Potassium transport loci in Escherichia coli K-12

Mutants of Escherichia coli K-12 requiring considerably elevated concentrations of potassium for growth are readily obtained as double mutants combining a kdp mutation with a mutation in one or more of five other loci. These loci are referred to as trk, for transport of K, because these mutations result in alterations in K transport. The kdp mutation is essential in the isolation and identification of this type of mutant; in a Kdp(+) strain, the presence of a trk mutation does not prevent growth of the strain in media containing very low concentrations of K. The trk loci are widely scattered over the E. coli chromosome; none of them is very near any other trk locus or near the kdp genes.