Molecular basis of antifungal toxin production by fluorescent Pseudomonas sp strain EM 85 - A biological control agent

A fluorescent Pseudomonas sp. (strain EM 85) was found to inhibit growth of many soil-borne plant pathogenis fungi and effectively control fungal dise ases. The genetics governing this character was probed by mutagenesis follo wed complementation analysis after construction of a genomic library of the wild-type strain using the cosmid vector pLAFR 1. A cosmid clone, pANF 17 was able to complement the antifungal toxin production in a defective mutan t. The chromosomal origin of the DNA fragment in the cosmid clone was confi rmed by a Southern blot. Sub-clones of the three EcoRI fragments from pANF 17, however, failed in the complementation test. The complementing cosmid w as found to be stably maintained and expressed in the defective mutant unde r laboratory plate assay and in vivo conditions as evidenced by the extract ion and detection of the toxin and biological control experiment.