FIG. 6.

Growth and β-galactosidase activity of L. lactis NCDO2054 in M17 medium containing galactose (A) or lactose (B). A 16-h culture of strain NCDO2054 grown in M17-glucose was pelleted, washed, and resuspended (1:10) in fresh M17 broth supplemented with 0.5% galactose or lactose. At hourly time intervals, the OD₆₀₀ (—♦—) was measured and a 10-ml sample was removed to assay for β-galactosidase activity. One unit of β-galactosidase enzyme is equivalent to 1 μmol of o-nitrophenol released from o-nitrophenyl-β-d-galactopyranoside (ONPG) per minute. The β-galactosidase activity, in units per milligram of total protein, is indicated (---•---).