Optimization of Rock Phosphate Solubilization in Submerged Cultures Containing Some Agro-Industrial Residues

Abstract

Aims: To solubilize rock phosphate in presence of agriculture wastes by microorganisms and produce fermented solution rich with soluble phosphate. Study Design: The effect of agriculture wastes, rock phosphate concentrations and culture conditions on rock phosphate solubilization. Identification of the potential isolate. Place and Duration of Study: Microbiology Dept., Fac. of Agriculture, Ain Shams Univ., Cairo, Egypt, 2015/ 2016. Methodology: Four isolates were tested on 7 agriculture wastes for rock phosphate solubilization. Optimization of some environmental factors. Identification of fungal isolate by 18S rRNA sequence analysis. Results: Some agro-industrial residues (bagasse, corn cobs, black sugar cane molasses, olive cake wastes, rice straw, sugar beet waste and whey) were used as a carbon source at different treatments for highest rock phosphate solubilization (RPS) by Serratia sp. Rs7 and Rs22, and Aspergillus sp. Bf6 and RPf10 isolates. The maximum RPS was obtained by the tested bacteria and fungi when both were grown on whey and sugar beet waste as a whole medium which increased the fermentation period to 10 and 12 days. All treatments of sugar beet wastes, bagasse, rice straw and corncobs failed to support RPS by bacterial isolates. Also corn cobs showed negative effect on RPS in all treatments for fungal isolates. In serial experiments, the maximum RPS was obtained by the tested bacteria and fungi in media supplemented with 7.0 and 10.0 gL-1 RP at pH 7.0 and 5.5 inoculated with 3% standard inoculum and incubated at 30°C respectively. The fermented solution produced by Aspergillus sp. RPf10 containing higher amounts of citric acid (543.39 μgP ml-1) and indole-3-acetic acid (11.96 mgL-1) as well as higher phosphatase activity than that produced by other tested isolates. This isolate was identified as Aspergillus tubingensis RPf10. Conclusion: the ability of Aspergillus tubingensis to convert sugar beet waste and insoluble rock phosphate into fermented solution containing maximum level of soluble phosphate, growth promoting and organic acids which can be apply this solution in future in microbial nutrient and agriculture field.