Identification and partial characterization of tochicin, a bacteriocin produced by Bacillus thuringiensis subsp tochigiensis

Bacillus thuringiensis subsp tochigiensis HD868 was identified as a bacteriocin producer which exhibited a bactericidal effect against closely related species, This bacteriocin designated as tochicin, was partially purified by 75% ammonium sulfate precipitation followed by subsequent dialysis, This partially purified tochicin showed a narrow antibacterial spectrum of activity against most of 20 typical B. thuringiensis strains and a strain of B. cereus, but not against other bacteria and yeasts tested, The antibacterial activity of tochicin on sensitive indicator cells disappeared completely by proteinase K treatment (1 mg ml(-1)), which indicates its proteinaceous nature, Tochicin was very stable throughout the range of pH 3.0-9.0 and was relatively heat-stable at 90 degrees C, but bacteriocin activity was not detected after boiling for 30 min, The relationship between cell growth and bacteriocin production was studied in a semi-defined medium, Tochicin activity was detected at the mid-log growth phase, reached the maximum at the early stationary phase, but decreased after the stationary phase, Direct detection of tochicin activity on sodium dodecyl sulfate-polyacrylamide gel suggested it has an apparent molecular mass of about 10.5 kDa, Tochicin exhibited a bactericidal activity against B. thuringiensis subsp thompsoni HD522 in phosphate buffer (pH 7.0).