Effect of Salt Concentration on Siderophore Production by Rhizobium strains nodulating Macrotyloma uniflorum (Lam.) verdc

Thirty two Rhizobium strains isolated from ischolar_main nodules of Macrotyloma uniflorum (Lam.) Verdc. showed siderophore production on Chrome-Azurol S agar medium. Ten Rhizobium strains which showed varying siderophore production at control (without salt) were selected to study the effect of salt concentration on siderophore production. These strains showed low siderophore production at control and it increased with increasing salt concentration up to 1000mM by the strain HGR23 (80μg/mL^-1) while two strains HGR16 and HGR30 showed at 400mM concentration. Salt stress enhanced maximum siderophore production (90 μg/mL^-1) by the strains HGR5 and HGR8 at 600mM salt concentration over control. Later, the siderophore production decreased with increasing salt concentration. The strains HGR1, HGR4, HGR7, HGR12 and HGR18 showed maximum production at 800mM salt concentration (60.7 μg/mL^-1 to 70.8 μgmL^-1). Paper Electrophoresis of the siderophore extract showed the presence of trihydroxamate type of siderophores.