Fungal solubilization of rock phosphate is enhanced by forming fungal–rhizobial biofilms

Biosolubilization of rock phosphate (RP) using a Penicillium spp., an Aspergillus spp., Pleurotus ostreatus, Bradyrhizobium elkanii SEMIA 5019 and their fungal–rhizobial biofilms was investigated. Eppawala Rock Phosphate (ERP, total P concentration 17.6%), a RP from a deposit in Sri Lanka was used. Penicillium spp.–B elkanii SEMIA 5019 biofilm released the highest amount of P from the ERP with the highest P release-to-P uptake ratio. The P release of Penicillium spp. alone was significantly lower than that of its biofilm. Similarly, P. ostreatus–B. elkanii SEMIA 5019 biofilm showed a higher P release than P. ostreatus alone. However, P. ostreatus alone or its biofilm showed lower P release-to-P uptake ratios indicating relatively higher P uptake compared to the P release. The Aspergillus spp., showed a moderate P release. Large bradyrhizobial cell clusters attached to the mycelial mat of Penicillium spp. and P. ostreatus were observed under light microscope after 12 and 25 days of incubation, respectively. The present study, identified an effective method of fungal–rhizobial biofilm mediated solubilization of RP.