To identify the PhoP-regulated gene ( s ) responsible for motility on 0.3 % agarose low Mg2 + media , we tested the behavior of strains mutated in each of 19 different PhoP-activated genes ( mgtA , mgtB , mgtC , mig-14 , pagC , pagK , pagM , pagN , pagO , pagP , pcgL , pgtE , phoN , pmrD , rstA , slyA , ugtL , virK , and yobG ) .