Thermophilin ST9, a New Bacteriocin Produced by Streptococcus thermophilus CGMCC 1.1864

Abstract:

In this study, antimicrobial activity of the culture supernatant of Streptococcus thermophilus CGMCC 1.1864 was investigated with the agar diffusion method. The subsequent experiments results indicated the antimicrobial activity of the supernatant were not due to the existence of hydrogen peroxide and organic acid in the solution. The antimicrobial spectrum assays showed that the supernatant could inhibit the growth of both Gram-negative bacteria and Gram-positive bacteria. Heat stability test was also performed with the antimicrobial substance and no activity lost was observed after 2 h incubation at 100°C or 20 min at 121°C. However, its activity was reduced significantly if the boiling samples were transferred to ?20°C freezer for storage immediately. It was also tolerable to changes of pH levels, no significant reduction of its antimicrobial activity was observed at pH 2.0 through pH 9.0. The treatment of proteases and α-amylase could completely abolish the antimicrobial activity of the supernatant, while no activity loss was observed when treated with catalase. These results demonstrated that the antimicrobial substance belonged to bacteriocin family and was named as thermophilin ST9 tentatively. Since thermophilin ST9 could specially adsorb to the producing strain, pH-adsorption method was chosen to purify the bacteriocin, and subsequently the SephadexG-25 column chromatography was adopted to eliminate other proteins. Elution solution was further concentrated with freeze-drying method to obtain thermophilin ST9 powder. Purified thermophilin ST9 was subjected to Tricine-SDS- PAGE analysis and its molecular mass was determined to be 5.0 kD.

Key words:Streptococcus thermophilus, Bacteriocin, Purification, Antimicrobial activity, Antimicrobial spectrum