A mutation in the glta gene from a native isolate of the Pseudomonas chlororaphis subgroup induces a phenotypic change associated with phenazine production

Abstract

Members of the Pseudomonas genus colonise the rhizosphere of different plant species and display plant-probiotic traits. Among our collection of 19 isolates of native pseudomonads, isolate SPAN5 was obtained from a bulk soil sample of grasslands. This isolate, related with the Pseudomonas chlororaphis subgroup, showed several plant-growth promoting activities in vitro. We carried out Tn5 mutagenesis for identifying genes related to the biocontrol. We here report that the mutant clone SPAN5-135, which lost its orange pigmentation, suffered the insertion of Tn5 into the gltA gene encoding a type II citrate synthase (CS). The CS enzyme activity was reduced significantly in SPAN-135, as well as its phenazine production in several media. Also, siderophore and exoprotease secretion were affected. SPAN-135 could not recover the complete inhibition potential of the wild type version against the phytopathogenic fungi tested. This is the first report of the requirement of gltA for phenazine and siderophores production.