SUMMARY: Highest levels of β-galactosidase specific activity found after protracted growth of (syn. ) in lactose-limited chemostat culture were only developed with cultures previously conditioned to lactose in batch culture. The hyperactivities were not induced further by methyl thiogalactoside (MTG) and depended on dilution rate, being maximal at = 0.25 h. They were associated with increased substrate transport and utilization and, apart from a transient disturbance, were not affected by addition of glucose, galactose or glucose-6-phosphate to the lactose-limiting medium. Maltose addition produced a greater transient effect than the substances above, while citrate, α-methyl glucoside and 2-deoxy-glucose were inactive. Before hyperactivity developed, adding glucose led to a rapid decline and adding MTG led to a rapid increase in β-galactosidase activity. Methyl thiogalactoside exerted an inhibiting action at only the final stage, the bacterial yield being decreased, and its continued presence enabled glucose-adapted organisms to utilize glucose and lactose simultaneously. The lactose was utilized in two stages. α-Galactosidase hyperactivity occurred after protracted growth in melibiose-limited conditions, but β-glucosidase hyperactivity did not develop in cellobiose-limited medium.


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