L-serine degradation in Escherichia coli K-12: directly isolated ssd mutants and their intragenic revertants

Abstract

Two methods for the direct isolation of spontaneous ssd mutants of E. coli K-12 strains are described; by growth with L-serine as the C source, and by low-level kanamycin resistance. A newly isolated mutant had the same phenotype as the mutant described previously, including inefficient use glucose, inability to grow with succinate, altered transport characteristics and altered resistance to certain growth effectors. Succinate-utilizing derivatives, which appear to be intragenic, are characterized in detail. The relation between the mutants isolated here and mutants which are thought to have impairments in a system of coupling respiratory energy to active transport (ecfB mutants) is discussed.