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Uberolysin: a novel cyclic bacteriocin produced by Streptococcus uberis

Ruth E. Wirawan^1,

¹ Department of Microbiology and Immunology, Otago School of Medical Sciences, University of Otago, PO Box 56, Dunedin, New Zealand
² Centre for Protein Research (Department of Biochemistry), Otago School of Medical Sciences, University of Otago, PO Box 56, Dunedin, New Zealand

Correspondence
John R. Tagg
john.tagg{at}otago.ac.nz

Streptococcus uberis is commonly found in the environment and in association with various bovine body sites and is a major cause of bovine mastitis. Moreover, S. uberis is known to produce a variety of bacteriocin-like inhibitory substances, antimicrobial agents that generally inhibit closely related bacterial species. In this respect, S. uberis strain 42 has previously been shown to produce a novel nisin variant named nisin U. This paper reports that, in addition to nisin U, S. uberis strain 42 produces a second bacteriocin that induces the lysis of metabolically active, susceptible target bacteria and which has therefore been named uberolysin. Isolation of the native active antimicrobial agent revealed that uberolysin is a 7048 Da peptide that is refractory to sequence analysis by Edman degradation. Transposon mutagenesis was used to generate a uberolysin-negative mutant of S. uberis 42 and sequencing of DNA flanking the insertion site revealed, in addition to the structural gene (ublA), several open reading frames likely to be involved in post-translational modification, transport and producer self-protection (immunity), and possibly in regulation of the biosynthetic gene cluster. In addition, a pair of direct repeats that may be involved in bacteriocin acquisition were identified; indeed, ublA could be identified in 18 % of tested S. uberis strains. Enzymic hydrolysis of uberolysin was used to confirm that ublA does indeed encode the precursor of uberolysin, that an unusually short leader sequence of only six amino acids is cleaved during processing of the mature peptide and that uberolysin is post-translationally covalently modified to form a head-to-tail monocycle. Thus, uberolysin is a unique cyclic bacteriocin, belonging to the same family of bacteriocins as enterocin AS-48 and circularin A.

The GenBank/EMBL/DDBJ accession number of the sequence reported in this paper is DQ650653.

Present address: Department of Food Science, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, NJ 08901, USA.

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