Purification and characterization of thermophilin ST-1, a novel bacteriocin produced by Streptococcus thermophilus ACA-DC 0001

Thermophilin ST-1 is produced by Streptococcus thermophilus ACA-DC 0001, a "wild" strain isolated from traditional Greek yogurt products.It exerts an inhibitory effect on lactic acid bacteria, several food spoilage and food-borne pathogenic microorganisms, and some Gramnegative phytopathogen bacteria, including Listeria innocua BL 86/20 , Enterococcus faecalis EF1, Staphylococcus aureus ATCC 29996, Xanthomonas campestris BPIC 1660, Pseudomonas syringae BPIC 1549 and Erwinia rubrifasciens BPIC 1710.The crude antimicrobial compound is heat-labile (60 °C for 10 min) and sensitive to the proteolytic enzymes pronase and trypsin and high acidic and alkaline conditions, and shows a bactericidal mode of action against the indicator strain Lactococcus lactis ssp.cremoris CNRZ-117.Production of thermophilin ST-1 starts during the early growth of the producer strain and reaches a maximum titer of 2560 AU•mL -1 at the end of the exponential growth.Thermophilin ST-1 was partially purified by ammonium sulfate precipitation, ionexchange and size-exclusion chromatography.SDS-PAGE electrophoresis of purified thermophilin ST-1 showed a single protein band with a molecular mass of 30 kg•mol -1 , classifying this novel bacteriocin with the large heat-labile proteins.Until now, however, the molecular mass of bacteriocins reported in the species of S. thermophilus was less than 10 kg•mol -1 (small, heat-stable peptides).Curing experiments did not result in the loss of bacteriocin production, suggesting that the genetic determinant is probably located on the chromosome. Streptococcus thermophilus / bacteriocin / thermophilin / lactic acid bacteria / antimicrobial activity / phytopathogenRésumé -Purification et caractérisation de la thermophiline ST-1, une nouvelle bactériocine produite par Streptococcus thermophilus ACA-DC 0001.La thermophiline ST-1 est une bactériocine produite par Streptococcus thermophilus ACA-DC 0001, une souche «sauvage» isolée d'un yaourt traditionnel Grec.Elle présente un large spectre d'activité contre les germes pathogènes alimentaires ainsi que contre certaines bactéries Gram-négatives phytopathogènes.Elle inhibe, non seulement, des bactéries lactiques mais également, les souches Listeria innocua BL 86/20, Enterococcus faecalis EF1, Staphylococcus aureus ATTC 29996, Xanthomonas campestris BPIC 1660, Pseudomonas syringae BPIC 1549 et Erwinia rubrifasciens BPIC 1710, ainsi que la souche indicatrice Lactococcus lactis ssp.cremoris CNRZ-117.L'extrait brut antimicrobien est sensible aux enzymes protéolytiques pronase et trypsine, à la température de 60 °C après 10 min et aux conditions très acides et très alcalines.