Evaluation of metal ions (Zn2+, Fe3+ and Mg2+) effect on the production of fusaricidin-type antifungal compounds by Paenibacillus polymyxa SQR-21

Effect of metal ions (Mg2+, Zn2+ and Fe3+) on the production of fusaricidin-type antifungal compounds by Paenibacillus polymyxa SQR-21 was studied in liquid culture. First, one-factor; three-level experiments were conducted to find out optimal concentrations of each metal ion for maximum production of fusaricidins. Later, three-factor; five-level experiments were performed and a quadratic predictive model was developed using response surface methodology (RSM). The results indicated that Fe3+ and Mg2+ positively affected the growth of P. polymyxa as determined by measuring the OD600 of the liquid culture. The production of fusaricidin-type antifungal compounds was significantly inhibited by Zn2+ (P = 0.0114) and increased by Mg2+ (P = 0.0051) but the effect of Fe3+ (P = 0.2157) was non-significant. However, a synergistic positive effect of Mg2+ and Fe3+ on the production of antifungal compounds was observed. This study sheds lights on the pertinent effects of the individual and combined metal ions on the production of fusaricidins in P. polymyxa. It provides the key information for optimization of the metal ions in the fermentation media to achieve the maximum antibiotic production in this strain.