Identification, mapping and characterization of two genes of Escherichia coli K-12 regulating growth and resistance to streptomycin in cold

Escherichia coli MD1157, a routine isolate of AB1157 maintained in our labora tory, was noticed to have spontaneously acquired two conditional cold-dependent phenotypes: C-S (cold sensitivity) and Sm-SC (streptomycin sensitivity in cold). C-S involved delayed appearance of visible colonies on solid (LB or minimal) medium in cold (22 degrees C or below) without any loss of viability, and an extended lag period and longer doubling time following a temperature downshift in liquid medium. Sm-SC involved conditional suppression of the rpsL31-mediated streptomycin (Sm) resistance in cold, resulting in reduced colony forming ability in the presence of Sm. This phenotype was seen only on LB plates and weakly on minimal-medium plates containing some LB, but not on minimal medium alone. Genetic mapping traced these two phenotypes to mutations in two genes mapping to the 14-15 min region of the standard E. coli map, which have been named gicA (growth in cold) and gicB respectively. Comparison of MD1157 with transductants which had lost either one or both of these mutations showed that while gicB1 contributes only to Sm-SC, gicA1 is associated with both C-S and Sm-SC. Comparison of these strains with AB1157 suggested the involvement of a third, as yet unidentified gene in causing these phenotypes.