Regulation of plasmid-encoded lactose genes in different gram-negative enterobacteriaceae

The expression and regulation of a variety of plasmid-encoded lactose systems have been studied in different gram-negative Enterobacteriaceae (Escherichia coli K-12, Serratia marcescens, and Enterobacter liquefaciens). They are similarly expressed in all strains, and they are inducible and sensitive to catabolite repression. Urea, known to bring about a specific catabolite repression effect, has been chosen to study some regulatory aspects of these plasmid-encoded lactose systems. We have shown that the expression of all lactose systems is inhibited by urea but the extent of the inhibition is strain dependent. This indicates that the genetic background of the host might modify in certain instances the expression of plasmid-encoded genes.