A strain of Pseudomonas putida that exhibited seedling disease control on cotton was among 5000 strains examined for unique properties that could be used to selectively recover genetically engineered pseudomonads from environmental samples. One isolate (M-17) was found to produce a red halo around single colonies grown on media containing 10 mg/l crystal violet. This decolorization reaction was constitutively produced when the growth medium contained glucose and asparagine, but was inhibited by the substitution of ammonia, nitrate or urea for the amino acid nitrogen source. However, a different medium containing succinic acid and using ammonia as the sole nitrogen source was found to induce the reaction. Factors that did not affect the decolorization reaction included temperature (14-30° C) and pH (3-8). Cultures of M-17 grown in broth containing crystal violet were able to decolorize still broth solutions, but not when incubated on a shaker (150 rpm). Stationary cultures formed a red precipitate. Efforts to characterize the precipitate revealed that it was soluble in polar organic solvents and insoluble in non-polar organic solvents. Thin layer chromatography revealed the presence of six bands that possibly represented various demethylated forms of crystal violet. Chemically derived mutants (cry-) did not produce a red halo but a clear, colorless region surrounding bacterial growth was observed. A greenhouse study demonstrated that strain M-17 provided protection against fungal disease as shown by plant stands on cotton (67% stand) equivalent to the commercial fungicides (70% stand) and significantly improved over the unamended control (38% stand). / Master of Science