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 Gram-negative 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 degreesC 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.