Poly(gamma-glutamic acid) (gamma-PGA) production by Bacillus subtilis NX-2 was carried out through solid-state fermentation with dry mushroom residues (DMR) and monosodium glutamate production residues (MGPR; a substitute of glutamate) for the first time. Dry shiitake mushroom residue (DSMR) was found to be the most suitable solid substrate among these DMRs; the optimal DSMR-to-MGPR ratio was optimized as 12:8. To increase gamma-PGA production, industrial waste glycerol was added as a carbon source supplement to the solid-state medium. As a result, gamma-PGA production increased by 34.8%. The batch fermentation obtained an outcome of 115.6 g kg(-1) gamma-PGA and 39.5 x 10(8) colony forming units g(-1) cells. Furthermore, a satisfactory yield of 107.7 g kg(-1) gamma-PGA was achieved by compost experiment on a scale of 50 kg in open air, indicating that economically large-scale gamma-PGA production was feasible. Therefore, this study provided a novel method to produce gamma-PGA from abundant and low-cost agroindustrial residues. (C) 2015 Elsevier Ltd. All rights reserved.