganese-specific MtsABC and heme-specific HtsABC transporters by the metalloregulator MtsR of group A Streptococcus

The genome of the human pathogen group A Streptococcus (GAS) encodes the transporters MtsABC, FtsABCD, and HtsABC to take up ferric and manganese ions, ferric ferrichrome, and heme, respectively. The GAS genome also encodes two metalloregulators PerR and MtsR. To understand the regulation of the expression of these transporters, the mtsR and perR deletion mutants of a GAS serotype M1 strain were generated, and the effects of the deletions and Fe(3+), Mn(2+), and Zn(2+) on the expression of mtsA, htsA, and ftsB were examined. Mn(2+) dramatically depresses mtsA transcription and levels of the MtsA protein but does not downregulate the expression of htsA and ftsB. Fe(3+) decreases the expression of mtsA and htsA but has no effect on ftsB expression. Zn(2+) has no effect on the expression of all three genes. The deletion of mtsR abolishes the Mn(2+)- and Fe(3+)-induced depression of mtsA expression and the Fe(3+)-dependent decrease in htsA expression. The deletion of mtsR does not significantly alter GAS virulence in a mouse model of subcutaneous infection. The deletion of perR does not affect the expression of the genes in response to the metal ions. MtsR binds to the mts promoter region in the presence of Mn(2+) or Fe(2+). The results indicate that MtsR differentially regulates the expression of mtsABC and htsABC.

The SloR/Dlg metalloregulator modulates Streptococcus mutans virulence gene expression

Metal ion availability in the human oral cavity plays a putative role in Streptococcus mutans virulence gene expression and in appropriate formation of the plaque biofilm. In this report, we present evidence that supports such a role for the DtxR-like SloR metalloregulator (called Dlg in our previous publications) in this oral pathogen. Specifically, the results of gel mobility shift assays revealed the sloABC, sloR, comDE, ropA, sod, and spaP promoters as targets of SloR binding. We confirmed differential expression of these genes in a GMS584 SloR-deficient mutant versus the UA159 wild-type progenitor by real-time semiquantitative reverse transcriptase PCR experiments. The results of additional expression studies support a role for SloR in S. mutans control of glucosyltransferases, glucan binding proteins, and genes relevant to antibiotic resistance. Phenotypic analysis of GMS584 revealed that it forms aberrant biofilms on an abiotic surface, is compromised for genetic competence, and demonstrates heightened incorporation of iron and manganese as well as resistance to oxidative stress compared to the wild type. Taken together, these findings support a role for SloR in S. mutans adherence, biofilm formation, genetic competence, metal ion homeostasis, oxidative stress tolerance, and antibiotic gene regulation, all of which contribute to S. mutans-induced disease.

Molecular genetic anatomy of inter- and intraserotype variation in the human bacterial pathogen group A Streptococcus

In recent years we have studied the relationship between strain genotypes and patient phenotypes in group A Streptococcus (GAS), a model human bacterial pathogen that causes extensive morbidity and mortality worldwide. We have concentrated our efforts on serotype M3 organisms because these strains are common causes of pharyngeal and invasive infections, produce unusually severe invasive infections, and can exhibit epidemic behavior. Our studies have been hindered by the lack of genome-scale phylogenies of multiple GAS strains and whole-genome sequences of multiple serotype M3 strains recovered from individuals with defined clinical phenotypes. To remove some of these impediments, we sequenced to closure the genome of four additional GAS strains and conducted comparative genomic resequencing of 12 contemporary serotype M3 strains representing distinct genotypes and phenotypes. Serotype M3 strains are a single phylogenetic lineage. Strains from asymptomatic throat carriers were significantly less virulent for mice than sterile-site isolates and evolved to a less virulent phenotype by multiple genetic pathways. Strain persistence or extinction between epidemics was strongly associated with presence or absence, respectively, of the prophage encoding streptococcal pyrogenic exotoxin A. A serotype M3 clone significantly underrepresented among necrotizing fasciitis cases has a unique frameshift mutation that truncates MtsR, a transcriptional regulator controlling expression of genes encoding iron-acquisition proteins. Expression microarray analysis of this clone confirmed significant alteration in expression of genes encoding iron metabolism proteins. Our analysis provided unprecedented detail about the molecular anatomy of bacterial strain genotype-patient phenotype relationships.