Copyright ©) 1994, American Society for Microbiology Expansion of Bacteriocin Activity and Host Range upon Complementation of Two Peptides Encoded

Lactacin F is a membrane-active bacteriocin produced by Lactobacillus johnsonii VP111088 (Laf). The genetic determinants encoding lactacin F are organized in a 1-kb polycistronic operon composed of a promoter (Plaf), three genes (lafA, laJX, and ORFZ), and a functional rho-independent transcription terminator. Two Laf- derivatives of VP111088, designated NCK64 and NCK65, were characterized. NCK64 contained a frameshift mutation in the lafA gene causing premature termination of translation. NCK65 harbored a 10-kb chromosomal deletion covering the laf operon. When the lafA gene was cloned independently and expressed in NCK65, bacteriocin activity was limited to L. helveticus 87, only one of the six known lactacin F-sensitive (Lar) indicators. When laJX was introduced into NCK65, no bacteriocin activity against any of the sensitive strains was detected. Genetic combination of lafA and laIX, in cis or in trans, restored bacteriocin activity against all Lar indicators. When two NCK65 clones containing either lafA or laJXwere plated slightly apart on agar plates, fully active lactacin F was present in the intervening area where the two excreted gene products, LafA and LafX, diffused together. The genetic analysis revealed that the interaction of two bacteriocinogenic peptides encoded within the laf operon is likely to participate in the formation of poration complexes in the membranes of susceptible bacteria. Bacteriocins are biologically active peptides, proteins, o