Characterization of the RofA regulon in the pandemic M1global and emergent M1UK lineages of Streptococcus pyogenes

Abstract

Background & AimsThe standalone regulator RofA is a positive regulator of the pilus locus in Streptococcus pyogenes. Found in only certain emm genotypes, RofA has been reported to regulate other virulence factors, although its role in the globally dominant emm1 S. pyogenes is unclear. Given the recent emergence of a new emm1 (M1UK) toxigenic lineage that is distinguished by three non-synonymous SNPs in rofA, we characterized the rofA regulon in six emm1 strains, that are representative of the two contemporary major emm1 lineages (M1global and M1UK) using RNAseq analysis, and then determined the specific role of the M1UK-specific rofA SNPs. ResultsDeletion of rofA in three M1global strains led to altered expression of 14 genes, including six non-pilus locus genes. In M1UK strains, deletion of rofA led to altered expression of 16 genes, including 9 genes that were unique to M1UK. Only the pilus locus genes were common to the RofA regulons of both lineages, while transcriptomic changes varied between strains even within the same lineage. Although introduction of the 3 SNPs into rofA did not impact gene expression in an M1global strain, reversal of 3 SNPs in an M1UK strain led to an unexpected number of transcriptomic changes that in part recapitulated transcriptomic changes seen when deleting RofA in the same strain. Computational analysis predicted interactions with a key histidine residue in the PRD domain of RofA would differ between M1UK and M1global. SummaryRofA is a positive regulator of the pilus locus in all emm1 strains but effects on other genes are strain- and lineage-specific, with no clear, common DNA binding motif. The SNPs in rofA that characterize M1UK may impact regulation of RofA; whether they alter phosphorylation of the RofA PRD domain requires further investigation. Author summaryRofA belongs to the group of "mga-like" bacterial regulatory proteins that comprise a DNA binding domain as well as a phosphorylation domain (PRD) that is responsive to changes in sugar availability. In certain emm genotypes of Streptococcus pyogenes, rofA sits upstream of the pilus locus, to act as a positive regulator. The recent emergence of a SpeA exotoxin-producing sublineage of emm1 S. pyogenes, (M1UK) has focused attention on the role of RofA; M1UK and its associated sublineages are characterized by 3 non-synonymous SNPs in rofA, that include adjacent SNPs in the PRD domain. Here, we determine the impact of rofA deletion and the 3 rofA SNPs in both the widely disseminated M1global clone and the newly emergent M1UK clone. While production of SpeA undoubtedly contributes to infection pathogenesis, the evolution of M1UK points to a role for metabolic regulatory rewiring in success of this lineage.