TN5 INSERTION MUTANTS OF PSEUDOMONAS SP-267 DEFECTIVE IN SIDEROPHORE PRODUCTION AND THEIR EFFECT ON CLOVER (TRIFOLIUM-PRATENSE) NODULATED WITH RHIZOBIUM-LEGUMINOSARUM BV TRIFOLII

Pseudomonas sp. strain 267 isolated from soil promoted growth of diffe rent plants under field conditions and enhanced symbiotic nitrogen fix ation in clover under gnotobiotic conditions. This strain produced pyo verdine-like compound under low-iron conditions and secreted vitamins of the B group. The role of fluorescent siderophore production in the beneficial effect of strain 267 on nodulated clover plants was investi gated. Several non-fluorescent (Pvd(-)) Tn5 insertion mutants of Pseud omonas sp. strain 267 were isolated and characterized. The presence of Tn5 insertions was confirmed by Southern analysis of EcoRI digested g enomic DNA of each derivative strain. The siderophore-negative mutants were compared to the parental strain with respect to their growth pro motion of nodulated clover infected with Rhizobium leguminosarum by. t rifolii 24.1. We found that all isolated Pvd(-) mutants stimulated gro wth of nodulated clover plants in a similar manner to the parental str ain. No consistent differences were observed between strain 267 and Pv d(-) derivatives strains with respect to their plant growth promotion activity under gnotobiotic conditions.