INVOLVEMENT OF PHENAZINES AND ANTHRANILATE IN THE ANTAGONISM OF PSEUDOMONAS-AERUGINOSA PNA1 AND TN5 DERIVATIVES TOWARD FUSARIUM SPP. AND PYTHIUM SPP

Pseudomonas aeruginosa PNA1, isolated from the rhizosphere of chickpea in India, suppressed Fusarium wilt of chickpea, caused by Fusarium ox ysporum f. sp, ciceris, and Pythium damping-off of bean, caused by Pyt hium splendens, When grown in culture, PNA1 produced the phenazine ant ibiotics phenazine-l-carboxylic acid and oxychloraphine, and inhibited mycelial growth of F. oxysporum f. sp. ciceris, P. splendens, and cer tain other phytopathogenic fungi. Two mutants (FM29 and FM13) deficien t in phenazine production were obtained following transposon mutagenes is of PNA1, The transposon in the genome of Fh429 was localized to phn A, which is thought to encode a subunit of anthranilate synthase II in volved in the phenazine biosynthesis. The FM13 mutation was complement ed by trpC, which encodes indole glycerol phosphate synthase in the tr yptophan biosynthesis pathway; consequently, FM13 could not grow on a minimal medium in the absence of tryptophan. Neither FM29 nor FM13 sup pressed Fusarium wilt of chickpea to the level achieved by the wild-ty pe strain, indicating that phenazine production contributed to the bio control of this disease by P. aeruginosa PNA1, FM29 was also less effe ctive than the phenazine-producing parental strain in biological contr ol of Pythium damping-off of bean, but FM13 was as effective as the pa rental strain in suppressing this disease. Anthranilate, an intermedia te in the tryptophan biosynthesis pathway, suppressed mycelial growth of Pythium spp, in culture and Pythium damping-off of bean and lettuce . Anthranilate, excreted by FM13 as a consequence of the trpC mutation , may have contributed to the suppression of Pythium damping-off by th e mutant.