title: RocA truncation underpins hyper-encapsulation, carriage longevity and transmissibility of serotype M18 group A streptococci.
abstract: Group A streptococcal isolates of serotype M18 are historically associated with epidemic waves of pharyngitis and the non-suppurative immune sequela rheumatic fever. The serotype is defined by a unique, highly encapsulated phenotype, yet the molecular basis for this unusual colony morphology is unknown. Here we identify a truncation in the regulatory protein RocA, unique to and conserved within our serotype M18 GAS collection, and demonstrate that it underlies the characteristic M18 capsule phenotype. Reciprocal allelic exchange mutagenesis of rocA between M18 GAS and M89 GAS demonstrated that truncation of RocA was both necessary and sufficient for hyper-encapsulation via up-regulation of both precursors required for hyaluronic acid synthesis. Although RocA was shown to positively enhance covR transcription, quantitative proteomics revealed RocA to be a metabolic regulator with activity beyond the CovR/S regulon. M18 GAS demonstrated a uniquely protuberant chain formation following culture on agar that was dependent on excess capsule and the RocA mutation. Correction of the M18 rocA mutation reduced GAS survival in human blood, and in vivo naso-pharyngeal carriage longevity in a murine model, with an associated drop in bacterial airborne transmission during infection. In summary, a naturally occurring truncation in a regulator explains the encapsulation phenotype, carriage longevity and transmissibility of M18 GAS, highlighting the close interrelation of metabolism, capsule and virulence.
authors.affiliation: Faculty of Medicine, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Nicola N
authors.initials: NN
authors.lastname: Lynskey
authors.affiliation: Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Goulding
authors.affiliation: Faculty of Medicine, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Gierula
authors.affiliation: Faculty of Medicine, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Claire E
authors.initials: CE
authors.lastname: Turner
authors.affiliation: Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom.
authors.forename: Gordon
authors.initials: G
authors.lastname: Dougan
authors.affiliation: Faculty of Medicine, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Edwards
authors.affiliation: Faculty of Medicine, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Shiranee
authors.initials: S
authors.lastname: Sriskandan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D018389:Codon, Nonsense; D005260:Female; D006801:Humans; D051379:Mice; D050296:Microbial Viability / Q000235:genetics*; D008969:Molecular Sequence Data; D009305:Nasopharynx / Q000382:microbiology; D012141:Respiratory Tract Infections / Q000382:microbiology / Q000635:transmission; D012703:Serotyping; D013171:Spores, Bacterial / Q000235:genetics; D013290:Streptococcal Infections / Q000235:genetics / Q000382:microbiology / Q000635:transmission; D013291:Streptococcus / Q000145:classification / Q000254:growth & development / Q000502:physiology*; D013297:Streptococcus pyogenes / Q000254:growth & development / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics*
chemical_list: D018389:Codon, Nonsense; C474644:RocA protein, Streptococcus pyogenes; D015534:Trans-Activators