Conversion of spent mushroom substrate to biofertilizer using a stress-tolerant phosphate-solubilizing Pichia farinose FL7

To develop high-efficient biofertilizer, an environmental stress-tolerant phosphate-solubilizing microorganism (PSM) was isolated from agricultural wastes compost, and then applied to spent mushroom substrate (SMS). The isolate FL7 was identified as Pichia farinose with resistance against multiple environmental stresses, including 5–45 °C temperature, 3–10 pH range, 0–23% (w/v) NaCl and 0–6 M ammonium ion. Under the optimized cultivation condition, 852.8 mg/l total organic acids can be produced and pH can be reduced to 3.8 after 60 h, meanwhile, the soluble phosphate content reached 816.16 mg/l. The P. farinose was used to convert SMS to a phosphate biofertilizer through a semi-solid fermentation (SSF) process. After fermentation of 10 days, cell density can be increased to 5.6 × 108 CFU/g in biomass and pH in this medium can be decreased to 4.0. SMS biofertilizer produced by P. farinose significantly improved the growth of soybean in pot experiments, demonstrating a tremendous potential in agricultural application.