Useful Host-Vector Systems in Bacillus stearothermophilus.

We isolated a highly transformable thermophile, Bacillus stearothermophilus SIC1, which exhibited the following features. The growth temperature ranged from 45 to 65 degrees C in L broth. The maximum cell concentration in 2L broth (2% tryptone, 1% yeast extract, 0.5% NaCl, pH 7.2) was determined as an optical density at 660 nm of 7.8, and the generation time was 11 min at 60 degrees C. Strain SIC1 was a prototroph and was transformed by the protoplast procedure not only with repB plasmids (high-copy-number plasmids such as pTB913 and pUB110) but also with repA plasmids (low-copy-number plasmids such as pTB53). Transformation efficiencies with repB and repA plasmids were about 2 x 10 to 5 x 10 and 5 x 10 transformants per mug of DNA, respectively. The transformant carrying plasmid pTB913Y/K could grow at 63 degrees C in the presence of kanamycin. The regeneration frequency of protoplasts was 60%, and only 1 day was needed for regeneration at 55 degrees C.