was employed by the method of Carlton and
Brown (2). A solution of Vogel-Bonner minimal medium (36)
containing 4% EMS was equilibrated at 37°C. To this solu-tion was added an equal volume of a late-exponential-phase
culture of P. aeruginosa PA103 grown in nutrient broth. This
mixture was incubated with shaking for 90 min at 37°C, and
then cells were washed with phosphate-buffered saline
(PBS), grown overnight in nutrient broth, and used to
inoculate skim milk plates at dilutions sufficient to result in
ca. 100 colonies per plate