Effect of a BlpC-Based Quorum-Sensing Induction Peptide on Bacteriocin Production in Streptococcus thermophilus

Abstract

Bacteriocin synthesis in some Streptococcus thermophilus strains is under the control of a complex blp locus but bacteriocin is produced only when a quorum-sensing regulatory mechanism is activated by the protein product of the blpC component. To demonstrate the regulatory effect of BlpC in S. thermophilus ST110 (NRRL-B59671), which naturally produces bacteriocin, the effect of the 30mer quorum-sensing induction peptide (QSIP) embedded in BlpC was tested in a knockout mutant in which the blpC gene was eliminated and was devoid of antimicrobial activity. Between concentrations of 30 and 250 ng/ml, the addition of synthetic QSIP to cultures at several points of the growth curve resulted in the accumulation of up to 3,200 units/ml of bacteriocin after 8 h of growth at 37 ºC. Addition of QSIP to the culture in late log phase (OD 660 ≥ 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 do not 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 strains that could be re-classified as bacteriocin producers. The results demonstrated the involvement of a quorum-sensing regulatory mechanism in bacteriocin synthesis in S. thermophilus ST110 and also demonstrated the utility of the 30 mer QSIP in discovering bacteriocins with potentially novel antimicrobial spectra by enhancing bacteriocin production in other strains of S. thermophilus that ordinarily display a bacteriocin-negative phenotype.

The Genomic Basis of the Streptococcus Thermophilus Health-Promoting Properties

“…Softwares were also developed to predict in silico bacteriocin loci from genomes, such as antiSMASH (114)(115)(116) and BAGEL4 (117)(118)(119). If more than 20 strains of STH have been reported in the literature as bacteriocin producers, only ve genomes of those strains were sequenced in August 2021 : B59671 (120), LMD-9 (121,122), KLDS 3.1003 (123), ST106 and ST109 (124).…”

Complete Genome Sequences of Bacteriocin-Producing Streptococcus thermophilus Strains ST106 and ST109

“…The blp gene cluster has been characterized for S. thermophilus strains LMD-9 (3), ST106, and ST118 (4), where bacteriocin production was induced with a recombinant or synthetic quorum sensing peptide, BlpC-30, and for strain B59671 (5, 6), where production occurs naturally.…”

“…thermophilus strains ST106 and ST109, raw milk isolates from our in-house culture collection. The strains have previously been reported to produce the broad-spectrum bacteriocins thermophilin 106 and thermophilin 109, respectively (4, 7). S.…”

“…thermophilus strains (6, 13), the ST109 genome contained 13.5% nonfunctional genes; however, ST106 possessed 323 pseudogenes, corresponding to 16.8% of the predicted coding sequences. Previous studies showed that thermophilin 109 was naturally produced and may be encoded within the blp gene cluster (4, 7). The Clone Manager software version 9 (Sci-Ed Software, NC) was used to compare the chromosomal locus flanked by blpA and blpX, which consisted of 13,350 nt in ST106 and 13,332 nt in ST109.…”

Complete Genome Sequence of Streptococcus thermophilus Strain B59671, Which Naturally Produces the Broad-Spectrum Bacteriocin Thermophilin 110

“…Some S. thermophilus strains have been investigated for their production of broad-spectrum antimicrobial peptides called bacteriocins. Several strains naturally produce bacteriocins ( 1 – 7 ), while others require a synthetic 30-mer quorum-sensing peptide, BlpC30, to induce production ( 8 – 10 ). The chromosomal locus encoding BlpC30-induced bacteriocins was designated the bacteriocin-like peptide ( blp ) gene cluster when characterized in strains LMD-9, LMG18311, and CNRZ1066 ( 11 ).…”