Streptocyclin BTW is a novel member of a diverse family of circular bacteriocins in the genus <i>Streptococcus</i>

Members of the genus Streptococcus are gram-positive bacteria, commonly found in humans and animals. This group of microorganisms has been associated with severe infections and the development of resistance to antibiotics and production of bacteriocins. Many class I bacteriocins, especially lanthipeptides, have been described for streptococci; however, only one circular bacteriocin has been described for the group (uberolysin). The objective of this study was to characterize streptocyclin BTW, a 64 amino acid circular bacteriocin produced by Streptococcus devriesei DSM 19639, as well as to assess the diversity of circular bacteriocins within the genus. Streptocyclin BTW displayed a broad inhibitory spectrum with pronounced activity against strains of streptococci. A colony mass spectrum of the strain revealed a 6118.75 Da mass, which matches the predicted mass from sequencing. The gene cluster is composed of five genes: a core peptide (stpA), a membrane protein (stpB), a DUF95 family protein (stpC), an ATP-binding protein (stpD), and a putative immunity protein (stpE). Sequence Similarity Network (SSN) analysis revealed that streptocyclin BTW-like circular bacteriocins were found in Streptococcus orisasini, Streptococcus equi, Streptococcus pneumoniae, Streptococcus pseudopneumoniae, Streptococcus mitis, and Streptococcus bouchesdurhonensis species. This is the first report of a bacteriocin produced by S. devriesei.