On the fate of Bacillus cereus sensu lato in multi-species communities: biofilm formation and plasmid transfer
(2012) Biofilms 5 — Location: Paris (10.December.2012)
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- Bacillus cereus group is composed of highly related species which display distinct virulence spectra adapted to specific habitats. The emergence of various ecotypes and pathotypes has been driven by the exchange of mobile genes [1] [2] [3]. The group includes B. cereus sensu stricto and its close relative B. thuringiensis. They persist in numerous microcosms including soil, human tissues and food products [4] [5] [6]. They are able to colonize biotic and abiotic surfaces and form biofilms [7] [8]. These structured communities are often composed of multiple species that are kept in close contact and interact. This study aimed to gain more insight into the ecology of the B. cereus group and the potential transmission of genetic material towards other food-borne pathogens. The main objectives were, (i) to analyze the formation of B. thuringiensis biofilms in multi-species communities using controlled flow cell experiments, and (ii) to evaluate to what extent biofilm lifestyle impacts on the fate of a plasmid from B. cereus group. Intra- and inter-species conjugation efficiencies have been monitored in flow cell and static biofilms. The 72-kb plasmid pAW63 originated from B. thuringiensis sv. kurstaki [9] was chosen as model to estimate the plasmid transfer amongst B. thuringiensis strains and towards other Gram-positive species. A large set of flow cell experiments were performed to characterize and quantify mono-, bi- and tri-species biofilm formation involving both B. thuringiensis and Listeria ivanovii, in combination, or not, with the strong biofilm producer Staphylococcus epidermidis. After 72 h, biofilms formed by the sole B. thuringiensis consisted in large floccular structures composed of long chains strongly anchored to microcolonies attached to the glass surface. When inoculated with S. epidermidis, a synergistic effect was observed, with chains of Bacillus anchored to Staphylococcus clusters, themselves strongly attached to the surface. Reciprocally B. thuringiensis formed plait structures on which cells of S. epidermidis could grow. This research revealed that the biofilm lifestyle positively impacts on intra- and inter-species conjugation of pAW63. The frequencies of intra-species pAW63 transfer in a flow cell biofilm (4,4 x 10-1 Transconjugant/Recipient) were about 10 times higher than in liquid LB medium (5 x 10-2 T/R). Inter-species pAW63 transfer from B. thuringiensis to L. ivanovii reached a frequency about 500 times higher in both flow cell and static biofilms (10-4 T/R) than in liquid medium (5 x 10-7 T/R). References [1] Maughan H. and G. Van der Auwera (2011). Bacillus taxonomy in the genomic era finds phenotypes to be essential though often misleading. Infect Genet Evol, 11(5):789-797. [2] Rasko D. A., M. R. Altherr, C. S. Han, and J. Ravel (2005). Genomics of the Bacillus cereus group of organisms. FEMS Microbiol Rev, 29(2):303-329. [3] Tourasse N. J., E. Helgason, O. A. Økstad, I. K. Hegna, and A. Kolstø (2006). The Bacillus cereus group: novel aspects of population structure and genome dynamics. J Appl Microbiol, 101(3):579-593. [4] Vilain S., Y. Luo, M. B. Hildreth, and V. S. Brözel (2006). Analysis of the life cycle of the soil saprophyte Bacillus cereus in liquid soil extract and in soil. Appl Environ Microbiol, 72(7):4970-4977. [5] Bottone E. J. (2010). Bacillus cereus, a volatile human pathogen. Clin Microbiol Rev, 23(2):382-398. [6] Guinebretiere M. H., H. Girardin, C. Dargaignaratz, F. Carlin, and C. Nguyen-The (2003). Contamination flows of Bacillus cereus and spore-forming aerobic bacteria in a cooked, pasteurized and chilled zucchini purée processing line. Int J Food Microbiol, 82(3):223-232. [7] Kuroki R., K. Kawakami, L. Qin, C. Kaji, K. Watanabe, Y. Kimura, C. Ishiguro, S. Tanimura, Y. Tsuchiya, I. Hamaguchi, M. Sakakura, S. Sakabe, K. Tsuji, M. Inoue, and H. Watanabe (2009). Nosocomial bacteremia caused by biofilm-forming Bacillus cereus and Bacillus thuringiensis. Intern Med, 48(10):791-796. [8] Ryu J. and L. R. Beuchat (2005). Biofilm formation and sporulation by Bacillus cereus on a stainless steel surface and subsequent resistance of vegetative cells and spores to chlorine, chlorine dioxide, and a peroxyacetic acid-based sanitizer. J Food Prot, 68(12):2614-2622. [9] Van der Auwera G. A., L. Andrup, and J. Mahillon (2005). Conjugative plasmid pAW63 brings new insights into the genesis of the Bacillus anthracis virulence plasmid pXO2 and of the Bacillus thuringiensis plasmid pBT9727. BMC Genomics, 6:103.
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Citations
Henriet, O., Modrie, P., Vanzieleghem, T., & Mahillon, J. (2012). On the fate of Bacillus cereus sensu lato in multi-species communities: biofilm formation and plasmid transfer. Biofilms 5, Paris. https://hdl.handle.net/2078.5/40079