Submitted to: Journal of Food Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2014
Publication Date: 2/1/2015
Citation: Somkuti, G.A., Renye Jr, J.A. 2015. Effect of a BlpC-based quorum-sensing induction peptide on bacteriocin production in Streptococcus thermophiles. Journal of Food Research. 4(1):88-96. DOI: 10.5539/jfr.v4n1p88.
Interpretive Summary: The production of many varieties of cheeses, yogurt and other dairy foods rely on the fermentation processes of specially selected and beneficial lactic acid bacteria. The primary product of these cultures is lactic acid that creates a mildly acidic environment to prevent or slow down the growth of undesirable microbes. In addition, selected types of lactic acid bacteria have the capacity to produce natural antimicrobial products called bacteriocins that inhibit the growth of unwanted spoilage and disease causing bacteria and extend the margin of safety and product shelf-life. In such cultures, bacteriocin synthesis is frequently dependent on the production of a special peptide, the quorum-sensing induction peptide (QSIP), whose presence triggers the series of reactions involved in bacteriocin production. ARS researchers used a synthetic form of the QSIP to prove that it is involved in turning on bacteriocin synthesis in the yogurt fermentation bacterium Streptococcus thermophilus. Further, the synthetic peptide was useful in finding lactic acid bacteria that appeared to be inactive due to the low level of QSIP present but responded well to the addition of synthetic QSIP and produced bacteriocins. The success of this approach demonstrated the possibility of discovering new types of bacteriocins in food grade lactic acid bacteria that have applications in protecting foods from disease causing bacteria.
Technical Abstract: 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.