SUMMARY: The synthesis of β-galactosidase by an constitutive mutant was examined in a chemostat using glucose-, glycerol-, succinate- or N-limited growth media. Except for glucose-grown bacteria, the steady-state intracellular level of β-galac-tosidase was maximal at dilution rates between 0.2 and 0.3 h. At higher dilution rates enzyme synthesis was reduced by catabolite repression, which could be relieved by the addition of cyclic AMP. With a catabolite-resistant mutant (UV5c), no decrease in enzyme level at high dilution rates was observed. All mutants examined were constitutive and gave decreased enzyme levels at low dilution rates, with the exception of /F′ UV5c mutants where the enzyme levels rose at low dilution rates. Hyper-producing mutants were isolated but were unstable. A constitutive mutant growing on glycerol-limited media was considered the most suitable for large-scale production of β-galactosidase in a chemostat.


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