To increase the nisin synthesizing activity of the natural strain Lactococcus lactis subsp. lactis 119 isolated from sour milk, UV irradiation in different doses was used followed by isolation of productive clones. The highest mutation effect was observed with the dose of 76,000 erg/mm2, when 11% of the cells increased their productivity by 12.8% at the minimum survival rate. Two-step UV irradiation and adaptive selection on the nisin-contaning medium provided isolation of a strain with the activity 42.6% higher than that of the initial strain (3850 IU/ml). Natural and UV-induced variability of the strain by the nisin synthesis, growth rate, carbohydrate consumption and sensitivity to antibiotics of various groups were studied.
Animals Lactococcus lactis