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Applied and Environmental Microbiology, February 2008, p. 1102-1110, Vol. 74, No. 4
0099-2240/08/$08.00+0     doi:10.1128/AEM.02030-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Inhibitory Spectrum of Thermophilin 9 from Streptococcus thermophilus LMD-9 Depends on the Production of Multiple Peptides and the Activity of BlpGSt, a Thiol-Disulfide Oxidase{triangledown} ,{dagger}

Laetitia Fontaine and Pascal Hols*

Unité de Génétique, Institut des Sciences de la Vie, Université catholique de Louvain, Place Croix du Sud 5, B-1348 Louvain-la-Neuve, Belgium

Received 5 September 2007/ Accepted 10 December 2007

The blpSt cluster of Streptococcus thermophilus LMD-9 was recently shown to contain all the genetic information required for the production of bacteriocins active against other S. thermophilus strains. In this study, we further investigated the antimicrobial activity of S. thermophilus LMD-9 by testing the susceptibility of 31 bacterial species (87 strains). We showed that LMD-9 displays an inhibitory spectrum targeted toward related gram-positive bacteria, including pathogens such as Listeria monocytogenes. Using deletion mutants, we investigated the contribution of the three putative bacteriocin-encoding operons blpDSt-orf2, blpUSt-orf3, and blpESt-blpFSt (bacSt operons) and of the blpGSt gene, which encodes a putative modification protein, to the inhibitory spectrum and immunity of strain LMD-9. Our results present evidence that the blpSt locus encodes a multipeptide bacteriocin system called thermophilin 9. Among the four class II bacteriocin-like peptides encoded within the bacSt operons, BlpDSt alone was sufficient to inhibit the growth of most thermophilin 9-sensitive species. The blpDSt gene forms an operon with its associated immunity gene(s), and this functional bacteriocin/immunity module could easily be transferred to Lactococcus lactis. The remaining three BacSt peptides, BlpUSt, BlpESt, and BlpFSt, confer poor antimicrobial activity but act as enhancers of the antagonistic activity of thermophilin 9 by an unknown mechanism. The blpGSt gene was also shown to be specifically required for the antilisteria activity of thermophilin 9, since its deletion abolished the sensitivities of most Listeria species. By complementation of the motility deficiency of Escherichia coli dsbA, we showed that blpGSt encodes a functional thiol-disulfide oxidase, suggesting an important role for disulfide bridges within thermophilin 9.

* Corresponding author. Mailing address: Unité de Génétique, Université catholique de Louvain, Place Croix du Sud 5, B-1348 Louvain-la-Neuve, Belgium. Phone: 32-10-478896. Fax: 32-10-473109. E-mail: hols{at}gene.ucl.ac.be

{triangledown} Published ahead of print on 21 December 2007.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, February 2008, p. 1102-1110, Vol. 74, No. 4
0099-2240/08/$08.00+0     doi:10.1128/AEM.02030-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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