Sequence analysis of pDN571, a plasmid encoding novel bacteriocin production in M-type 57 Streptococcus pyogenes

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Certain Streptococcus pyogenes strains produce a novel bacteriocin, streptococcin A-M57 (SA-M57).
• The production of SA-M57 is associated with specific M-protein types, particularly type 57.
• The genetic basis for SA-M57 production was previously unclear.

Purpose of the Study:

• To elucidate the genetic mechanisms underlying SA-M57 production in Streptococcus pyogenes.
• To characterize the plasmid responsible for SA-M57 synthesis.
• To determine the molecular details of the plasmid, including its replication origins and gene content.

Main Methods:

• Complete sequencing of the plasmid pDN571 from Streptococcus pyogenes 71-724.
• Identification of open reading frames (ORFs) and origins of replication (double-strand and single-strand).
• Bioinformatic analysis of genetic elements and comparison with known plasmid families.
• Analysis of the SA-M57 gene (scnM57) and its encoded protein product.

Main Results:

• The 3351bp plasmid pDN571 was fully sequenced, revealing three putative ORFs: repA, scnM57, and ORF3.
• Replication origins (double-strand and single-strand origin of type ssoA) were identified.
• Plasmid pDN571 belongs to the pC194/pUB110 family of rolling-circle plasmids.
• The SA-M57 bacteriocin is encoded by scnM57, synthesized as a 179-amino acid polypeptide with a 27-residue secretion signal peptide, and shows no homology to known proteins.

Conclusions:

• The plasmid pDN571 is directly responsible for the production of streptococcin A-M57 in Streptococcus pyogenes M-type 57 strains.
• The genetic and replication features of pDN571 align with the ubiquitous pC194/pUB110 rolling-circle plasmid family.
• The SA-M57 bacteriocin represents a novel class of antimicrobial peptides with a unique structure and function.