P157: Effect of synthetic induction peptide on bacteriocin production in Streptococcus thermophilus

Bacteriocin synthesis in Streptococcus thermophilus is controlled by a complex blp operon. High levels of bacteriocin are produced only if the quorum-sensing regulatory mechanism is activated by the 30mer induction peptide (QSIP) of the blpC component.  We used synthetic QSIP to survey its impact on 40 strains of S. thermophilus that fail to produce bacteriocin in amounts detectable by agar diffusion assays. The addition of QSIP (250 ng/ml) to S. thermophilus cultures in the early or mid-log phase enhanced bacteriocin production in two additional strains that could be re-classified as bacteriocin producers. To confirm the regulatory effect of QSIP on bacteriocin production, we tested the effect of the 30mer peptide in a mutant of S. thermophilus in which the  blpC component was deleted and the culture was devoid of antimicrobial activity. Between concentrations of 25 and 250 ng/ml, the addition of QSIP to cultures growing at several stages of the growth curve resulted in the production of 3,200 units/ml of bacteriocin after 8 h of growth  at 37ºC. Addition of QSIP in late log phase (OD₆₆₀ = 1.0) when the medium pH is already 4.8 or lower, failed to induce bacteriocin production. 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 novel antimicrobial spectra by stimulating bacteriocin production in strains that display an apparently bacteriocin-negative phenotype.