Abstract

In order to investigate the presence of thermo-tolerant rock phosphate (RP) solubilizing anaerobic microbes during the fermentation process, we used grassland as sole organic substrate to evaluate the RP solubilization process under anaerobic thermophilic conditions. The result shows a significant decrease of pH from 6.5 to 4.8, and solubilizing from 7 to 15.8% of the phosphorus from the RP in the reactors after 90 days of incubation at 45°C. In these conditions, the organic acids produced were qualitatively and quantitatively identified as: acetic, butyric and propionic acids. This biological RP solubilization is due to the presence of a single thermo-tolerant bacterium isolated and identified as Bacillus subtilis from the anaerobic reactors. This B. subtilis strain was shown to be able to solubilize RP in liquid cultures containing insoluble RP as sole phosphate source. The mechanisms involved in these weathering processes confirmed the production of organic acids which were identified and quantified. This study is expected to lead to the development of novel, non-polluting farming practices by entering in the formulation of novel multi-functional biofertilizer by inoculating this thermo-tolerant phosphate-solubilizing bacterium into agricultural wastes as a practical and environmental strategy.

Key words: Grassland, phosphate, solubilization, Bacillus subtilis, thermo-anaerobic conditions.