The potential contribution of siderophore producing bacteria on growth and Fe ion concentration of sunflower (Helianthus annuus L.) under water stress

In the present study, 100 bacterial strains were isolated from the soil and tested for siderophore producing ability. Among siderophore producing bacteria, three superior isolates with the highest level of siderophore (F13, F58 and F66) selected for further study. Production of lecithinase, arginine dehydrolase, catalase, oxidase, hydrogen cyanide, indole acetic acid, solubilization of phosphate, gelatin hydrolysis, oxidative/fermentative, motility and gram staining by these strains was evaluated. In greenhouse experiment, the ability of selected isolates in solubilizing insoluble iron-containing compounds was examined at three moisture levels (0.45-0.6, 0.6-0.7 and 0.7-0.85 field capacity). Results showed that isolates F13 and F66 have greatest effects on chlorophyll amount and shoot dry weight compared to isolate F58. On average, iron concentration of sunflower in the presence of bacteria was 2.85-fold more than control, while it was 1.88-fold for roots. In addition, bacterial treatments enhanced resistance to water stress in sunflower. Based on biochemical tests and by comparison of 16S rRNA sequences, the F13, F58 and F66 isolates were closely related to Pseudomonas spp., Enterobacter spp. and Bacillus Sporothernodurans, respectively.