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The β-glucanase gene (bgl) from Bacillus amyloliquefaciens was expressed in E. coli CSH 55 under the control of the P R  promoter of phage λ that is repressed by the thermosensitive repressor C 1857 . Production of β-glucanase was drastically stimulated by a temperature shift to 42 C. This overexpression of the bgl gene (about 20% of the total cellular protein) led to an almost complete excretion of the otherwise periplasmic protein into the extracellular medium, β-glucanase accounted for more than 50% of the extracellular proteins. Col E 1 related plasmid (pEG 1) are amplified in E. coli relA strains in response to an amino acid limitation leading to a 10-fold increase in the activity of plasmid encoded genes. In this work we intended to maximize the expression of the bgl gene by a concerted action of a plasmid amplification and temperature induction. Surprisingly we could not increase the β-glucanase production above the level reached by plasmid amplification or temperature in­duction alone. The reasons for this unexpected result will be discussed. Under all conditions tested the expression of the bgl gene was much lower in the E. coli rel A strain NF 162 than in E. coli CSH 55; the low β-glucanase production was accompanied by a reduced excretion rate of the enzyme.

Excretion into the Culture Medium of a Bacillus ß-Glucanase after Overproduction in Escherichia coli