Cloning of a phenazine biosynthetic locus of Pseudomonas aureofaciens PGS12 and analysis of its expression in vitro with the ice nucleation reporter gene.

Pseudomonas aureofaciens PGS12 produces three phenazine antibiotics, in addition to siderophores, hydrogen cyanide, pyrrolnitrin, and indoleacetic acid. Tn5-259.7 transposon mutagenesis was carried out to identify and clone a chromosomal locus involved in phenazine biosynthesis. Three classes of mutants were obtained: mutants deficient in phenazine production (Phz-), mutants deficient in hydrogen cyanide production (HCN-), and mutants deficient in the production of both compounds. EcoRI DNA fragments that contained the transposon and flanking regions were cloned from three mutants with single-transposon insertions, one from each phenotypic class. Phenazine and hydrogen cyanide production was restored by complementation of Phz- or HCN- mutants with selected cosmids from a PGS12 genomic library. No cosmids that complemented the doubly deficient Phz-HCN- mutant were obtained. A promoterless ice nucleation reporter gene was inserted in a phenazine biosynthetic locus by Tn3-spice transposon mutagenesis of a cosmid which complemented a phenazine-minus mutant. Reporter gene fusions that expressed the ice nucleation phenotype and no longer complemented phenazine production were introduced into the PGS12 chromosome by marker exchange. The expression of this locus was then monitored under different culture conditions. Expression decreased at pH levels below 7, and it was not affected by iron. Shikimic acid and phenylalanine favored higher expression levels. Expression was reduced in media with low substrate concentrations, indicating the importance of nutrient availability.