Bacillibactin-Mediated Improvement of Peanut Iron Nutrition, Yield, and Grain Quality by Bacillus cereus Rpea2 in Calcareous Soils

Abstract Iron deficiency in calcareous soils restricts peanut growth and yield. We isolated a high-siderophore strain, Bacillus cereus Rpea2, from the peanut rhizosphere intercropped with maize and assessed its effects on iron nutrition from mechanism to field performance. Genome analysis revealed a complete bacillibactin biosynthetic cluster. In hydroponics, Rpea2-derived siderophore alleviated iron-deficiency chlorosis, increased SPAD values, active iron in young leaves, and shoot biomass. Enhanced iron availability reduced expression of AhFRO1 and AhIRT1 and lowered root ferric-chelate reductase activity, indicating attenuation of the iron-deficiency response due to enhanced iron bioavailability. In calcareous field trials at two sites, Rpea2 inoculation significantly increased SPAD values, active leaf iron, yield, crude protein, crude fat, and kernel micronutrient concentrations. The agronomic effects were comparable to EDTA-Fe foliar application. These results demonstrate that Rpea2 enhances peanut iron nutrition through siderophore-associated mechanisms, highlighting its potential as a microbial biofertilizer for sustainable peanut production in calcareous soils.