Lehri, B., Seddon, A. and Karlyshev, A. (2014) Discovery and characterisation of a novel plasmid of a probiotic strain Lactobacillus fermentum 3872. In: International Conference on Antimicrobial Research; 01 - 03 Oct 2014, Madrid, Spain.

Abstract

Previous in vitro studies have demonstrated the outstanding probiotic properties of Lactobacillus fermentum strain 3872, which include enhanced antibacterial activities and the ability to adhere to various tissue culture cell lines (unpublished observations). The molecular basis for these properties and factors involved remained unknown until a draft genome sequencing of this bacterium became available (1). In particular, a partial sequence of a gene encoding an unusually large collagen-binding protein (CBP) has been reported (1). In this study we discovered and characterised plasmid pLF3872 carrying this and other genes that may be essential for the antibacterial properties of this microorganism. The complete sequence of the plasmid was derived in the course of a genome sequencing project using Ion Torrent PGM and 400nt sequencing kit. In addition to cbp, this circular 32 kb plasmid also contains thirty two other genes, including those encoding a toxin-antitoxin pair required for a stable maintenance of the plasmid within the strain. There is also a gene encoding a peptidoglycan hydrolase with a potential role in conjugation. The collagen binding protein encoded by the cbp gene was found to contain five repetitive ‘B domains’. These domains may be involved in the formation of a ‘stalk’ presenting a non-repetitive ‘A domain’ involved in adhesin. Interestingly, 3872 is the only strain of L. fermentum carrying the cbp gene. The CBPs produced by some other Lactobacillus spp contain only four B domains. Such adhesins are also produced by some pathogenic bacteria, e.g. Staphylococcus aureus which may explain the mechanism of a probiotic action based on competitive exclusion during attachment to host cells (2). The ability to produce a collagen binding protein may also allow the probiotic to compete against pathogenic bacteria bound to the same target protein resulting in colonisation of the site of infection followed by the release antimicrobial substances (such as bacteriocins and hydrogen peroxide).

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