Siderophore Production by Rhizosphere biological control bacteria Brevibacillus brevis GZDF3 of Pinellia ternata and its antifungal effects on Candida albicans.

B. brevis GZDF3, a gram-positive bacterium, was a plant growth-promoting rhizosphere bacterium (PGPR) isolated from the rhizosphere soil of Pinellia ternate (an important Chinese Traditional Medicinal herb). The GZDF3 strain produced certain active compounds, such as siderophore, which were the final metabolite products of non-ribosomal peptide synthetase (NRPS) and independent non-ribosomal peptide synthetase (NIS) activity. The present study attempted to investigate the siderophore production characteristics and conditions by Bacillus sp. GZDF3. And the antibacterial activity of siderophore on pathogenic fungi was also investigated. The optimal conditions for the synthesis of siderophore were determined by single factor method, sucrose 15 g/L, asparagine 2 g/L, 32 °C and, 48 h. The optimized SA（Sucrose-Asparagine Medium）medium significantly increased the production of siderophore, from 27.09% to 54.99%. Effects of different kinds of metal ions on siderophore production were explored here. It showed that Fe³⁺ and Cu²⁺ significantly inhibited the synthesis of siderophore. The preliminary separation and purification of siderophore by immobilized metal affinity chromatography (IMAC) has strong antibacterial activity against Candida albicans. The synergistic effect of siderophore and Amphotericin B was demonstrated. Our results have shown that the GZDF3 strain could produce a large amount of siderophore and has strong antagonistic activity, which is helpful in the development of new biological control agents.