Effect of Different Metals on Synthesis of Siderophores by Endophyte Bacteria Isolated from Various Annual Plants

Endophyte bacteria are microorganisms that pass all or part of their life cycle in the tissues of healthy plants without causing any obvious signs of disease. Most siderophore-producing endophytic bacteria could improve the plant growth. Here, the effect of metals, iron (Fe), nickel (Ni), and cobalt (Co), on the growth and siderophore production profiles of 30 endophyte bacterial isolates were investigated. The results of the Minimum Inhibition Concentration (MIC) tests showed that endophytes exhibit varying degrees of tolerance to heavy metals and the metal tolerance decreased in the order Fe3+>Ni2+>Co2+. It was revealed that while 10 isolates could not produce siderophores under any circumstances, 20 isolates produced siderophores at different degrees, and siderophore molecules synthesized and secreted by these 20 isolates had affinities for all three metals (Fe3+, Co2+, and Ni2+). In addition, siderophore production profiles of isolates under each heavy metal stress were investigated by adding these metals to the Chromium Azurol Sulfonate (CAS) medium at optimum concentration. The results suggested that siderophore synthesis could be one of the coping mechanisms of only two isolates with Co2+ and Ni2+ heavy metals. In the final stage of the study, molecular identification of a certain number of isolates selected according to their siderophore production values was carried out by 16S rRNA sequencing. As a result of the sequence analysis, 2 Pseudomonas sp., 4 Bacillus sp., 1 Chryseobacterium sp., 1 Staphylococcus sp., and 1 Peribacillus sp. were revealed.