Effects of nutrients on α‐amyiase production and plasmid stability in fed‐batch culture of recombinant bacteria

Escherichia coli harbouring a recombinant plasmid containing the α‐amylase gene (HB101/pHI301) and its derivative which can stably maintain the plasmid (HB101/pHI301A) were cultivated in a mini‐jar fermenter. By controlling dissolved oxygen (DO) at a concentration of 2–3 μg/l and supplementing with suitable amounts of nutrients, the organisms could grow to a concentration (up to 40 g dry cell l−1) in a semi‐synthetic casamino acid medium. During culture the plasmid was maintained stably in both strains. In a synthetic medium, both micro‐organisms grew less well and plasmid‐free segregants were observed with HB101/pHI301 during the fed‐batch culture. On the other hand, plasmid pHI301A was stably maintained throughout the fed‐batch culture of HB101/pHI301A. Growth inhibitors, which may be metabolic products, accumulated in the medium and reduced bacterial growth.