Phosphate chemical fertilizers are extensively used to improve agricultural productivity. However, the production of these fertilizers is expensive and can cause environmental damage. Alternatively, microbial solubilization of rock phosphate (RP) is a potential strategy for obtaining biofertilizers. This paper proposes the use of a novel combined mechanical-biological approach to produce soluble phosphate by cultivation of a selected strain of Aspergillus niger using RP With particle sizes in the nanometric range. The effect of Bayovar RP particle size on phosphate solubilization was analyzed for cultivations under submerged (SmF) and solid-state fermentation (SSF). The RP particle size played a key role in phosphate solubilization, with gains of up to 60% for SmF and 115% for SSF. The mechanical treatment of RP, combined with the biological cultivation process, resulted in an optimized solubilization of P, and it was shown that even short periods of milling could be highly effective. This proposed strategy could contribute to advances in the current bio-based economy and assist future developments in large-scale industrial production of biofertilizers. (C) 2017 Elsevier B.V. All rights reserved.