Stability of a lac operon in Zymomonas mobilis in batch and continuous culture

ZM6100(RP1::Tn951), a strain of Zymomonas mobilis containing the lactose transposon Tn 951 on the broad host range plasmid RP1, progressively lost all plasmid markers in batch culture under non-selective conditions. After 120 generations less than 0.1% of the population retained the plasmid markers. ZM6306, derived from ZM6100(RP1::Tn 951) by prolonged tetracycline selection, showed 100% stability for all plasmid markers when grown without selection pressure in both batch and continuous culture. In continuous culture, the synthesis of β-galactosidase was induced by the addition of lactose, and low levels of galactose were detected together with a small increase in ethanol concentration.