Lactococcus lactis subsp. lactis BGMN1-5 produces a leaderless class II bacteriocin called LsbB. To identify the receptor for LsbB, a cosmid library of the LsbB-sensitive strain BGMN1-596 was constructed. About 150 cosmid clones were individually isolated and transferred to LsbB-resistant mutants of BGMN1-596. Cosmid pAZILcos/MN2, carrying a 40-kb insert, was found to restore LsbB sensitivity in LsbB-resistant mutants. Further subcloning revealed that a 1.9-kb fragment, containing only one open reading frame, was sufficient to restore sensitivity. The fragment contains the gene yvjB coding for a Zn-dependent membrane-bound metallopeptidase, suggesting that this gene may serve as the receptor for LsbB. Further support for this notion derives from several independent experiments: (i) whole-genome sequencing confirmed that all LsbB-resistant mutants contain mutations in yvjB ; (ii) disruption of yvjB by direct gene knockout rendered sensitive strains BGMN1-596 and IL1403 resistant to LsbB; and (iii) most compellingly, heterologous expression of yvjB in naturally resistant strains of other species, such as Lactobacillus paracasei and Enterococcus faecalis , also rendered them sensitive to the bacteriocin. To our knowledge, this is the first time a membrane-bound peptidase gene has been shown to be involved in bacteriocin sensitivity in target cells. We also demonstrated a novel successful approach for identifying bacteriocin receptors.

Aim Assessment of biological control of P. syringae pv. aptata using crude lipopeptide extracts (CLEs) of two Bacillus amyloliquefaciens strains (SS‐12.6 and SS‐38.4) and one Bacillus pumilus strain (SS‐10.7). Methods and Results The minimum inhibitory concentration (MIC) of CLEs and their combinations against the pathogen and potential interaction between the extracts were determined in vitro. The most effective antibacterial activity was achieved with the CLE from B. amyloliquefaciens SS‐12.6, with an MIC value of 0.63 mg ml⁻¹. Interactions between CLE combinations were mostly indifferent. The biocontrol potential of CLEs, mixtures of CLEs, and cell culture of B. amyloliquefaciens SS‐12.6 was tested on sugar beet plants inoculated with P. syringae pv. aptata P53. The best result in inhibiting the appearance of tissue necrosis (up to 92%) was achieved with B. amyloliquefaciens SS‐12.6 cell culture. Conclusion This work demonstrated significant biocontrol potential of the CLE and cell culture of B. amyloliquefaciens SS‐12.6 which successfully suppress leaf spot disease severity on sugar beet plants. Significance and Impact of the Study The findings of biocontrol of sugar beet emerging pathogen will contribute to growers in terms of alternative disease control management. This study represent first assessment of biological control of P. syringae pv. aptata.