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Effect of a BlpC-based quorum-sensing induction peptide on bacteriocin production in Streptococcus thermophilus

Somkuti, George A., Renye, J. A., Jr.
Journal of food research 2015 v.4 no.1 pp. 88-96
Streptococcus thermophilus, antibacterial properties, bacteriocins, developmental stages, loci, mutants, pH, peptides, phenotype, quorum sensing
Bacteriocin synthesis in Streptococcus thermophilus is controlled by a complex blp locus. High levels of bacteriocin are produced only if the quorum-sensing regulatory mechanism is activated by the 30mer induction peptide (QSIP) which is embedded in the BlpC protein product of the blpC component. To confirm the regulatory effect of QSIP on bacteriocin production, we tested the effect of the 30mer peptide in a mutant of S. thermophilus NRRL-B59671 in which the blpC component was deleted and the culture was devoid of antimicrobial activity. Between concentrations of 30 and 250 ng/ml, the addition of QSIP to cultures growing at several stages of the growth curve resulted in the production of up to 3,200 units/ml of bacteriocin after 8 h of growth at 37ºC. Addition of QSIP to the culture in late log phase (OD660 ≥ 1.0) when the medium pH is already 4.8 or lower, failed to trigger bacteriocin production. We used synthetic QSIP to survey its impact on 35 strains of S. thermophilus that fail to display bacteriocin activity by agar diffusion assays. The addition of QSIP (250 ng/ml) to S. thermophilus cultures in the early or mid-log phase induced bacteriocin production in two additional strains that could be re-classified as bacteriocin producers. The results confirmed the involvement of a quorum-sensing regulatory mechanism in bacteriocin synthesis in S. thermophilus and also demonstrated the utility of the 30mer QSIP in discovering bacteriocins with potentially novel antimicrobial spectra by enhancing bacteriocin production in strains with an apparently bacteriocin-negative phenotype.