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J Bacteriol, April 1998, p. 1988-1994, Vol. 180, No. 8
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Enterocins L50A and L50B, Two Novel Bacteriocins from Enterococcus faecium L50, Are Related to Staphylococcal Hemolysins

Luis M. Cintas,1,dagger Pilar Casaus,1,dagger Helge Holo,1 Pablo E. Hernandez,2 Ingolf F. Nes,1 and Leiv Sigve Håvarstein1,*

Laboratory of Microbial Gene Technology, Department of Biotechnological Sciences, Agricultural University of Norway, N-1432 Ås, Norway,1 and Departamento de Nutrición y Bromatología III, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040-Madrid, Spain2

Received 10 November 1997/Accepted 17 February 1998

Enterocin L50 (EntL50), initially referred to as pediocin L50 (L. M. Cintas, J. M. Rodríguez, M. F. Fernández, K. Sletten, I. F. Nes, P. E. Hernández, and H. Holo, Appl. Environ. Microbiol. 61:2643-2648, 1995), is a plasmid-encoded broad-spectrum bacteriocin produced by Enterococcus faecium L50. It has previously been purified from the culture supernatant and partly sequenced by Edman degradation. In the present work, the nucleotide sequence of the EntL50 locus was determined, and several putative open reading frames (ORFs) were identified. Unexpectedly, two ORFs were found to encode EntL50-like peptides. These peptides, termed enterocin L50A (EntL50A) and enterocin L50B (EntL50B), have 72% sequence identity and consist of 44 and 43 amino acids, respectively. Interestingly, a comparison of the deduced sequences of EntL50A and EntL50B with the corresponding sequences obtained by Edman degradation shows that these bacteriocins, in contrast to other peptide bacteriocins, are secreted without an N-terminal leader sequence or signal peptide. Expression in vivo and in vitro transcription/translation experiments demonstrated that entL50A and entL50B are the only genes required to obtain antimicrobial activity, strongly indicating that their bacteriocin products are not posttranslationally modified. Both bacteriocins possess antimicrobial activity on their own, with EntL50A being the most active. In addition, when the two bacteriocins were combined, a considerable synergism was observed, especially with some indicator strains. Even though the enterocins in some respects are similar to class II bacteriocins, several conserved features common to class II bacteriocins are absent from the EntL50 system. The enterocins have more in common with members of a small group of cytolytic peptides secreted by certain staphylococci. We therefore propose that the enterocins L50A and L50B and the staphylococcal cytolysins together constitute a new family of peptide toxins, unrelated to class II bacteriocins, which possess bactericidal and/or hemolytic activity.

* Corresponding author. Mailing address: Laboratory of Microbial Gene Technology, Department of Biotechnological Sciences, Agricultural University of Norway, N-1432 Ås, Norway. Phone: 47-64949464. Fax: 47-64947750. E-mail: sigve.havarstein{at}ibf.nlh.no.

dagger Present address: Departamento de Nutrición y Bromatología III, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040-Madrid, Spain.




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