IDENTIFICATION, MAPPING AND CHARACTERIZATION OF 2 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 condition al cold-dependent phenotypes: C-S (cold sensitivity) and Sm-SC (strept omycin sensitivity in cold). C-S involved delayed appearance of visibl e colonies on solid (LB or minimal) medium in cold (22 degrees C or be low) without any loss of viability, and an extended lag period and lon ger doubling time following a temperature downshift in liquid medium. Sm-SC involved conditional suppression of the rpsL31-mediated streptom ycin (Sm) resistance in cold, resulting in reduced colony forming abil ity in the presence of Sm. This phenotype was seen only on LB plates a nd weakly on minimal-medium plates containing some LB, but not on mini mal medium alone. Genetic mapping traced these two phenotypes to mutat ions in two genes mapping to the 14-15 min region of the standard E. c oli map, which have been named gicA (growth in cold) and gicB respecti vely. Comparison of MD1157 with transductants which had lost either on e 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 t hese strains with AB1157 suggested the involvement of a third, as yet unidentified gene in causing these phenotypes.