Effect of Temperature and Carbon Source on the Expression of $\beta$-Galactosidase Gene of Lactococcus lactis ssp. lactis ATCC 7962

The effects of growth temperature and a carbon source on the expression of β-galactosidase gene of Lactococcus lactis ssp. lactis ATCC 7962 (L. lactis 7962) were investigated. At 25°C, L. lactis 7962 had a higher β-galactosidase activity than cells grown at 30°C or 37°C, although cells grew most quickly at 37°C. The highest β-galactosidase activity was observed in cells grown in M17 with lactose (1%) followed by cells grown in a galactose (1%) medium. L. lactis 7962 exhibited the minimum β-galactosidase activity in glucose media, indicating catabolite repression. When the cellular levels of β-galactosidase mRNA were examined using slot blot hybridization, no significant differences were observed between cells grown at 25°C and cells at 30°C or 37°C in the same media. This suggests that the quantity of β-galactosidase mRNA may not be the reason for the higher β-galactosidase activities of L. lactis 7962 at 25°C. The level of ccpA (Catabolite Control Protein) transcript remained almost constant during the exponential growth phase irrespective of a carbon sourse.