ORIGINAL ARTICLE A novel bacteriocin, thuricin 17, produced by plant growth promoting rhizobacteria strain Bacillus thuringiensis NEB17: isolation and classification E.J. Gray 1 , K.D. Lee 1 , A.M. Souleimanov 1 , M.R. Di Falco 2 , X. Zhou 1 , A. Ly 3 , T.C. Charles 3 , B.T. Driscoll 4 and D.L. Smith 1 1 Department of Plant Science, McGill University-Macdonald Campus, St Anne-de-Bellevue, QC, Canada 2 Genome Quebec/McGill University, Montreal, QC, Canada 3 Department of Biology, University of Waterloo, Waterloo, ON, Canada 4 Department of Natural Resource Sciences, Macdonald Campus of McGill University, St Anne de Bellevue, QC, Canada Introduction Bacteriocins are proteins produced by prokaryotes that are bactericidal and/or bacteristatic against organisms related to the producer strain (Jack et al. 1995). Depending on their structure, mode of action and chemical properties, four distinct classes are recognized (Klaenhammer 1993). For example, Nisin is a widely characterized bacteriocin produced from the lactic acid bacterium, Lactococcus lactis and has been accepted by World Health Organization as a food biopreservative (Delves-Broughton et al. 1996). Current applications of bacteriocins are as food preservatives while less research has been conducted on the agricultural applications of bacteriocins. Most known bacteriocin producing Bacillus strains are either from soil or food isolates. Bacillus thuringiensis HD2 synthesizes thuricin HD2, 950 kDa (Favret and Yousten 1989). Thuricin 7, 11Æ6 kDa, is produced by a soil isolate, B. thuringiensis BMG1Æ7 (Cherif et al. 2001). Keywords Bacillus, bacterial peptide, bacteriocin, plant growth promoting rhizobacteria, thuricin. Correspondence Don Smith, Department of Plant Science, McGill University-Macdonald Campus, 21 111 Lakeshore Road, St Anne-de-Bellevue, QC, Canada H9X 3V9. E-mail: dsmith@mcgill.ca 2004/1438: received 11 December 2004, revised and accepted 11 July 2005 doi:10.1111/j.1365-2672.2006.02822.x Abstract Aims: The aim of this study was to identify and characterize a compound pro- duced by the plant growth promoting bacterium, Bacillus thuringiensis non- Bradyrhizobium Endophytic Bacterium 17. Methods and Results: The bacterial peptide was analysed and purified via HPLC. Using the disk diffusion assay this peptide inhibited the growth of 16/ 19 B. thuringiensis strains, 4/4 Bacillus cereus strains, among others, as well as a Gram-negative strain Escherichia coli MM294 (pBS42). Both bactericidal and bacteristatic effects were observed on B. cereus ATCC 14579 and bactericidal effects were observed on B. thuringiensis ssp. thuringiensis Bt1267. The molecu- lar weight of the peptide was estimated via SDS-PAGE and confirmed with Matrix Assisted Laser Desorption Ionization Quadrapole Time of Flight mass spectrometry; its weight is 3162 Da. The peptide is biologically active after exposure to 100°C for 15 min, and within the pH range 1Æ00–9Æ25. Its activity disappeared when treated with proteinase K and protease, but not with a-amy- lase or catalase. Conclusions: We conclude that this is the first report of a bacteriocin produced by a plant growth promoting rhizobacteria (B. thuringiensis) species and have named the bacteriocin thuricin 17. Significance and Impact of the Study: Our work has characterized a bacteriocin produced by a plant growth promoting bacterium. This strain is previously reported to increase soya bean nodulation. Journal of Applied Microbiology ISSN 1364-5072 ª 2006 The Society for Applied Microbiology, Journal of Applied Microbiology 100 (2006) 545–554 545